JPRS ID: 10126 TRANSLATION ANTIRADAR CAMOUFLAGE BY YU. G. STEPANOV

• Document Type: CREST
• Collection: JPRS
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00850R000400070041-5
• Release Decision: RIF
• Original Classification: U
• Document Page Count: 119
• Document Creation Date: November 1, 2016
• Sequence Number: 41
• Content Type: REPORTS

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY .
JPRS L/ 10126
19 November 1981
Translati~n
ANTIRADAR CAMOUFLAGE
~ BY
Yu. G. Stepanov
Fg~$ FOR~`CN BROADCAST INFORMATION SERVICE
~
FOR OFF[CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
NOTE
- JPRS publications contain information primarily from foreign
newspapers, periodicals and books, but also from news agency
transmissions and broadcasts. Materials from foreign-language
saurces are translated; those from English-language sources
are transcribed or reprinted, with the original phrasing and
other characteristics retained.
Headlines, editorial reports, and material enclosed in brackets
are supplied by JPRS. Processing indicators such as [Text]
_ or [Excerpt] in the first line of each item, or following the
last line or a brief, indicate how the original inforcration was
processed. Where no processing indicatc~r is given, the infor-
mation was summarized or extrac"ted.
Unfamiliar names rendered phoneticslly or transliterated are
enclosed in parentheses. Words or names preceded by a ques-
tion mark and enclased in parentheses were not clear in the
original bu* have been siipplied as appropriate in context.
Other unattributed parenthetical notes within the body of an
item originate witn the source. Times within items are as
- given by source.
~
The contents of this publication in no way represent the poli-
cies, views or attitudes of the U.S. Government.
COPY�.IGHT LAWS Ai1D REGULATIONS GOVERNING OW~IERSHiP OF
MEITERIALS REPRODUCED HEREIN REQUIRE THAT DISSEMINATION
OF THIS PUBLICATiON BE RESTRICT~:D FOR OFFICIAL USE 0?~TL,Y.
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/42/09: CIA-RDP82-40850R000400470041-5
FOR OFFICIAL USE ONLY
~ JPRS L/10126
19 November 1�81
_ ANTIRADAR CAMOUFLAGE
Moscow PROTIVORADIOLOKATSIGNNAYA MASKIROVKA in Russian 1968 (signed to
press 26 Apr 68) pp 2-144
[Book by Yuriy Grigor'vevich Stepanov, Izdatel'stvo "Sovetskoye Radio",
Moscow, 12,200 copies, 144 pages, UDC 623.68]
' CONTENTS
Annotation 1
Introduction 2
' Chapter 1. The Reflective Properties of Radar Targets 4
I 1. Tiie effective back-scatter cross-section 4
~ 2. Amplitude fl~:ctuations of returns and the radar cross-sections of
targets 8
3. Phase front f luctuations of a retuxn 15
- 4. The polarization characteristics of a return 17
S. The effective target cross-section in the case of diversity
(bistatic) radars 18
i
~
6. The average values of the effective radar scatter cross-section of
real targets 22
i ~hapter 2. Experimental Studies of Effective Target Back-Scatter
I Cross-Sections 23
l. Methods of experimentally studying the effective radar cross- '
section 23
2, Specif ic features of electromagnetic simulation 24
3. Measuremen~ systems for the study of effective radar cross-sections
with models 2~
4. The RAT SCAT faci~.ity for the measurement of the effective radar
- cross-se~tions of various objects 3z
- - a - [II - USSR - FOUO]
- [III - USSR - 4 FOUO]
FOR OFFICIP.L USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
EOR OFFICIAL USE ONLY
Chapter 3. The Reduction of the Effective Back-Scatter Cross-Sections
of Objects by 'Jsing Poorly Reflecting Shapes and Radio-
Absorbent Materials 35
1. The use of poorly reflecting shapes 35
General information on radio absorbent materials 38
- 3. Some theoretical questions
4. Narrow band interference coatings 43
S. Broadband radio absorbent coatings and materials 46
6. Measuring the char~cteristics of radio absorbent materials 51
Chapter 4. The Camouflage Properties of Terrain and Hydrometeors 53
1. The effective back-scatter cross-section of surface distributed
targets 53
2. The reflective properties of the earth's surface 55
3. The masking properties of returns from a sea s~srface 58
4. The masking action of hydrometeors 63
Chapter 5. Artificial Radar Reflectors and Their Applications 67
1. General information 6~
2. Dipole refl~ctors 69
3. Corner reflectors
4. Luneberg lanses 92
5. Passive antenna arrays 96
6. Guided missiles - decoy targets 104
7. Antiraddr eamouflage for ballistic missileF 107
Bibliography 113
1
- b -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR ~FFICI~,L USE ONLY
~nnotation
[TextJ Basic infor,nation is given on ti?e techniques and tools
af antiradar camouflage for military and industrial facilities.
- The reflective properties of radE:� targets are treated as well
as ways of r~ducing the radar visibility of vaz~ous o~jects, the
camouflage properties of terrain and hydrometeors, ar.d distract-
ing and masking false targets. Experi.mental methods of determin-
ing effecti:~e back-scatter cross-sections are described.
Along wi.th theoretical questions, considerable space is
dEVOted in the book to the dascription of specific samples of
foreign camouflage hardware and the ways it is used. The
methods and means of solving the major problems of antiradar
camouflage are consistently set forth.
The book is intended for engineering and technical workers in che
~adio pngineering specialty, as well as for military readers
interested in questions~of radio camouflage.
Same 5 tables, 87 figures and 45 bibliographic citations.
~ Table of Contents
Introduction ~4~ �
Chapter 1. The Reflective Properties of Radar Targets [7]
1. The effective back-scatter cross-section ~7~
' 2. Amplitude fluctuations of returns and the radar cross-sections of
targets ~1'~
' 3. Phase front fluctuations of a return L20~
; 4. The polarization characteristics df a return ~22J
S. The effective target cross-section in the cas2 of diversity
(bistatic) radars ~~4~
- 1 -
- FOR OFFICIAL USE nNLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
6. The average values of the effective radar scatter cross-sectiun of [2~]
real targets
Chapter 2. E~:perimental Studies of Effective Target Back-ScatteY ~29~ .
Cross-Sections
1. Methods of experimentaily studying the effective radar cross- ~29~
section [31]
2. Specific features of electramagnetic simulation
3. Measurement systems for the study of effective radar cross-sections ~34]
with models '
4. The RATSCAT facility for the measurement of the effective radar ~41]
cross-sections of various objects
Chapter 3. The Reduction of the Effective Back-Scatter Cross-Sections
of Objects by Using Poorly Reflecting Shapas and Radio- ~44]
Absorbent Materials
[44]
1, The use of poorly reflecting shapes ~48~
2. General information an radia absorbent materials [50]
_ 3. Same theoretical questions [55]
4. Narrow band interference coatings [59]
- 5. Broadband radio absorbent coatings and matexials
6. Measuring the characteristics of radio absorbent materials [65]
Chapter 4. The Camouflage Properties of Terrain and Hydrometeors ~68J
1. The effective back-scatter cross-section of surface distributed [68]
targets ~ [
2, The reflective properties of the earth's surface ~~5~
3, The masking pr~perties of returns from a sea surface [80]
4. The masking action of hydro~meteors
Chapter 5. Artificial Radar Reflectors and Their AFplications ~85~
[85]
1. General information ~87~
2. Dipole reflectors ' ~97~
3. Corner reflectors [115]
4. Luneberg lenses [121]
- 5. Passive antenna arrays [131]
6. Guided missiles - decoy targets [136]
7. Antiradar camouflage for ba~.listic nissile~
[143]
Bibliography
Introduct ion
The rapid development of radio engineering and radio electronics has necessitated
a transition in military affairs to fundamentally new techniques of weapons
utilization and reconnaissance in enemy territary. One of the major mea.ns of
target~detection and recognition, as well as for the guidance of ones own wea~,ons
- 2 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
an the target is radar. Radars and radar systems make it possible to determine
the coordinates of military, industrial and defense installations of an enemy at
lor:g range, r~gardless of the visibilYty conditions.
Almost from the very first days when radar appeared and in the course of its fur-
ther development during the Second World War, means of counterin~ the effect of
enemy radars were also being developed. A new special field of radio engineering
appeared: electronic countermeasures. At the present time, the goal of electronic
countermeasures is not only the suppression or reduction of the effectiveness of
the~means of radio co~unications, radio navigation and radar, b ut also fire control
facilities, primarily missile guidance systems. Under modern conditions, where
radio electronics is the major means of combat equipment and troop guidance, skil-
fully set up electronic countermeasures can in the final analysis significantly re-
~ duce the combat capability of the enemy and boost the effectiveness of one's own
forces and equipment.
Antiradar camouflage is one of the major methods of reducing the effectiveness of
enemv radar facilities in the overall set of electronic countermeasures. Its basic
function is to render difficult or to completely preclude the possibility of detec-
tion of military, defense or industrisl facilities by means of radar equipment.
In refining their means of attack, the military specialists of the imperialist
states take into account the fact that the Soviet Union possesses everything neces-
- s~ry to deal a shattering blow in reply. For this reason, they also devote great
attention to the design of new equipment and the refinement of techniques for anti-
radar camouf lage. This attention is explained not only by the necessity of con-
cealing their own military and industrial installations frum an answering strike,
but also by the striving to assure the suddenness of the use of weapons of mass
- destruction.
The considerable increase in the detection ranges of various targets, the improve-
men*_ in the precision of the determination of their coordinates, the automation of
the processes of obtaining and processing the information as well as the increase
, in the noise immunity and operational reliability of modern radar equipment have
made it a considerably more complex matter to realize antiradar camouflage and have
~ expanded its areas of application.
An especially large amount of work is underway abroad in the field of antiradar
camouflage for the means of air aCtack, primarily ballistic missiles. Thus
for esample, a draft budget of the U.S. Department of Defense in 1966 provided for
allocations amount to 168 million dollars for the development of ineans to facili-
tate the penetration of ballistic missiles through an anti-ballistic missile system
(ABM) of an enemy. The basis of such hardware is antiradar camoufl.age.
An attempt is made i.n this book to generalize and systematize information on the
means and methods of antiradar ca~ouflage based on data from the foreign press.
Along with the analysis of the operational principle and design of in~ividual means
of camouflage as we11 as the principles of their utilization, specific samples of
~ foreign antiradar camouflage hardware are described.
- 3 -
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/42/09: CIA-RDP82-40850R000400470041-5
FOR OFFICIAL USE ONLY
The methods and means of solving the major problem~ of antiradar camouflage are
logically presented in the book; these consist in reducing the radar contrast of
- the object being camouflaged down to the level of the ambient background; creating
an artif icial masking false target of consi4erable extent on the radar screens,
having a return intensity much greater than the returns from the target beiz~g camou-
flaged; disorienting an observation and fire control radar system by means of false
distracting targets.
The book is inten.ded for engineering and technical workers in the radio engineering
speciality. Same of the chapters of the book which contain descriptive material
and examples can be of interest to a wide circle of readers.
The author would like to express his gratitude to lecturer and candidate of the
technical sciences, V.T. Borovik, candidate of the technical sciences, I.S.
Luk'yashchenko and A.D. Trofimovich for assisting in the work on the book.
CHAPTER I. THE REFLECTIVE PRUPERTIES G~F RADAR TARGETS
1. The Effective Back-Scatter Cross-Section
One of the constant (though still insufficient) conditions for providing effective
antiradar camouflage for protected objects is the presence of the most complete in-
formation on the quantitative and qualitative characteristics of the reflection of
electromagnetic ener.gy from various targets.
When electromagnetic energy impinges on any object (a target), electrical curren*_s
appear at its surface, if the target is a conductor, or electrical charges, if the
target is a dielectric. In this case, the target itself becomes a source of elect-
romagnetic emissions. The energy of an electromagnetic wave incident to a target
is scattered in all directions. The portion of the energy reflected from a target,
which arrives at the input to a radar receiver, forms a target marker on the radar
screen. The level of the signal reflected from the target depends on the radar
parameters, the electromagnetic propagatior. conditions and the nature of the tar-
_ get: dimensions, configuration, irradiation angle and electrical properties of the
; target material.
A conventional quantity is used to quantitatively evaluate the reflective properties
_ of any radar target: ot - the effective target back-scatter cross-section (EPRJ.
As is well known, the secondary emission power, P2 (the energy scattered by a target
when an electromagnetic wave impinges on it), is directly proportional to the flux
density of the energy, II1, irradiating the target, i.e.:
� (1.1)
p2 ~t~l
- The proportionality factor Qt in formula (1.1) is called the effective back-scatter
cross-section. Since the majority of radar target~ have the property of directional
second�ary emission, taking into account the dir~ctionality factor of the reflecting
object, D, which characterizes the degree of concentration of the scattered power
- 4 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
in the direction to the radai, the expression for Qt can be written in the follow-
ing form [2]:
Qt = (P2/iIl)D (1.2)
~u~ ~t ~ m2 . . .
~o 000
sooa ~e effective back-scatter cross-section can
4 000 -
_ _ _ - , be expressed in units of area (m2) or in
Zoov - - decibels (dB), where at [dB] = 10 logat [m2],
~ooo - - i.e., a level of zero decibels corresponds to
= 500 ~ - - a value of Qt of 1 m2 (Figure 1.1) .
4~~ _
It can be seen from f~rmula (1.2), that to
zoo - - determine the effective back-scatter cross-
roo - section of a target, it is necessary to know
60 - - the energy f lux densities at the points where
. ti0 - the target and the radar antenna are located.
The derivation of theoretical data on the field
20 - - -
of t:~e reflected wave, and consequently, on
_ ro - the effective target cross-section reduces in
6 - practice to the solution of ~faxwell's equation.s
4 _ with the appropriate boundary conditions. The
~ Z _ _ methods of solving such equations which exist
~ - - - at the present tim~ allow only for the calcula-
~ tion of the effective back-scatter cross-sec-
~ 0 lU B 20 JO 6u,B6
- tion of bodies with a simple geo~aetric shape
; (Table 1.1) .
Figure 1.1. Graph for the con-
~ version of effective Objects with a simple geometric shape are
I back-scatter cross- encountered rather rarely under actual radar
j section measurement detection conditions. As a rule, they have a
;i units. complex configuration and consist of a large
i number of elemenzary reflectors. Examples of
, single targets with a complex conf iguration
~ ships, aircrafts, missiles, various ground structures, etc. Several individual
objects, located within the bounds of the reflecting volume (Figure 1.2) at
relatively large ranges as compared to the radar wavelen~th, form a group target.
It can be seen from Figure 1.2 that the dimensions of the reflecting volume with
respect to range are governed by the quantity (cz/2) (c is the propagation
velocity of the electromagnetic energy and T is the radar pulse width), and with
respect to the angular coordinates by the linear dimensions of the beam of the
radar antenna at the O.S power level (6aZ9elev~�
An overall set of reflecting elements, arranged relatively close together and
occupying a comparatively large region of space, forms a so-called vlume distri-
buted target. Hydrometeors, a cloud of dipole reflectors, etc. can be numbered
among such targets.
- S -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFF'ICIAL USE ONLY
~ TABLE 1.1. Formulas for Calculating the Effective Back-Scatter Cross-Section
of Geume~ric Bodies
Spher
For a~~ a QnN en~imn~ ~f~
b~ - tt!!i
For a wavelength g�
Ijpi~ nnNne e~~nnM ~ ~ n:
144k'a'
. . .
Circular C~linder
� Kpyrna u~~n?+enp
~ B rsln (k~, cns 9) 1', .
en = k~1L'sln A I k~, cos A
I ~
~ , . .
s,~ r kAG' npo 8~ 2 ~
, � ~
, . � ' 2a
, . k ~ - eonHOece ~~ncn~.
. is the wave ntmmber.
� Cone
~ � � KoNyc
i c+c ~ e~ a af~ 1R' a. ~ ~ '
' ; r' HanpaeneNee obny'ICHIIN CO6pA4~CT C O~biO
~i~ Kot~gca , .
. 1 fip~IMOyronbnea nnacrH1Ha ~
. Rec a~n~ular }~�at
~ a sl~t s~n 8 coa ~1 X
f! aq ~ ~1R 0~'~'!! ! 11 CQf t J
. � d ~ ~
- ,In (kb cos e) �
~ e X~ ~
~ 11pN~iopMaabNOw naneuHe ~ nnocaocre nnacTNNd: '
a~b'.
v4 D 4+c .
- 6 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R000440070041-5
FOR OFFICIAL USE ONLY
[Table 1.1, continued]:
Flat Disc
. finocK~~tl AHCK
_ b- o, _,ck'n' sln' 0[~' ~2ka Cns 8) I~
~ ka cos 9
; ( ~ rne J~ -~yuKUt+A 6eccenn I�ro nnpaaw~. ( 3'
~ ~
~ ~ IIpN ~opManbiloM naAen?~n K nnaxocrN AHCKa:
. q~~as
~ ~ 0, s .'-T-
~
Dihedral i,orner Reflecto '
Aey~PeNp~n yronKOed~
' oTpa~caTenb '
_ h 8+c (aff)~
� q ~
� '
B MaRCNNy M2 J~H~~p~NM61 ()ACCCANNA
at the back-scatter pattern maxi ~
TTpeed paNHbp y~oneicosenidfor
orpaHCarenb
12na' ~ ~
_ -fl~ ?
e waKCnMyMe p.earpa~?~+ pxceAxua
at the back-scatter pattern maxim
Key to Table 1.1.:
1. The direction of irradiation coinci3es with the axis of the cone;
2. In the case of normal incidence to the plane of the plate:
3. Where Jl is a first order Bessel function. In the case of ~iormal
' incidence to the plane of the disc:.
~ ~
~
V"'
R -
Radar PnC cK -
~1
- Figure 1.2. The reflecting volume V=(n/4)R26(cT/2).
If the individual reflecting elements merge into one comparatively thin layer, then
they form a surface distributed target. Such targets can be encountered in the
radar scanning of a ground or sea surface. 'The reflective properties of volume and
surface distributed targets are treated in Chapter 4.
- 7 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
T'.ie calculation of the effective target cress-s~ection of actual targzts with a
complex c~nfiguration presents great theoretical difficulties. Computers find
widespread application in the analytical determination of the effective back-
scatter cross-section of actual objects.
At the present time, the effective cross-section of reflecting objects with a
complex shape is studied primarily experimentally, using special equipment and
hardware.
- The following are included among the new trends in the study of radar returns:
--The study of electromagnptic energy scattering by space bodies and vehicles, as
well as by plasma formations;
--The synthesis of objects with specified secondary emission characteristics;
--The determination of the effective cross-section of objects in the case of
broadb and system operation with a high resolution;
--Finding the scattering characteristics at millimeter and optical band wavelengths;
--Determining the effective cross-section of distributed objzcts for the purpose of
recognizing them.
~ 2. Amplitude Fluct�ations in Returns and the Effective Back-Scatter Cross-Sections
of Targets
A complex target can be treated as the aggregate of a large number of elements
which scatter the electromagnetic energy in various directions. Such elements can
be: the convex portions of the target which are characteristic "shining" spotsT
flat areas, which produce a mirror or diffuse reflection. The individual s~ruc-
tural components of a target, the dimensions of which are commensurate with the
wavelength, will produce intense secondary emission because of res~nance phenamena.
The overall amplitude of the reflected signal will be governed by the relative
phases and amplitudes of the signals reflected from the elementary secondary
radiators. The amplitudes of the individual signals which have diff erent phases
at the reception point either add together, thereby providing for a large total
~ return, or have su~h ratios that the signal is either partially or completely
suppressed. As a rule, the spacing between the individuai reflecting elements
considerably exceeds the radar wavelength. In this case, the phase of the signals
at the receive point will change with a change in the position of the target
relative t~ the direction to the radar, something which in turn will cause addi-
- tonal fluctuations in the return and the effective cross-section of the target.
In order to ascertain the mechanism for reflection from a complex target, we shall
initiall consider a target consisting of two equal isotropic reflecting elements,
spaced a distance Z from each other (Figure 1.3), whsre:
Z < cT/2 ,
- 8 -
FOR OFF[CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
where c is the speed af light; t is the radar pulse width.
'The overall voltage of the signal reflected from such a target will be equal to
the following at the input to the radar receiver [2]:
uin~ uex = Umi ~u~ - Um~ ~CC~'t~~ -
Here, Uml and Um2 are the amplitudes of the voltages of the reflected signal from
the first and second tar~ets; ~1 and ~2 are the phase delays of these voltages,
equal to:
4xR
-~j~~ ~'"~o~~
where �pl and ~02 are the phase changes with reflection.
If the effective radar cross-sections of the first and second targets are equal,
then U~1 = Um2 and consequently,
' u, s Up~- 2U~/~ CO$ C~ ~fOt -'T~' J~ .
~n ~
' where �p and are the difference and sum of the phases of the voltages U1 and U2.
; If ~O1 - ~02~ then:
~
~ 2R 4ni
~ = 2 ~R, - R!) ~ _ ~ ~o~ a.
i
Then the amplitude or the reflected signal voltages'will be equal to:
i ~ '
C ~af `
i Um= 2Um~ COS ~ ~os e~.
I
I, Or, by converting to the total reflected signal power, we obtain:
I P~; = 4P, cos' C~ cos el,
~
where P1 is the reflected signal power from one isotropic radiator.
Since the power of the return and the effective radar cross-section are related by
a linear function, one can write that for two elementary targets, the effective
radar cross-section will be:
2a!
0~ ='~O~ COS� COS O , ~
\ (1.3)
where Q1 is the effective cross-section of one isotropic radiator.
- 9 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
It can be seen frvm expression (1.3) that with a change in the wavelength a and
_ the angle 9, the quantity v2 can take on any value from zero to the maximum, which
is f our times greater than Q1 (Figure 1.4).
a� � o.
~ .
t
1 2
i ; i~ 270'- 1 J 4 a~ 270' 7 J 4 al
% B ~
~ ~
- ,~2~~~ a ~ Q~ � ' ~ ~ ' ~ ~ . , '
i : ~80� ~BO� '
i ~ L=1x
i p�
~ ~
~ ~ � , ~ ~ ~ ~ ,
.
~
170'- T 3~-6
Figure 1.3. A campiex target
consisting of two �
scattering elements ~ . ~ , , , � ~ , ~ .
- elements with a ~'4~ ~
_ spherical shape. Figure 1.4. Polar plots of the function
Key: 1. Radar; QZ/ol for various values of
_ 2. Scattering elements. Z/a and the angles 6.
Real targets consist of a set of scattering elements with different reflecting
- properties, where each of these elements can additionally interact with the others.
The mutual motion of the target and the radar, as well as the motion of individual
elements of the target itself (for example, as a result of the natural vibrations
of the aircraft o~ ship) exert a great influence on the nature of the flucutations
. in the resulting return. It can b e seen from Figure 1.5 that slight changes in the
heading angle of an aircraft can change the instantaneous value of at by a large
amount.
The amplitudes of the returns and the effective back-scatter cross-sections of
~ complex real targets are subject to random f luctuations. Consequently, the tech-
niques of probability theory must be employed to characterize these~quantities.
- They can be sufficiently completely described by the distributions and the spectr ~n
of the fluctuations or by an autocorrelation function.
Let a complex target (aircraft, sh ip, ground structure), consisting of a set of
arb itrarily arranged reflectors, contain an element as part of it which yields a
- stab le reflected signal ("shining" point), the amplitude of which exceeds the
total signal from the other elements. The amplitudes and phases of the returns of
al? of the other elementary reflectors will vary (in contrast to the "shining"
- point) as a function of the mutual motio~� of the *.arget and the radar.
- 10 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLV
' The ~esulting signal from such a target
~.aill be deter~nined by the expression:
, ` ~ ~ ~
~
~ ~ n
~ ` ~
F-Acosc~t-}-L EMCOS~W(-q~~.
~ ' k_i
~ where A is the amplitude of the
"shin~.ng" spot signal;
E~ is the amplitude of the k-t h
' ~ ' element signal;
~ ~k i;s the phase shift of the
~ ' k-th element.
~
With a change in the relatiue pasition
~ of the radar station and the target,
the ranges to the elementary reflectors
Figure 1.5. The effective back-scatter and their effective cross-se,ctions will
c.ross-section of a twin also change. This leads to random
engine B-26 bomber as a changes in the amplitudes (Els E2,
~ function of azimuth. The Ek) and the phases (~1, ~2, ~k) of
measurements were made at the reflected signals. As was demon-
a radar wavelength of strated in paper [1], the two-dimen-
a= 10 cm. sional probability distribution of the
quantities E and ~ for the composite
signal can be described by the equation:
E G�' ~1' - 2AE cos Y l (1, 4)
W~E. q~ ~ 2RY~ CEP L- rZY~ ~ r .
where v is the amplitude dispersion.
In order to determine the probability density of the random resulting amplitude E,
we integrate expression (1.4) over all possible values of the phase � from 0 to 2~r:
Zr� "
, ~IE~aJ ~\G~ t~u~~
D
2�
r f f r
exp i-~-, 2a ~ exp I~� coe t 1. ~ 1. 5)
, L ~ l J
It is well knawn that: zR '
~ ( AF / A~ 1.
2a ~ exp L cos p~ Q, = J. J
� o (1.6)
- 11 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
F~DR OFFICIAL USE ONLY
where J~(AE/v2) is, a zero order Bessel function of an imaginary argLm?ent.
We derive~the following from expressions (1.5) and (1.6):
E r E~+A~ ~E (1.7)
1~~E)='~expl- 2~, ]J; ( y, .
o ~
Equation (1.4) is called the generalized Rayleigh distribution. If A= 0(there
is no stable component), then AE
and the probability density W(E) is C~') �~�(0)1' 1
governed by a simple Rayleigh distribution:
. `
I~ (E)~: ~ exP 2 1. (1. 8)
J
~
_ Expressions (1.7} and (1.8) can be written in a more general form, if the following
symbols are introduced: .
~ ~i C dE
a=~ iu= du= y. ,
Then:
~ = o exp r -�t Z n~ ~ .1� (a~~).
l
_ , ,
lY(u)~~vexp~-,2
L
Curves for the distribution W(v) are shown in the graph (Figure 1.6), which were
plotted for various values of the constant component of [1]. It can be seen from
the graph that for large values of the stable component a, the distribution of
W(v) approaches a normal distribution. If there is stab le component (a = 0), the
resulting signal is produced as the simm of solely the signals from the random
reflectors. The mezn relative value of this signal will be equal to:
~ ar0 t
'v~Jvexp~- 2 ~dv~~ 2 .
l.
0
The dispersion of the relative signal amplitude is:
_ (-~-2- 2 �
~3y converting fram the value E in expression (1.7) to power P, we derive:
- iz -
FOR OFFICIAL USE ONLY `
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR ~FFIC[AL USE ONLY
Y~ L p~. p, J [ 21/P~ 1 (1. 9)
~P) = i exP - ~ ,I� ~ J~
where P~ = A2/2 is the power of the stable signal component; P= E2/2 is the power
of the resulting signal, dissipated in a resistance of 1 ohm.
We shall introduce the symbol:
wluJ Q,o
~'S ~ 2 S p~ R,
0,4 rrt = y, = 2 � (1.10)
0, 3
~Z Then the average po~~er of the return
will be equal to:
0 i ? S 4 S 6 ~ u=T
, P=v2+P~
Fi~ure 1.6, Curves for the distribution
of the resulting signal
amplitudes. or, in other words:
~ P
"t=~ }.m~~+a�' (1.11)
2
Taking expressions (1.10) and (1.11) into account, we write expression (1.9) in
the form:
[V (P) _ ~ ~m exp r- m - ( I r;- ne) ~ ~ X
l
XJ� [21' ~(I+m)~J�
~ Since the effective b ack-scatter cross-section of the target, c~t is proportional
to the pow er of th e return, then:
~~�a) Q~ eap I- rn ~-f m~ en J X
~ (1.12)
0
XJ. [2 nt(I m) a-�
q
~ If there is no stable component (m = 0), then the random quantity corresponding
to the effective cross-section of the target, is distrib uted exponentially:
~~aa~~n_f = aq exP I_ on 1~ ~ 1.13~
J
- 13 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPR~VED F~R RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFfC[AL USE ONLY
where at is the resulting effective radar cross-section of the target; crt is the
mean value of the resulting effective radar cross-section of the target.
In e;cpression (1.12), the parameter m can be treated as the ratio of the eff ective
radar crc~s-section of a stably reflecting element, Qtp, to the average _ue of
the effective cross-sections of all of the random reflectors, atE. t'h=~., :~r the
relative effective radar cross-section, at/Qt, the distribution densities (1.12)
and (1.13) will assimme the following forms:
lV( ~q~ -(I -{-m)exp~-m-(I -}-in) ~n ~X
\ ~n L ~n
x~� ~2 ~ } !n, ~ n 1
/ 4
7~ P 0q1
~ C �n = CJt - an ! � ,
1
The curves for W(Qt/at) are de~,icted in Figure 1.7 as a function of ot/Qt for
various values of m[1]. Using these graphs, one can estimate the probability
of the appearance of various values of effective target radar cross-sections.
W (~4)
m =J0
t
m=o ~ Figure 1.7. The effective radar cross-
0,8 m=s,3 section distribution of a
. m~l , complex target.
O,q ' _
. , Key: Ordinate = W(ot/at)�
0 0,3 r,o ~,S t.o t,~ ~
a
As a rule, the spectral and correlational characteristics of returns, the auto-
correlation function and spectrum of the signal, are used to ciescribe ~he fluctu-
ation variation in the amplitude of the reflec~ed ~ignal and the eff ective radar
cross-section of the target as a function of time.
The statistical relationship between the values of the fluctuating voltage E,
broken down into a time interval T, is decsribed by means of the autocorrelation
function R(T) :
r
R(t) =11m T` G(t) E(! t) d1,
T-.ao
0
where T is the observation time.
- - 14 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2447/02/09: CIA-RDP82-44850R444444474441-5
FOR OFFICIAL USE ONLY
The maximum value of the autocorrelation function will occur when r= 0. The
value of R(T) will fall +~ff in step with the increase in i. The duration of an
observation T should be cfiosen so that all of the characteristic fluctuations
in the function E(t) are encompassed.
The autocorrelation function is closely linked to the signal fluctuation spectrum.
If the changes in the amplitude of the fluctuating signal take the form of a steady-
state random process, E(t), in a specified time range of -T < t< T, then the fluctu-
ation spectrtmm is dete nnined by the relation:
r
~~1)= f ~~~)e-~R~~dl.
-T
_ while the spectral density is:
~ ~O = llm 2T
r-.~o
If E(t) is the voltage across a resistance of 1 ohm, then G(f)df is the average
power dissipated in a 1 ohm resistor in a frequency range of from f to f+ df,
while G(f) is the average power density, having the dimensions of power per unit
bandwidth.
The following relationships exist between the spectral density and the autocorre-
lation function:
~
Q(!) = 4 S R(t) cos 2n(i d~,
0
~ ~
R(t)= ~ G(() cus 2n js dJ.
. o
The probability distributions of the effective cross-sections of real targets
and the nature of the change in the effective cross-sections as a function of time
' are usually determined experimentally.
3. Phase Front Fluctuations of a Return
For a complex target, there are also fluctuations in the phase front of the
signal along with tha fluctuations in the amplitude of the reflected signal.
To explain this phenomenon, we shall again turn to the target model consisting of
two point isotropic radiators and compare the pictures of the phase fronts of this
target and a single isotropic radiator (Figure 1.8).
The equal phase surfaces of a single point radiator will be concentric spheres
with the center in the radiator. For a two point target, these surfaces will be
. other thanspherical. TEie quantity which characterizes the bending of the phase
- 15 -
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFF'ICIAL USE ONLY
front can be found as a function of the angle d between normals to the equal phase
surfaces of the single point and two-point radiators for various emissian angles
o i Figure 1.8. The phase fronts of a single point
~ ~so isotropic radiator and a tatget con.-
Z , sisting af two isotropic radiators.
~ ~a
~ Key: 1. Equal phase surface of the twc-
point target;
2. Equal phase surface of the
single point radiator.
~E
.
y Figure 1.9. On the determination of the phase shift.
y
~ ~ t
: '~f
: ~ '
D /
d
P/?C R~dar
Let the radar be located at remote point B(Figure 1.9). Then the fxequency
incoming from point 1 will lag in phase the frequency from the single point source
by an angle of:
- 2+c t .
R = ~ Z Slil
while the frequency incoming from point 2 will lead it by the same angle. If the
amplitude of the transmitted signals are E and kE, where k< 1, then the vector
diagram will have the form shawn in Figure 1.10a. The resulting vector of the
two point target field will be equal to the sum of the vectors E and kE. We
f ind f rom F igure 1. lOb : tg ~_E sin kE sIn _
E cos s}- kF. cos
=1g~ ~ +k.
a=arctg (e ~ +k).
\
Calculating the value of d for various values of k and Z, one can construct .
- the picture of the ~;hase fronts of a two point target (Figure 1.11). The fluctu-
ations of the phase front because of the continuous motion of the target relative
to the radar are of a random nature. These fluctuations are manif est at the output
of the receiver in the form o.f random changes in the error signal for the measure-
ment of the angular position of the target, and for this reason, they are frequently
called angular noise.
- 16 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400074441-5
FOR OFFICIAL USE ONLY
F E
, ` ~ kf~tn~
g NanpcQntNUe/ E 6 EStnE
- u~nyvenu~
~ ~ ucmOvNU
a~ . EtOS6 kEco~f tl
,tf 6)
a)
Figure 1.10. Vector diagrams of the field of a two-point ~
target.
~ey: 1. Direction of the emission of a single
- point source.
Figure 1.11. Equal phase surface cross-sections in the
_ plane of the drawing. Target point 1 is
the source of large amplitude oscflla-
~ 1 tions [lJ . .
U
- i
I . 4. The Polarization Characteristics of a Return
3/lP, Effective
86 Back-scatter
I ~ Cross-sec~ion ~
40 - ~
,
i . ~ ~ ~ 1 ~ �
~ ~,~p ~ ~
i ~
~
!n ~ ' ~
i 1 _ , ~ ~~,~i ~~.i
, ~ ;,1 t ~
. .
J~
0 40 80 120. 160
~~nMynr, :vos Azimutfi, degrees
Figure 1.12. Experimental diagram of the effective radar cross-section
of an aircraft as a function of azimuth, measured in the
- plane of the wings.
Key: 1. Vertical polarization of the incident wave;
- 2. Horizontal polarization. Frequency of 75 I~iz.
- 17 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
' T~,BLE 1.2 Results of Measurements of the Losses of a Radar Signal Reflected
From an Aircraft (n = 10 cm)
_ Incident Wave Target Changes in the Reflected Signal Losses,
Polarization dB
Plane Ideal Reflects all of the energy; ~
the polarization plane of the
reflected signal is parallel
to the polarization plane of
the incident wave
Plane Air- A portion of the energy 0.5
craft (-10 dB) is returned with
transverse polarization and
~ is attenuated by the recei.ver
Circular Air- The reflected energy is split 3
(reception craft equally between orthogonal
with the same circular polarizations
polariza*ion
as the trans-
_ mission)
Experimental studies confirm the dependence of the ref lected signal intensity, and
consequently also the value of the effective radar cross-section of the target on
the kind of polarization of the transmitted signal (Figure 1.12). When electro-
magnetic oscillations are reflected from any object, the polarization of the
reflected wave doesnot match the polarization of the indicent wave in the general
case, i.e., the reflec~.ed :;ignal is depolarized. The degree of depolarization
depends on the properti~~s of the irradiated target and on the polarization of the
ineident field. Solids exist which reflect any polarization field without distor-
tions: these are a sphere and a flat disc, irradiated in the direction of the axis.
Another extreme case is a target which produces a reflected f ield with one polar-
ization for any polarization of the incident wave. Such a target is a fine wire.
Objects of an arbitrary shape change the polarization of the incident field in
various ways; in this case, attenuation of the signal is observed a a rule at the
input to the receiver because of the depolarization (Table 1.2) [44J.
S. The Effective Back-Scatter Cross-Section of a Target for the Case of
Diversity (Bistatic) Radar
In bistatic radar, the transmitter and receiver are located in different places.
A separation angle S is formed between the transmitter-target direction and the
receiver-target direction (Figure 1.13). If 0�, bistatic radar reduces to
the conventional monostatic case. .
- 18 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
F(3R OFFiCIAL USE ONLY
Uee~ ~
Target
. a
9+.
d
r
. ~ ~
, . . . . .
(IepCdamYUlr ~1DVfMNUk
iransmitter Tteceiver .
Figure 1.13. Radar using a spatially separated transmitter
and r~ecei,ver.
The range equation for bistatic radar has the following form:
I'~~er/�~aGnv~'Oae
m
Prec . (4a)' DiDzLo �pLp ~~p ~
wliere P~p is the received signal power;
~ PH3n is the transmitted signal power; ~
i GN3n is the directional gain of the transmitting antenna;
I
G~P is the directional gain of the receiving antenna;
Qu6 is the eff ective target back-scatter cross-section;
~ D1 is the distance from the target to the transmitter;
~ D2 is the distance from the target to the receiver;
~ LP ~eP are the radio wave propagation losses from the transmitter to the
~ target;
i
~ LP ~P are the radio wave propagation losses from the target to the receiver.
~
' In this case, Qu~ is a measure of the energy scattered in the direction of the
receiving antenna.
As has shown in the literature [28], for separation angles 6~ 180�, the relation-
ship between the values of the eff ective radar cross-sections for the case of
monostatic and bistatic radar can be found if the follawing theorem is employed:
"At the limit, in the case of an infinitely small wavelength, the effective target
cross-section, where the target is a sufficiently smooth solid, for the case of
a diversity (bistatic) radar station with di.rections to the transmitter and the
receiver determined by thE vectors k and n respectively, equal to the effective
- - 19 -
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOii OFFiCIAL USE ONLY
target cross-section in the case of a cambined (monostatic) radar_station, where
the direction to the transceiver is determined by the vector k Y n, where k~ n)."
Here, k is a uni~ vector directed fram the transmitter to the target, while n is
a unit vector directed from the receiver to the target.
It is apparent that in those cases where the effective radar cross-section of a
complex target is composed of the effective cross-sections of several elemPnts,
- the transition from the bistatic to the monostatic case is accompanied by a change
in the relative phases, and consequently, in the fine structure of the effective
cross-sectuon pattern of the target. It has been determined that when the effect
of shading is taken into account and when the angle is limited to a certain range
of values, the indicated theorem can be successfully ~ployed. The inf luence of
shading effects for a large aircraft is shown in Figure 1.14. It can be seen from
the figure that in the case of bistatic measurements (S = 135�) the engines and
fuel tanks an the wings of the aircraft prove to be~"in the shade", while ln the
case of monostatic measurements, the reflections from them considerably increase
the effective radar cross-section of the aircraft.
i
i
i
i
i
i �
i i
~
Transmitt
I?e eaamvuK Receiver
. ~=IJ5�) ~
/Ipu~nMUK
(p.1J5')
Transmitter neo~aom~~~
& receiver~ "0"~'""ux (p=o�)
Figure 1.14. Electromagnetic energy scattering by the nose section of
a large aircraft for two values of the separation angle.
It was found when comparing the results of monostatic and bistatic measurements
using this theorem [28], that the maximum values of the effective cross-section,
as well as the limits of variation in the effective cross-section obey the theorem
with sufficient precision even for relatively large wavelengths. This can be seen
from the graph of Figure 1.15a and 1.15b, in which the results of ineasuring the
effective radar cross-section of the large aircraft depicted in Figure l.].4,
shown. During the measurements, the transmitter and axis of the aircraft were
located in the same plane and the angle 6 was read out from the axis of the air-
craft (frtim the nose) to the bisector of the angle formed by the transmitter,
target and the receiver.
-20-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400074441-5
FOR OFFICIAL USE ONLY
6q 86 .
~ ~ ot , dB ,
1
VO
30 y 4
TO - _r 1
'O ~
Q 6V Q ~8Q BO
a) ( a)
er4.d6 vt, dB
5D
40
- ~ ~ 1
30 ' ,
~ '
20
~ 4.
?0
p 60 - r2o ~80 'Y
6) (b)
Figure 1.15. The effective back-scatter cross-sections of a large
' jet aircraft, measured at a frequency of 250 MHz for the
case of horiaontal polari2ation of the incident wave.
Key: a. Medians (every ten degrees);
b. Maximum values (every ten degrees);
i. s = o�;
2. s = 30�;
3. N a 6~~i
4. ~ = 135�.
The theorem considered here is not applicabla to the case of s= 180� (forward
scattering). In this case, the effective radar cross-section of the target can be
many times great~r than for a monostatic radar (back-scattering). In the case of
forward scattering, the effective radar cross-section of the target (if the wave-
length ~ is sma11 as compared to the target dimensions) will be equal to:
Qtf = 4nA2/a2,
where.A is the target projection area.
- 21 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R000440070041-5
FOR OFFICIAL USE ONLY
A sphere of radius a has an effective target cross-section for a monostatic radar
station of at = na2. Consequently, the ratio of the effective cross-sections for
the case fo forward and back-scattering for a sphere is equal to:
eQ~ 2+~a '
ae ~ 1 .
\ /
When a/a = 10, the theoretical effective radar cross-section of such a targeC in
the case of forward scattering is 36 dB greater than for back-scattering.
6. Average Values of the Effective Back-Scatter Cross-Sections of Real Targets
The ccean value of the effective cross-section Qt, is usually employe~ in the
practical estimation of the range of a radar. This quantity can be dervied by
averaging the values of Qt for various di.rections of the incident wave.
TABLE 1.3.
Average Values of Effective Back-Scatter Cross--Sections
Effective
Radar Target Cross-2ections,
m
Nose cone of a ballistic missile ~�2
Fighter 3 - 5
Medi~ bomber 7 - 10
~,ong range bomber 15 - 20
Transport aircraft up~to 50.
Cruiser 14,000
Low tonnage transport 150
Medium tonnage transport 7,500
Large tonnage transport 15,000
Trawler 750
- Small submarine on the surface 140
Launch 100
Submarine conning tower 1
0.8
Man
Average values of the effective radar cross-sections of various real targets
are given in Table 1.3, which were obtained as a result of the statistical gen-
eralization of a large number of ineasurements at centimeter band wavelengths.
As a rule, the maximum detection range of such targets was measured, RmaX, and
- then Qt was determined from the basic radar equation.
-22-
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
- FOR OFFICIAL USE ONLY
.
CHAPTER TWO. THE EYPERIMENTAL STUDY OF THE EFFECTIVE BACK-SCATTER CROSS-SECTIONS
OF TARGETS
1. :fethods of Experimentally Studying Effective Back-Scatter Cross-Sections
If the atm.ospheric absorption of electromagnetic energy, ground or sea returns and
other limiting factors are not taken into account, then radar range in free space
- is determined b;~ the formula:
Rm~ _ A~ 4Q
~ (2.1)
where A is a factor which combines the radar parameters.
It is app~rent th at the basic method of reducing the radar detection range for an
object to be protected using antiradar camouflage is the.reduction of the value of
the effective rad ar cross-section of such an object. The successf ul resolution
of this problem not only reduces the detection range of the object being defended,
but additi~nally does the following:
--Reduces the target detection prob ability and the probability of autoguidance
svstems of missile armaments which use radar locking onto it;
--Allows for a significant reduction in the power of jamming transmitters installed
in the object being protected (if Qt is reduced by u factor of n, then the power
' of the jamming transmitter installed in this object to protect it can be reduced
bv a factor of n) ;
--Makes it possible to the size and weighe of ia15e rauar targetJ ~.~~hi~h sim~slate
' the actual object witn a reduced 6t;
--Boosts the camouflage effect of hydrameteors and sea and ground
, returns.
To achieve the requisite camouflage effect when protecting one military or
industrial facility or another, it is essential to know not only its overall
effective radar cross-section, but also to determine which elements of the struc-
ture specifically contribute the major share of the reflected signal. In other
words, it is necessary to ascertain which portions of the object's surface must
be camouflaged f irst of all. To obtain such data by means of theoretical research
is an extremely complex problem, and at times, even impossible. For this reason,
the major method of studying the effective radar cross-sections of real objects
is experimentation at the present time. An advantage of the experimental method
of study is the f act that it mz.kes it possible to obtain a detai?ed reflection
pattern in the elevation and azimuth planes and to ascertain the fZuctuation and
polarization characteristics of the return. The precision of the experimental
method is sufficient f~r the design of a false target which simulates the real
target with a high degr.ee of reliability. The data obtained in this fashion can
-23-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R040400070041-5
FOR QFFIC[AL USE ONLY
be utilized for the solution of the inverse problem: identification of the signal
from a real object against a background of signals and false targets.
One of the most obvvous methods of ineasuring Qt is the study of the reflecting
properties of an object under full scale conditions. It can be seen from the
radar range equation:
Prv _ G'~'a~ (2.2~
' -(4a)'R'
Prec Ptrans P�~~
That if the radar is calibrated, then the value of ~t can be calculated by measur-
ing the transm.itted and reflected powers, Ptrans and Prec�
However, the performance of such measurements in a real situation entails consid-
erable organizational and tech~ical difficulties and reQuires considerable material
outlays. For this reason, the reflective properties of objects are studied at the
present time primarily under laboratory conditions or on special test sites. Both
the objects themselves or mock-ups of them made to full scale, as well as models
of the targets being studied can be used in this case. The use of mack-ups and
models makes it possible to not only study the secondary emission pattern of the
object in detail, but also to determine the inf luence of its individual structural
components on the total value of the effective radar cross-aection and the struc-
ture of the reflected signal. The studies consisttheirereflective propertieshand
elements being studied frc~m the model,
comparing the results obtained with the reflected signal level received from the
~ model of the entire object.
2, g~�cific Featutes.of Eleetromagnetic Simulation
A model which differs from the original by a scale of n= 1/z is placed ~n the
field of the electromagnetic tadiation, the wavelength of which should be n times
shorter than when irradiating the actual target. In accordance with the require-
ments of the experiment, the model is rotated in one plane or another. Its second-
ary emission field acts on the receiver at the appropriate frequency, is converted
to an electrical signal of a definite level, which is then registered on an auto-
recorder tape, photographic film or on magnetic tape. The polar plots obtained in
this way make it possible to ascertain ~h e level of the reflected signal as a
function of the angular position of the model.
The possibility of a simple change in the scales of the electromagnetic systems
is a direct consequence of Haxwell's linear equations. It is sufficient to meet
the similarity conditions when modeling that the dimensions of the target and the
wavelength f~r the measurements be changed by the same number of times, while the
quantity E/H be the same for the model and the real object (Table 2.1).
Small models of aircraft, missiles an~ ships are turned out of an entire piece of
metal, usually, alumintmm or magnesium. Models of large dimensions are f abricated
. from wood or fi.berglass and then coated with several layers of conductive paint.
-24-
FOR OFFICIAL USE ONL~I
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/02/09: CIA-RDP82-00850R000400470041-5
FOR OFFICIAL USE ONLY
To perform measurements on B~odels, one must correctlychoose the transceiving equip-
ment, and additionally, meet the three following main requirements:
1. A plane wave should impinge on the model.
2. Clutter due to reflections fram foreign objects (walls, stands, supports, etc.)
should be minimal.
- 3. The elements for fastening the models should not have an inf luence on the
structure of the electromagnetic field reflected from it.
TABLE 2.1.
Relationships Between the Parameters of a Model and a Real System (Target)
Quantity Real Model ~
System
Length Z Z' = Z/n
Time t t' ~ t/n
Frequency f f = fn
Wavelength 7~ a' = a/n
Specif ic conductivity Y Y' = Y?7
Dielectric permittivity E = E
~ Antenna gain G G' = G
Effective back-scatter cross-section ~t a't ~ Qt/n2
i
~
~ In order for the effective radar cross-section concept to have any meaning, the
~ value of the effective cross-section should be determined and measured for a
i certain reference standard incident field. Usually, a plane wave field is
chosen as the reference standard field. An antenna radiates a spherical wave,
; and only with increasing distan~e from the radiator does the wave front approxi-
~ mate a plane front. Hawever, in step with increasing~distance of the model from
the antenna, the received energy falls off rapidly, and for this reason, this
' distance is chosen as small as possible (Rmin), but nonetheless such that the
- wave front differs little from a plane one. If the distance Rmin exceeds the
dimensions of the test site or laboratory, then a special lens is placed between
the radiator and the target to equalize the incident wave front.
- As a rule, the electromagnetic field irradiates not only the model, but also the
support on which it is mounted as well as the surrounding objects, so that the
resulting b a~k-scatter field at the receiver takes the form of a combination of
the usefu 1 fieTd from the model and spurious fields. Especially great inter-
f erence is obtained because of returns from walls when operating in closed rooms.
In order to reduce this kind of clutter to a minimum, measurements in closed
-25-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
rooms are made in so-called anechoic chambers. An anechoic chamber is created by
means of covering the walls of the room in which the measurements are made with
radio bsorb nt coatings. Free space conditions are simulated in this way.
Anechoic chambers, the fabrication and application of which have beeome possible
- because of the existence of high quality radio absorbing materials, make it pos-
sible to study the effective radar cross-sections of various targets and test
radar equipment in short periods of time with a high precision, regardless of the
weather.
Radio absorbing materials for anechoic chambers are materials which absorb radio
waves in a wide range of frequencies. For this, they are made with a"matched"
- input, i.e., the impedance of th? material at the surface is equal to the impedance
of free space and gradually increases with increasing material thickness. The
majority of samples of such materials are made from flexible or solid plastic
foam with interspersed particles of absorbing material. To improve the matching
to free space, the exterior surface of the material (coating) is made with a spine
covered appearance. Hair mats impregnated with an absorbing camposition can also
be used in anechoic chambers. For the meter wavelength band, individual pyramids
made of absorbing plastic foam are produced with a height of about 2 m. The radio
absorbing materials employed in anechoic chambers operate effectively in a wide
range of wavelengths shorter than a certain ultimate wavelength which is governed
by the thickness of the material as well as the average value of the dielectric
permittivity. The reflection fram their surface depends little on the incidence
angles.
Radio absorbing materials are produced by the American company of "Emerson and
Camin" in the form of sheets of flexible or solid plastic foam. They are fastened
to the surfaces being camouflaged with glue or special plastic clamps. The mater-
ials are sometimes made in the form of bricks from which walls are built up. The
solid materials for floor decking are covered on the top with sheets of fabric
glass l~inate. This same campany also produces, becsides the sheets of absorb-
ing material, f inished panels faced with a coating. The dimensions of the panels
are 1,800 x 1,800 :am2 and 2,700 x 1,200 ~2.
Returns from the support stands on which the model is secured can also be reduced
by means of radio absorbent materials. These stands or supports frequently fabri-
cated from plastic foam. To reduce the returns from the supports, they are given
the shape of a cone or inclined cqlinder, while the surface is made with a toothed
shape .
The background radiation can likewise be reduced by shaping the transmitter
antenna directional pattern so that its minimum is directed towards the most
dangerous re-reflectors. Because of the fact that the power appearing at the
receiver input changes in accordance with a 1/R4 law, it is advantageous to choose
the spacing between the antenna and the model less than the distance to the inter-
fering objects.
-26-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
It makPS sense to select the dimensions of anechoic rooms great enough so that the
target can be set up as far as possible from the back wall, which must additionally
be covered with the best of the absorbing materials available to the experimenter.
Fer example, anechoic chambers having a length of 40 to 50 m have been built in
the U.S.
~f the dimensions of the model are so great that the distance to it should exceed
30 to 40 m, special open test sites are employed. The effective radar cross-
sections of targets can be studied at such test sites just as if the targets were
located in free space and at a separation boundary. In the latter case, the trans-
ceiving antenna and the target are placed at the surf ace of the earth at such a
height that with the interaction of the forward and return beams from the earth, a
maximimm is obtained in the interference picture. Such a test facility will be
- described below in more detail.
3. Instrumentation Systems for the Study of Effective Back-Scatter Cross-Sections
Using Models ~
The major difficulties which are encountered in the study of effective radar cross-
sections are related to the segregation of the return signal from the transmitter
signal and the suppression of undesirable returns from surrounding objects. At the
' present time, the following main types of ineasurement systems are employed:
--CW systems;
--Pulsed; ~
i
~ --Systems utilizing the doppler effect.
~
-i A C',J System. This is the l~ast expensive system. It is usually employed for
; working with small models, where the measurements are ma3e in anechoic chambers at
~ distances of up 15 m from the model.
I ~
i
I A block diagram of a CW .instrumentation system is shown in Figure 2.1. The system
~onsists of a transmitter and receiver (1, 7), connected to the corresponding arms
i~ of a twin T-waveguide bridge, hybrid tee 5. Tuning units 4 and matched load 3
j are connected to one of the arms of the bridge, while foreign antenna 9 is con-
~ nected to the other which serves simultaneously f or transmission and reception.
When using such a bridge, one must consider the fact that half of the received
"and transmitted" power is fed to the receiver, while half is lost in the load.
The wavegui.de tee should be made with strictly symmetrical arms. Only in this case
will there be complete decoupling between the trans~itter and receiver, while the
received return is split equally between the matched load and the receiver. In
practice, the load i:;intentionally slightly mismatched so that part of the signal
is reflected from it into the arm of the tee to which the receiver is connected.
This signal, the amplitude and phase of which is adjusted by means of the tuning
units, is used to compensate for parasitic background returns. The ratio of the
energy remaining following compensation in the arm of the tee, to which the
receiver is connected, to the energy in the transmitter arm is called the degree
of system decoupling. The requisite degree of decoupling increases with a decrease
-27-
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
in the effective radar cross-section of the object being studied, with an increase
in the requisite precision of the measurements and range to the target. To reduce
~ 2
!0
3 4 S - 9 Q
6 7 A
(11)
NN~opMOyna 06 ytAe
Figure 2.1. Block diagram of a CW system for the measure-
- ment of effective back-scatter cross-sections.
" Key: 1. Regulated oscillator;
2. Decoupler;
3. Matched load;
4, RF tuning units;
5. Iiqbrid T-joint;
6. Autorpcorder;
7. Receiver;
8. Mixer;
9. Transceiving horn antenna;
~ 10. Support f or the model;
- 11. Information on the angle.
temperature influences on the level of decoupling, the waveguide T-joint and the
antenna are fabricated from Invar, while the tuninF; rods in the arm of the matched
load are made of quart~.
Extremely stringent requirements are placed on the stabilitq of the oscillator,
since a frequency deniation in it leads to the unbalancing of the bridge, a degra- ~
dation of t.he decoupling and consequently, to a reduction in the receiver sensit-
ivity. If is figured that in a system operating in the 10 cm band, the requisite
degree~ of stability should amount to 10'S for a isolation level of 85 dB and 5.8 �
� 10 for an isolation of 100 dB. Modern industrial samples of microwave oscilla-
tors provide the stability needed to maintain the requisite compensation level dur-
ing the entire measurement.time and can be used as transmitters and beat frequency
oscillators in superheterodyne receiving systems.
The follawing procedure is used for mea~urements made with such systems.
At the start of the measurements, the model is taken off of the support. The con-
trols of the tuning unit are set in a position such that no signal is detected in
the receiver arm. This means that the fields produced by returns from the supports
and background clutter have been cancelled out. After the model is mounted in place,
an uncompensated signal appears in the receiving arm of the waveguide T-joint from
the target, which is registered by the recorder. The model can be rotated in this
case 360� in azimuth or its positioned varied in the vertical plane. Then a
_ 28 .
FOR OFFiC~dL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
reference standard for which the effective radar cross-section is known is substi-
tuted for the model (sphere, cylinder, corner reflector) and the uncompensated sig-
nal from the selected reference standard is recorded.
By comparing the returns from the model being studied with the return from the
reference standard, the effective radar cross-section of the model is determined
directly. To obtain satisfactory precision with such measurements, it is necessary
that the effective radar cross-section of the rEference standard be of the same
order of magnitude as the effective radar cross-section of the model b eing measured.
The calibration of the equipment will be correct only in the case where the refer-
ence standard and the model are irradiated by a plane wave. If the irradiating
wavE is other than plane, i.e, its phase front is distorted, then the reflected
field will depend on the nature and magnitude of these distortions. In order to
check the correctness of the obtained return patterns from complex models, it is
necessary to make measurements of the field reflected from a flat plate, the pat-
tern of which is well known [lOJ.
If the transmitted wave is plane, then the angular width of the main lobe of the
secondary emission pattern of a plate of width a will be defined by the equation
9= x/a. The sidelobes will be twice ~s narrow as the main lobe. The level of
the first sidelobe should be 4.7 times less than the main one; the leveJ. of the
next one should be 7.8 times less, etc.
A check of the ratio of the levels is simultaneously a check of the linearity of
the entire receiving equipment channel. The measurement of the patterns of plates
with different widths a and their comparison with the calculated ones makes it
possible to determine at which dimensions�~tl~e pattern begins to be distorted s~
much that the irradiating field cannot be considered plane any longer [10].
' One of the variants of CW measurement systems is a frequenez~ modttZated CW system.
The operational principle of such a system consist~ in the fo~lowing.
A signal at a frequency of f~, which is transmitted at a point in time to and re-
flected by the scattering target (the model) at�a ran$e of R, is returned to the
receiver after T= 2R/c sec. Let the frequency of the transmitted signal change
_ at a rate of df/dt Hz/sec, and then the freque~zcy of the received signal will b e:
2R
f =fa-~- c dr'
If a small portion of the energy at a frequency of f~ is used as the heterodyne
- frequency and it is mixed with the received sigr.ial, then we obtain the difference
frequency: � 2R Rf
~r,=f -fe= ~ et' .
The signals reflected from objects located at ranges other than R yield other
values of fp. Interference from these signals can be avoided by means of tuned
amplifiers and filters with a high degree of selectivitq. The value of the eff ec-
tive radar target cross-section will be proportional to the amplitude of the re-
ceived signal.
-29-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFIC[AL USE ONLY
p ~ 4 5
1
6 7 9
g fl ?Z
~~J .
f0 1J
~v
Figure 2.2. Block diagram of a pulsed system for
effective radar cross-section measurements.
Key: 1. Pulse generator and time sweep;
2. Trigger pulse amplifier;
3. Modulator; .
4. Magnetron;
5. Transmitting ant enna;
6. Rece3ver and AFC system;
7. Waveguide attenuator;
8. Receiving antenna;
9:. Gated amplifier;
10. Oscilloscope;
11. Servo-amplfier;
12. Servamotor for the autorecorder pen and waveguide attenu-
~ ator drive;
13. Autorecorder;
14. Information so urce for the angle of rotation of the
model suppoxt.
A puZsed system takes the form of a simpl if ied radar adapted for operation with
models set up at comparatively short ranges (Figure 2.2).
The pulse technique makes it possible to obtain a high transmission pawer and
provides the capab ility of tuning out int erfering signals by means of using
speeial gating circuits. Pulses~of from 0.1 to 1.0 microseconds are used in the
equipment at repetition rates of from 500 Hz to 25 KHz. The intermediate frequen-
cies of the superheterodyne receiver run f ram 30 to 60 MHz with a bandwidth of up
to 10 M~iz. For the indicated pulse widths, no antenna switchers are used, but
separate antennas are used for transmission and reception. This is due to the
fact that the comparatively long switching and reset time of antenna switches
(gas dischargers) impedes normal operation with one antenna in the case of small
ranges (up to SO m) from the model being s tudied. Thelimitations related to the
selection of the minimimm range are practi cally eliminated, if nanosecond and sub-
nanosecond pulse widths are used in the equipment. Pulse systems with pulse widths
of one nanosecond and shorCer exist, something which makes it possible to obtain a
resolution of 15 cm and less. It is natural that such narrow pulses require a
very wide intermediate frequency bandwidth.
- 30 -
_ FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
DoppZer Measurement Sz~stans. The measurement principle in such systems consists in
- the following.
The ref~ecting object is moved relative to the observer at a def inite velocity
vr by means of a mechanical system. The moving object is irradiated with an elec-
tramagnetic field (with a wavelength a). The signal reflected fram it will have
a frequency which now differs from the frequency f by the amount ~f (the doppler
frequency):
~f = 2vr/~
The ~f frequency is segregated in the receiving equipment by means of comparing
the reflected signal frequency with the transmitter signal frequency. The ampli-
tude of the ~f frequency signal will be proportional to the effective radar cross-
section of the movin~ object. A block-diagram of one of the variants of such a
measurement system is shown in Figure 2.3.
Figure 2.3. A measurement installation using
rotation of the model and refer-
+ 6 ence standard, based on the util-
11
ization of the doppler effect.
~J Key: l. CW oscillator; 2. Waveguide tee-
joint; 3. Antenna; 4. Model;
~ S. Rotating angle mounting bracket;
j 3 4` 6. Reference standard; 7,8. The
~ s equipment wh ich receives and
~ i' records the signal reflected from
y_Y__~,' 6~ the model and the reference standard;
9. Switch; 10. Mixer; 11. Load;
~ 12. Stands for f astening the model
L_�J and the reference standard;
_ 13. Rotational drive with the switch.
The object being studied is mounted on a rotating angle bracket and irradiated by
a horn antenna. A reference standard reflector mounted in the place of the model
- at the same radial distance from the center of rotation is used to calibrate the
return level. The position of the transmitting antenna is chosen so that only one
object is irradiated. Thus, during the rotation of the mounting bracket, the model
and the reference standard alternately fall in the irradiating field. The return
from the rotating body is fed to the receiving arm of a waveguide tee-joint and is
mixed there with the referenee signal from the oscillator. As a result of such
mixing, a difference frequency ~f is segregated, which is then amplified and fed to
the recorder. If the objects are lucated at a distance r from the center of
- _ _ _ - - - - 31
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
rotation and their rotational rate is q r.p.m., then the maximum value of the
doppler frequency amounts to:
df = nrq/15a
There is a switch for the model and reference standard recording channel on the
rotating shaft, something which makes it possible to record both channels under
identical conditions and then, by means of comparing them, calculate the effective
radar cross-section of the target being studied. A mechanical system is provided
in the equipment, which makes it possible to slowly rotate an object about its own
axis si.multaneously with the rapid oscillation of the object, something which in
turn makes it possible to record its polar reflection pattern.
We shall consider open test site equipment for effective cross-section measurements
using the example of the American RAT SCAT facility [28].
- 4. The RAT SCAT Facility for the.Measurement of the Effective Radar Cross-Sections
of Various Objects
The RAT SCAT (RAdar Target SCATter Site) test facility is the largest open air
complex in the U.S. for static measurements of the effective radar cross-section
of obj~cts.weighing up to 3.6 tons. It makes it possible to perform effective
radar cross-section measurements in a frequency range of fram 0.1 to 12 GHz for a
specif ied transmitter and.receiver signal polarization.
0
- i ~i
i Figure 2.4. Plan of the RAT SCAT test facility.
I (
~ r I Key: 1. Rotating test stands;
~'o; ! 2. Roads for bistatic measurements;
I 2 ~ 3. Building where the radar
J equipment is housed.
J60M 150~+ i .
n
L._.
l250~.
Measurements can b e made at the test facility 75 percent of the days out of a year.
The size of the test site is 1,830 x 1,220 m. The overall layout of the test site
is shown in Figure 2.4. The objects being measured are positioned close to the
ground surface on plastic foam supports with small effective back-scatter cross-
sections. Calculations and experiments show that even with slight changes in the
soil characteristics, which can be due to climatic conditions, a directional pat-
tern can be obtained for any polarization similar to that shown in Figure 2.5 in
a frequency range of 0.5 to 12 GHz. In this case, the mounting height of the
-32-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
antenna and the object as well as the range to the object remain within limits
- acceptable for practic.e. In order to be able to simultaneously measure the
effective cross-sections of serveral objects, three rotating stands are positioned
at distances of 150, 360 and 750 m from the radar building (Figure 2.4). Three
devices for raising the antennas (to a height of up to 12 m) are set up around the
periphery of the building, each of which supports transmitting and receiving
- antennas.
Simultaneously with monostatic measurements, bistatic measurements (two position)
~ can be made at transmitter--target--receiver ~eparation angles ~ of up to 120�.
- For this, there are three tracks on the test sites along with the device for
raising the antenna moves as well as a bus with the equipment.
The main equipment c anplex consists of transceiver systems, each of which operates
in one of seven frequency subbands, something which makes it possible to continu-
ously cover a range of from 0.1 to 12 GHz; seven additional receiver systems are
housed in the bus with the equipment and are used for the two-position measurements.
There are also six sets of circular antennas with diameters of from 0.6 to 9 m and
a set of polarizing units for each frequency band.
~
~ Z~ Figure 2.5. Idealized antenna directional
R~ pattern of the RAT SCAT facility.
~ 4 h~
rn,, Key: 1. Equal field intensity curve;
-3 R ~ 2. Equal phase curve;
3. Mir.ror image of the antenna.
Z 3 ~ Figure 2.6. Block diagram of the receiver of
- s the RAT SCAT facility.
6
' e M 9 Key: 1. Signal from the RF mixer;
2. Intermediate frequency amplifier
. (60 MHz) ;
~a ~Z 3. Gating circuit;
4. Error detector;
- ~J 5. Amplifier;
6. Timing circuit;
7. Reference attenuator;
8. Digital and analog deviees; 9. Drive; 10. Gating circuit; 11. 9ignal to
the recording equipment; 12. Timing circuit; 13. Reference signal generator.
* * *
The minimal peak power ofeach of the seven transmitters is 1 KW. The oscillators
- for the transmitters in the five upper subbands are designed around TWT's; triode
oscillators are used in the two lower subbands. The pulse width can be caried in
all severn subbands from 0.1 to 1 microsecond, while the repetition rate can vary
from S00 to 5,000 Hz.
-33-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
Superheterodyne receivers with autamatic gain control at an intermediate frequency,
- which amounts to 60 MHz, are used in the system. The bandwidth is 2 to 10 MHz.
The primary amplifier channel is coupled to the reference signal oscillator, to
obtain a linear output signal proportional to ':'~e value of the effective radar
target cross-section in decibels (Figure 2.6). A range gating circuit passes the
signal reflected fram the object; the circuit passes the reference signal after
approximately half of the interval between pulses. These two signals are compared
with respect to amplitude, and the difference signal is used as an error voltage in
a tracking circuit which controls the angle of rotation of the shaft of a precision
reference attenuator. The tracking sqstem generates~the error signal; the level of
the signal proportional to the effective radar cross-section in decibels is deter-
mined from the position of the reference attenuator shaft. This is accomplished
by means of analog and digital coding devices. Such a method provides for auto-
matic compensation for the nonlinearity of the intermediate frequency amplifiers.
The control consoles and recording equipment make it possible for the operator to
monitor and control all of the ti.ming circuits of the radar, the position and
- angular velor,ity of the rotating devices, the position of the reference standard
reflector as well as the choice of antenna polarization and reference pulse ampli-
tude.
The radar return is recorded in polar and cartesian coordinates on two autorecorders.
~ digital recording is also made at the same time on punched tape, which makes pos-
sible to record data incaming via th e azimuth channel in intervals of 0.1, 0.2,
0.4, 1, 2 and 4 degrees.
-34-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFF[CIAL USE ONLY

~ CHAPTER THREE. REDUCING THE EFFECTIVE RADAR CROSS�-SECTIONS OF OBJECTS BY USIN~
POORLY REFLECTING SHAPES AND RADIO ABSORBANT MATERIALS
1. The Use of Poorly Reflecting Shapes
Having obtained exhaustive data on the effective radar cross-section of the
_ object being protected, one can set about solving one of the major problems of
antiradar camouf lage: reducing the radar visibility of the object by means of
reducing its effective back-scatter cross-section.
Reductions in the effective radar cross-sections of various targets can be achieved
in two ways:
--By imparting a poorly reflecting shape to the object being protected;
--By using radio absorbent materials.
It is obvious that the maximum masking eff ect can be achieved with an efficient
combination of both methods.
The gen~ral principle for the use of poorly reflecting shapes is the unparting of
such a shape to the object that the maximum of the reflected electromagnetic energy
is deflected to the side away from the direction to the radar receiver. This
phenomenon can also be supplemented with chaotic scattering in various directions.
The most characteristic poorly reflecting shape which deflects the maximum of the
reflected energy in the direction of the reaeiver is an inclined platte or pyramid.
A characteristic feature of a cone is the deflection of the maximum of the second-
ary emission pattern from the direction to the radar and the scattering of the
reflected energy in various directions.
Comparative values of the effective ratiar cross-sectians of simple reflectors are
shown in Figure 3.1, for which the geometric areas S of the surf aces being
- irradiated are equal (1 m2). Objects, in the structural design of which flat or
" cylindrical surfaces normal to the direction of irradiation, as well as corner
reflectors, predominate have the greatest value of Qt, where the geometric dimen-
sions are the same. These ~bjects are easily observed by radars at long ranges.
Consequently, a basic condition for the use of poorly reflecting shapes is the
priority replacement of structures having such surfaces with conical, pyramidal
or flat surfaces with a particular angle of inclination with respect to the hori-
zontal.
First of all, it is necessary to eliminate from the structure of the object being
- protected those corner reflectors which have large values of Qt with small boundary
dimensions, where the signals from such reflectors are stable on the display of a
radar set. Dihedral and trihedral corner reflectors can be formed by the combina-
tion of the side of a ship and a smooth sea surface as well as by the combination
of deck and superstructure surfaces. The surfaces of buildings, in conjunction
with smooth pavements and bridges, form powerful corner reflectors with large
surface dimensions.
-35-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
If it is impossible to employ poorly reflecting shapes on an object because of
structural design requirements, antiradar shields are used. A shield takes the
form of a current conducting sheet, which is installed with an inclination to the
vertical wall of the object being camouflaged (buildings, docks, the walls of
mooring berths, etc.). A drawing depicting the protection of a submaririe in its
. berth with an antiradar shield is shown in Figure 3.2. As has been reported in
the foreign press, although such shields do not completely camouflage the protected
objects, they nonetheless considerably reduce the power cf the reflected signals,
something which in turn has an impact on the clarity of the image on the display
screen.
Same foreign specialists believe that such effects (although to a lesser extent)
can be achieved if the vertical surfaces of the object being protected are not
- made smooth, but with a relief (corrugated). Such a ceramic plate is shown in
Figure 3.3, which is proposed in the FRG for use as camouflage for residential
buildings and industrial enterprises. Components which absorb radio waves can be
introduced into the lower portion of the plate.
Moreover, West German specialists have proposed that grooves, channels and cup-
shaped projections or depressions be made in the exterior surfaces of buildings to
reduce the reflected radar signal power for the purposes of camouflaging industrial
and residential buildings. To mask vertical planes and straight lines which form
the outline of ~ building, it is recou~ended that the f lat surfaces be broken up
with grooves, which run in arbitrary directions; the rectangular outlines of
- fondations, doors, windows and entrances are to be provided with projections and
~ cup-shaped add-ons, which distort the shape of these objects. Panels can be
installe~l at an angle of 45� to the wall of a building above windows and doors
and grooves, channels ~nd pro~ections can be made on the outside of the panels [7).
+ Figure 3.1. Comparative values of the effective radar
90' 90~ cross-sections of reflectors of various
\ r geometrical shapes .
s.r,.
' ~ 6�iZS~M:
90'
I 5=1N1
e�rzsoM' Considerable work is underway in the
( U.S. to reduce the reflectivity of
the warheads of ballistic missiles by
means of imparting a pocrly reflecting
~ S�rr' geometric shape to them. It is reported ~
e-110?+' in published materials that the effec-
tivp radar cross-section of a warhead,
S,~�r usually asstmmed to be 0.2 m2, can be
6.o~J�t reduced by a factor of almost 1,000. As
_ ~ r- is well known, the tl:eoretically ideal
poorly reflecting shape is an infinite
cone, viewed from the vertex. The nose-
S"~~t cones of missiles being developed in
6�~Nt
-.E-
,.S
-36-
FOR OFFICiAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFiCIAL USE ONLY
the U.S. at the present time have a minimal effective radar cross-section because
the electrical characteristics of an infinite cone are repvoduced in them with
the greatest possible precision. This is done by means of imparting a cone shape
to the missile nose cone with an ablation shield, in order to reduce back-scatter-
ing to a minimum, as well as by making appropriate changes in the ou tlines of the
base of the nase cone to reduce diffraction. Sharpeaing the nose cone of a warhead
not only reduces its effective radar cross-section, but also attenua.tes the shock
wave and leads to less surface heating, something which considerably reduces
ionization. In this case, a higher penetration velocity through th e atmospheric
lavers is achieved and sharp aerodynamic braking of the nose cone begins at consid-
erably lower altitudes. The problems of the enemy in tracking the missile warhead
and intercepting it are thereby complicated a great deal.
1 Figure 3.2. Antiradar shield on a submarine.
Key : 1, 3 . Shield;
_J = 2. Conning tower;
_ - 4 . Hull .
4i _
i Figure 3.3. Ceramic pla.te which scatters
I ~ the radio wave energy impin~ing
, I!' I I i 1 on it.
-I ~
' ~IIII~~~ ,~~IIIII ~
'
~ .
;
Despite the f act that a pointed shape f or missile nosecones is theoretically the
~ most advantageous, it proves necessary in practice to round off the sharp points
! of the cone somewhat for the purpose of reducing its burn-up.
' A shape close to a hemisphere, but having a specially designed doub le curvature
to reduce the energy flux reflected in th e direction of Irradiation can be the
- optimal one for the base of the conical surface of a missile nose cone. To reduce
diffraction and b ack-scatteiing, it is proposed that radio absorbant coatings be
used on the back side of a missile warhead in areas having sharp edges and projec-
t ions .
The back-scattering from a missile nose cone is a function of frequency. The
energy radiated b ack in the direction of th e irradiating source due to diffraction
reaches a maximum when the wavelength approaches the dimensions of the warhead.
The energy of the radio waves scattered from the sharp point of the cone and from
the sharp edges of the missile warhead increase in direct proportion to wavelength:
- - 37 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
the greater the wavelength, the greater the back-scattered energy is and the smaller
the vertex angle of the cone, the smaller the back-scattering is.
e ~ . .
1 1 3 4 3 6'
Figure 3.4. Nosecones of U.S, b?llistic missiles.
Key: 1. Mark 2(Atlas, Thor missiles);
2. Mark 3 (Atlas missile);
3. Mark 5(Titan 1 missile);
~ 4..Mark 6 (Minuteman missile);
~ 5. Mark 6(Titan 2 missile);
6. Mark 7 (Skybull missile);�
7. Mark 11, 11A (Minuteman missile).
The nosecones of ballistic missiles in U.S. armaments are shown in Figure 3.4.
- 2. General Information on Radio Absorbent Materials
In the middle of the Second World War, the English employed aircraft radar to
search for submarines, something which sharply increased losses in the German
fleet. To retain the major tactical advantage of the submarine - the fact that it
- is hidden, the Germans set abouz the design of radio absorbing materials. The
conning towers and extendib le equipment of submarines were covered with such
materials. The coatings were supposed to absorb the electromagnetic energy incom-
ing from the radar transm itter.and reduce the submarine detection range by an
aircraft radar.
In the opinion of foreign specialists, radio absorbing materials are a promising
means of antiradar camouflage at the present time too for military and industrial
objects. They are being developed primarily to shield aircraft fnr the purpose of
facilitating the penetration of aircraft and missiles to an air defense line.
The operational principle of such materials consists in the fact that the absorbed
radar energy is converted to other kinds of energy in the material itself. In this
case, the phenomena of electromagnetic wave absorption, scattering and interference
occur. In the case of electromagnetic energy absorption, the incident wave field
is attenuated because of the conversion of the f ield energy to heat.
- 38 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007102/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
- Such a process is primarily explained by the presence of dielectric and magnetic
losses in the absorbing camouflage material. The scattering process is the con-
version of the electromagnetic energy flux which propagates in a certain directi0n
in the material to fluxes in various directians. The radio wave interf erence phe-
nomenon (on analogy with optical interference) is responsible for the reflectivity
of an absorbing material in the direction of greatest secondary emission from its
surface.
In terms of structural design, absorbing materials can be broken down into t~ao
main types:
l. Radio absorbant coatings - materials which are appl.ied to the surface (as a
rule, metal surface) of the object being protected.
2. Radio absorbant construction mat~rials: such materials, which are used for the
_ construction of military or industrial facilities, comb ine, along with good strength
characteristics, the property of absorbing radio waves transmitted by enemy search
radars.
The following requirements are placed both on these and other material:
--Minimal radio wave ref lection from the surface b eing protected;
--Maximum electromagnetic wave absorption;
--A wide frequency range of absorbed energy;
'I~
-i -High strength characteristics;
I --Minimum size and weight;
I
~ --Capable of operating in a wide range of positive and negative temperatures.
i
I Radio absorbant materials can be broken doen into two main types, according to
~i
I the operational principle: narrow band types, which are interference materials and
broadband types, absorb ing materials. In narrow band interference coatings, the
I!~ secondary radio emission is suppressed because of the interference of the radio
waves reflected from the exterior surface of the coating and the surface of the
object being camouflaged. In broadband absorBing materials, because of their
definite structure, there are no reflections from the external surface of the
material and almost all of tfi e electromagnetic wave energy entering the camouflage
coating is gradually attenuated and converteC to heat by virtue of the induction
of scattered currents and magnetic hysteresis or high frequency dielectric lossps.
Depending on the electrical and magnetic properties, radio absorbing materials can
_ be broken down into dielectric an~ magnetic-dielectric types.
-39-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
3. Some Questions of Theory
An absorbing naterial will correspond to its designation in the case where thereneg
no electromagnetic wave reflection from the external surface while the energy p
trating into such a materlal is completely absorb ed in it. Meeating these condi-
tions is achieved through the appropriate choice of the electrical properties of
the material, primarily the complex dielectric percnittivity and the complex magnetic
permeab ility:
e=e'-je",
~~=~i -j~~�
The imaginary camponents of the permeability and permittivity are due to losses in
the material. We shall consider the conditions for the abseence of electromagnetic
energy reflection ~rom the absorbing material. Let this material with electrical
parameters of e and u have the form of an infinite plane, where a radio wave
arrives from the external space (elul) normal to the plane (Figure 3.5).
The field of such a wave at the surface of the absorbing material and the field
inside the material will be described by Maxwell's equations (5, 9]:
(3.1)
~ ~kZ L S@-Ikz
E: _ e T )
z~0,
If - E~. ~e~k: - se lk:~
~ ~ 12a
~~a
i ~
E" e~e ~ a 0.4, where a is the
radius of the sphere), just as is to be expected, back-scattering decreases when
a coating is applied.
Back-scattering by cones in the Rayleigh region when a coating is applied increases
considerably (by 20 dB), and the back-scattering level begins to fall off in step
_ with an increase in the diameter of the base of the cone, i.e., as the region of
*-esonance scattering is approached.
4. Varrow Band Interference Coatings
The simplest interference coating takes the �onn of a resonant absorber, consisting
of a homogeneous dielectric layer applied to rhe metal surface being protected.
The thick^ess of the dielec~~ric layer d, its dielectric constant e and the tangent
of the dielectric loss angle, tand, are chosen so that the ref lection factor for
the incidence electromagnetic waves is equal to zero.
Camouflage interference coatings are manuf actured abroad from various plastics or
rubber, filled with graphite powder or carbonyl iron. Merits of such coatings
are their considerable mechanical strength, flexibility, comparatively small
thickness and low weight. A major drawback consists in the fact that absorption
takes place in a narrow band of frequencies. This is related to the basic condi-
tic~n for obt~.ining a nonreflective interference coating: its thickness is a func-
tion af the transmitter wavelength as well as the dielectric permittivity e and
the magnetic permeability y of the material itself, i.e.:
d= ~
~ y~� .
- -43-
,
FOR OFFICiAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR O~FICIAL USE ONLY
.
In order to meet this condition, it is necessary to precisely choose the quantities,
_ e, u and the thickness of the coating. The coatings can be rather thin for short
wavelengths with large dielectric and magnetic losses in the material. Interferen~e
materials work well only in the case of normal incidence of the radio waves on
their surface. At other incidence angles, the reflection factor of the coating
increases sharply. .
TABLE 3.1
Characteristics of Narrow Band Camouflage Coatings
Brand of Thick- Wavelength Band- Weight, Reflector
Material ness, Range, cm width, kg/m2
%
mm ~
~1 2 3-3.4 10 7 Copper
~{3 Z - 10 9 Fabric
_ MS1 4 - 24 17 Copper
MS3 4 9.1-10.5 24 17 Fabric
Pore� y
2
_ Pra~,
Figure 3.8. The power reflected from the MX1
~ coating as a function of w~ave-
� length for the case of normal
o incidence.
3,0 .?,1 3,7 3,3 ~,,cM ~
P~e,%
~ref Figure 3.9. The pawer refle�Eed from the MS1
Z coating as a~unction of the wave-
length for the case of normal
~ incidence.
0
7 9 9 /0 Jl 11ycM CA
The type MX and MS radio absorbent coatings developed by the English firm
"Plessey Company", can serve as the most characteristic example of narraw band
interference materials (Table 3.1). The basis of the coatings is rubber which
is mixed with carbonyl iron. The back side of the materials is coated with
copper sheet or flexible brass fabric. In the latter case, the coating can bend
to fit the shape of the camouflaged ob~ect.
The bandwidth of MS material is considerably wider than that of MX because of the
large content of magnetic material, and consequently, the large values of u and
-44-
FOR OFF[CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
- the characteristic impedance. These materials take up little space, and if their
back side is firmly fastened to tfi e solid surface of the camouflaged object, they
are good conductors of heat, and can absorb and dissipate approximately one watt/
/cm~. During a short-term exposure of such materials to a field with a power of
approximately 200 KW on a surface of a few tens of centimeters, no changes were
observed in their properties.
Curves showing the power of the reflected signals as a function of the wavelength
and the angle of incidence for the MS1 and MX1 materials are plotted in Figures
3.8 - 3.10. They all have a narrow absorption band, and moreover, the power of
the returns rises rapidlq with an increase in the angle of incidence.
Po~o.'^ ~ Figure 3.10. The power reflected from
the MS1 coating as a
~x~o � function of the angle of
- incidence ~ at a wave-
~ Z length of 3.2 cm.
2
Key: 1. Horizontal polarization;
0 2, Vertical polarization.
l0 ZO zo 4p y. tvad degrees
- Type I~C and MS coatings with a small thickness and low weight have a comparatively
high mechanical strength, something which makes it possible to use them for the
antiradar camouflage of small mobile objects: motor vehicles, tanks, small ships,
buoys, the helmets and weapdns of night patr.ol.s,: etc. [21, 30, 39].
~ T'he RS radio absorbing interference coating, designed for operation in the three
' centimeter band, was developed in the U~S. The coating is manufactured in the
~ form of f lexible plastic sheets 1.75 mm thick, with which metal objects of any
i shape can easily be covered. This covering provides for a reduction in the re-
' flected power by a factor of 100 (as compared to reflection fram a metal surface)
at a wavelength of 3.2 cm. The material is distinguished by good strength charac-
' teristics, it can operate both at high (up to 205 �C) and below freezing tempera-
' tures, as well as in conditions c~f solar radiation, wind and rain. A square meter
~ of such a covering weighs about 5 kg.
It should be noted that the production process for the fabrication of thin sheet
and film interference coatings, which have good radio engineering and mechanical
properti~s, is extremely complex.
_ Here, for example, is how a radio absorbent material is fabricated for a resonant
frequency of 7.5 � 109 Hz. The technology was developed by the American firm of
"Dupont de Nemours Company". It is first of all necessary to fabricate the so-
called neoprene absorbing cement, the composition of which includes the following
components: 150 parts neoprene, 3 parts phenyl-~-naphthyl ~nine, 7.5 parts zinc
oxide, 6 parts calcined magnesium oxide, 0.75 parts stearic acid, 84 parts furnace
black and 494 parts xylol. At first, the phenyl-s-naphthylamine, magnesium oxide,
- -45-
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
zinc oxide, and furance black are mixed in a special mixer for three minutes at a
temperature of 43 �C. Then the temperature is lowered to 35 �C, neoprene is added
to the mixer and the temperature is again increased up to 88 �C for seven minutes.
The mixing is carried out at this temperature for five minutes. The resulting
_ camposition is placed in a rubber mill, where the zinc oxide is added to it at
room temperature. Such a mixture, which is prepared in a cold rubber mill, is
pla~eu in a paddle mixer and half of the xylol contents are added, after which the
intermixing continues for another 5.5 hours. The cement solution prepared in this
manner contains 33.? percent solid material by weight and is filtered through a
fabric filter to remove the insoluble clumps. Then a homogeneous compositioa is
prepared fram the f iltered mass, which is suitable for application to a flat surf-
ace with a conventional putty knife. For this, 171 parts by weight of neoprene
cement is mixed with 12.6 parts by weight of graphite and 42 parts toluene. Such
a solution is applied to the surface of glass plates (coated beforehand with a
polyvinylchloride film 0.025 mm thick) and dried for 30 minutes at room temperature.
Yet another coating layers are applied in the same way. The finished coating is
removed from the glass plate, kept at a temperature of 70 �C for 24 hours to
remove the solvent and is vulcanized at a temperature of 140 �C for an hour.
The vulcanized film 0.5 mm thick contains 11.9 percent (by volume) graphite and
22.7 percent (by volume) furnace black. Three such films are placed one on top
of the other and pressed. The finished film is firmly joined to the metal foil. �
It is reco~ended that graphite and acetylene b lack be used to absorb lawer fre-
quencies, and in this case, their content in the film is increased up to 25-50
percent (by volume).
Also of interest is the work underway abroad on the design of radio absorbent
materials which take the form of a system of dipoles oriented in a dielectric and
- arranged at a distance of a quarte~.r wavelength fsam the metal surface of the object
being camouf laged. It is believed that such 1 system will make it possible to
extend the bandwidth in which narrow band materia's operate. It has been deter-
mined that for each length of the dipole used in the absorbing system there exists
a lattice coastant for the grid formed by the dipoles such that the refl.ection
- factor is minimal.
Under actual modern combat conditions, a large ntunber of radars will be used
simultaneously which have various working wavelengths. In this case, narrow band
interference coatings will have little effectiveness. Broadband radio absorbant
materials are considered more promising. As a rule, they have considerable thick-
ness and wieght, but nonetheless can camouflage the objects they protect against
radar stations operating at different frequencies.
5. Broadband Radio Absorbent Coatings and Materials
- The development of broadband radio absorbent coatings, which were intended for
camouflagi~g submarines, started during the Second World War in Germany. The
coverings consisted of a number of layers, the conductivity of which incre~sed
with depth. The layers were separated bq a foam-like plastic with a dielectric
-46-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICiAL USE ONLY
permittivity close to unity. Absorption was good in a range of wavelengths from
4 to 13 cm. However, because of the great thickness and considerable weight, the
- covering samples which were developed did not find practical application.
Many industrial companies and scientific research organizations abroad are working
on such materials at the present time. It is believed that the use of absorbing
coatings on aircraft and missiles will make it possib le to significantly facilitate
their penetration of air defense zones of an enemy, saturated with radars operating
in a broad range of frequencies. The opinion has been put foreward that if even
the speed of a camouf laged oUject is reduced through of such materials, the then .
slow nuclear weapons vehicle which is poorly visible on a radar screen can prove
to be more dangerous than a fast vehicle which produces a strong return and is
detected by the radar at a great range. A merit of such materials is also the
fact that they do not have to cover the entire camouflaged object, but only the
"shining" areas of its surface which are determined during the process of studying
the effective radar cross-sections of various targets.
TABLE 3.2
Characteristics of Broadband Camouflage Coatings
Lower Maxi- Weight Cost per
Brand Limit of mtmm Thickness, per Square
the Wave- reflec- ~n Square ~ieter,
length ted Meter, Dollars
' Range , cm po~~er, % kg
AN-W-72 1.5 1.5 3.2 0.4 48.5
; ~,N-W-73 4,0 1 9.5 0.8 54
' AN-W-74 8.6 1 15.9 1.2 63
~ AN-W-75 12.5 1 25.4 2.0 72
AN-W-77 32.0 1 53.5 3.5 117
AN-W-79 66.0 1 114.3 8.0 140
~ ~
~ The American company "Emerson and
~ Camin" produces the AN-W series of radio
absorbent materials, which are recom-
mended for use on aircraft and objects
exposed to the open air (Table 3.2).
The compan~ advertises this material as
light, flexible and a sheet covering
which can assume the form of the object
being protected. The dimensions of a
sheet are 600 x 600 mm. The covering
parameters do not depend on the weather
and do not change at temperatures of
Figure 3.11. AF-11 radio absorbent from -55 to +150 �C. A neoprene fabric
material, the outer surface covered with nylon is applied to the
of which is corrugated. material, which is glued to any surface.
-47-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
The type RM "Echosorb" broadband radio absorbent material was also developed by
the same company to camouflage aircraft and space vehicles. It takes the form of
a flexible silicone foam capable of operating for a long time at high temperatures
(up to +260 �C). The pow~r reflection factor in a range of wavelengths of from
4 cm ans shorter does not exceed 2 percent. Changes in the polarization plane of
the incident energy or the angle of incidence have little effect on a change in
the reflection factor. The material is produced in the form of sheets 300 x 300 nm.
At a thickness of 9.5 affi, the weight of one square meter of the material is 2.98 kg.
~ variant of the RM "Echosorb" has been developed for a range of wavelengths of
8 cm and shorter. It weighs 6.85 kg/m2, while the thickness is 28.6 ~n [43).
The English firm of "Plessey Company" produces the AF series of broadband radio
absorbent materials, which are intended for camouflaging stationary objects or
objects which move at a slow velocity (Figure 3.11). These coverings are specif- ~
icallv reco~ended for use in camouf laging the superstructures of ships, buildings,
port f acilities, canals, etc. [7, 30].
The AF-10 material is fabricated from two layers of porous rubber, mixed with
carbon dust. The absorption increases gradually frnm the first layer to the
second. The ~overing layers have the following characteristics:
First Layer Second Layer
Characteristic impedance, ohms 225 190
Attenuation, dB/m:
At a frequency of 3,000 MHz 125 ' 210
At a frequency oL 10,000 Mliz 540 970
In the case of normal incidence of a b eam on the first layer, the power reflection
factor in a range of wavelengths of 3 to 10 cm is 6 percent. The corrugation of
the surface reduces it down to 1 percent in the 10 cm band and down to 0.2 percent
in the 3 cm band. Because of the relief surface, the reflection factor depend s
little on the angle of incidence.
The AF'-11 coating which is intended f or wavelengths of 5.7 cm and shorter has
finer absorber grains and less weight than the AF-10.
Po*o.�% Figure 3.12. The electromagnetic power re-
~ _ _ flected fron AF20 material as a
- function of wavelength for the
- case of normal incidence.
0
~ 3 5 7 o a.r.M
-48-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ON~,Y
. Po~o. x
Pref. Figure 3.13. The electromagnetic pawer re-
o,so flected from AF-20 material as a
function of the angle of inci-
~ 2 dence at a wavelength of 3 cm.
0,15
Key: 1. Horizontal polarization;
0 2. Vertical polar~zation.
~0 30degrees o�rpod
The lightest ?nd hardest covering is the AF-20 type. It consists of pressed grains
of polystyrene foam, surrounded by a tough carbon film. The front side is likewise
corrugated, just as the AF-11 material. The AF-20 materials can be used in open
air if their surface is protected by a layer of hydrophobic sil'_ceous paint. In
this case, atmospheric moisture can form individual drops, which do not increase
reflections, on the corrugated surface of the covering. The reflection fact~~r from
such a coating does not exceed one percent with respect to power in a wide range
of wavelengths (Figures 3.12, 3.13).
Ferrites have found widespread applications in recent years for the manufacture of
broadband radio absorbant materials. Coverings made of such materials are distin-
guished by light weight and small thickness. The American company of "Conductron"
manufactures material based on ferrites, intended for camouflaging the nose cones
of tiallistic missiles. It provides for the absorption of electramagnetic energy at
meter and decimeter wavelengths. Other broadband materials by the same f irm make
it possible to absorb radio emissions in a range from meter to centimeter wave-
lengths. Coatings of materials of this type have a thickness of 6.3 to 12.7 mm and
attenuate the reflected radiation by a factor of 20 to 1,000. One of these coat-
li in s 5 mm thick (a s uare meter of this coating weighs 4.9 kg) provides for a reflec-
g q
t3,on attenuation in a range of frequencies from 40 to 3,000 MHz down to 1 percent
II in the center of the band and down to 7 percent at the edges. The "Conductron"
~ company zs working on the design of a radio absorbent material to camouflage air-
' craft and missiles, which simultaneously has thermal shielding and radio absorbent
~ properties. It is thought that ablation heat shield coverings can be obtained
j with the introduction of plastics into the composition of the radio abeorbent cover-
~ ings developed by r.his company.
The radio absorbent fabric developed in the FRG is also of interest. It is proposed
that ground objects be camouflaged with panels of such fabric: aircraft on airf ields,
tanks, ordinance, missile installations, etc. The fabric has a layered grid struc-
ture, the cells of which are filled with graphite powder along with a binder. In
some layers of the fabric, the graphite pawder particles are arranged so that they
do not fill the cells completely .or uniformly, leaving air gaps. The camouf lage
panels consist of three or five layers, where the dimensions of the cells in the
layers are not the same [7].
Radio absorbent coverings for so-called anechoic chambers are produced abroad in
a wide assortment. Their structural design and use were treated in the previous
chapter. The most widespread tqp e of absorbing material for aneehoic chambers is
- 49 -
FOR OF'FICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
FR "Echosorb", which is used in the form of light foam blocks. It has a reflection
factor of one percent in a wavelength range of 0.6 to 12 cm with a thickness of S
cm (type FR-330) and in a range of wavelengths of up to 66 cm with a material
thickness oi 20.3 cm (type FR-350).
The "Echosorb " CHW material is especially recommended for operation at low fre-
quencies. It is produced in the form of solid or hollow pyramids, built into
_ blocks, as well as in the form of individual pyramids with a height of up to 1.8 m
(CHW-560) for frequencies below 50 MHz.
P.bsorbent antiradar structural materials occupy a special place among the means of
_ antiradar camouflage. West German specialists are intensively involved in their
development. For example, they have proposed using porous concrete in the form of
individual construction blocks for shielding against radar detection of buildings.
Because of the presence of air bubbles in porous concrete, the radio wave absorp-
tion in it considerably exceeds the absorption in conventional concrete. For more
intense absorption, it is recommended that graphite be mixed in the porous concrete.
A multilayer absorbing construction material design with different grain and pore
sizes in the layers has also been developed in the FRG (Figure 3.14). The outer
layer, which is irradiated by the electromagnetic energy first, amounts t~~ half of
the material thickness (having the fonn of plates or blocks) and contains the
largest grains. Underneath it is a layer in which the grains are considerably
smaller, and even lower is a layer of silica with graphite added. For practical
purposes, a three-layer absorbing plate is recommended, the outer layer of which
(11 cm) consists of grains with a diameter of 10 to 20 mm; the second layer (3 cm)
con~ains grains 1 to 3 mm in diameter. Underneath it is a laqer of fine pebbles
with graphite added, where the diameter of the pebbles is equal to approximately
0.7 nun. Radio waves wh ich penetrate into the second layer are partially refracted
and scattered back to the outer layer and partially absorbed in the pores of the
_ second layer.
Sometimes, two of these layers is
sufficient to achieve the requisite
- "�q~' ~ effect. The third fine-grained iayer
M'R R ~ ~ 3'
y~ i absorbs part of the electramagnetic
t�'S~
� ~'~i' energy and reflects part of it, and it
t, is attenuated when passing back through
- ~�rQO the layers with pores and hollow places
J ~ O~i`~ ~
'n of greater size.
. ~ f~ `a~~ tt
;
Work is intensively underway abroad
on the s~udy of the radio absorbing
~ properties of plasma for its utiliza-
- tion as a means of antiradar camouflage
f or missiles and space vehicles. It was
reported in the press that a radar
Figure 3,14. The structure of a three- emission absorption effect and a consid-
layer radio absorbent con- er.able decrease in the effective back-
struction material. scatter cross-section can be achieved
- with the radar probing of a metal sph ere
- SO -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
partially cavered aith a plasma layer. The plasma layer can be extremely thin as
compared to the radar wavelengtfi.
6. Measuring the Characteristics of itadio Absorbent Materials
The basic parameter to be measured, which must be known both during the process of
fabricating the material and in the final stage when testing the finished sample,
is the reflection factor of the coating s. The study o� the properties of radio-
absorbent mate:ials can be carried out using various techniques. The radio f re-
quency method has become the most widespread. In this case, the f ield intensities
E~ and ER of electromagnetic waves reflected from the absorbing material and from
a flat metal reflector respectively, where the latter has the dimensions of the
coating and is mounted in the same place, are compared:
s = EA/ER
A sample measurement set-up is shown in Figure 3.15. The transmitting and receiving
horns are positioned on supports, which can be moved in a vertical plane along a
semicircular arc. The sheet of absorbing material being tested is p laced in the cen-
- ter of the arc. The polarization is changed by rotating the horns about the axis.
~ 5.~~' I
j' ~ ~i~t,Fj~' ~ .
~ .
~.~a;f: ~ 1;~. .
Figure 3.15.
t,~ ~
a~~.~,� ^ , I,a;~ ;
I Set-up for measuring the reflection
factor of radio absorbent materials .
i r_
1~'� a~..
I
I ~ ~ '
t
I~
The t.ransmitting horn transmits the microwaves which are modulated with square wave
pulses, which pass through the graduated attenuator. The receiving horn is loaded
- into a semiconductor detector, which is coupled with a cable to an amplifier tuned
to the modulation frequency. ~
Having arranged the horns so as to obtain Che requisite angles of incidence and
polarization, the metal sheet is placed in the center of the arc. Then the attenua-
tor is set so a sufficiently fiigh reading is obtained at the output of the amplifier.
- 51 -
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
Then the metal sheet is replaced by the absorbing material being tested, and the
attenuation inserted with the attenuator is reduced until the previous reading is
obtained at the amplifier output. The difference in the two attenuator readings
yields the value of the power reflection factor:
s = 10 log(P1/P2) dB,
where P1 is the power level reflected by the material; P2 is the power level
reflected by the metal sheet.
The measurement frequency range is governed by the property of the horns and the
parameters of the RF generator. At lower frequencies, considerable errors appear
because of the increase in the dimensions of the horn and the surface areas of
the tested materials as compared to the spacing between them. In this case, the
reflection factor can be determined from the standing wave ratio (SWR). The
installation includes a horn, wiiich is matched to free space. The dimensions of
the horn are chosen so that the aperture angle of the exiting beam does not
exceed 12 degrees. The covering sheet is placed in front of the horn so as to
obtain the requisite irradiation angle.
The techniques have been deve?oped and the equipment designed at the pr~sent time
for the rapid determination of the dielectric constants and tangent of the dielc-
_ tric loss angle of radio absorbent materials. Hawever, it is thought that despite
the importance of these quantities, they are rather difficult to determine at a
directly specified point on a real ob3ect. It has been reported in the press that
it is obviously expedient to evaluate promising radio absorbent materials in the
future based on such variables as the capacitance and losses at audio f requencies,
- which are measured directlq on the object protected with the covering.
-52-
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-04850R000400070041-5
FOR OFF[C[AL USE ONLY
CHAPTER FOUR. THE MASRING PROPERTIES OF TERRAIN AND HYDROMETEORS
1. The Effective Back-Scatter Cross-Section~of Surf ace Distributed Targets
- The camouflage effect.of surrounding terrain objects consists in producing clutter
interference as a result of electromagnetic wave reflections from the surface of
the ground or sea, as well as from inhamogeneities in the atmosphere. The intens-
ity of these returns depends on the condition of the atmosphere, the nature of the
terrain around the radar station, the wavelength as well as the resolving power of
the radar. With a sufficiently high intensity, such clutter can significantly
reduce the operational effectiveness of the radar or even completely preclude the
possibility of radar operation.
- The specific effective back-scatter cross-section is taken as the measure of the
intensity of returns to characterize the masking reflections from distributed
objects (grass cover, plowed land, forest, shubbery, a sea surface, etc.). The
back-scatter level is usually taken equal to the effective back-scatter cross-
section of one square meter of distributed surface targets and is designated Qy.
We shall assume that a radar, locsted in an aircraft f lying at an altitude H, has
a pulse width T and an antenna directional pattern width at the half power level
of A. At each given point in time, the signal acting on the receiver input is the
result of the adding of the signals reflected from elementary reflectors arranged
in a random manner within the bounds of the reflecting area of the surface. The
geometric area of a distributed target section ("the resolving area"), as can be
- seen in Figure 4.1, will be equal to:
1 RO s ( 4 .1)
S,. n, - - , ec ~p,
_ where ~ is the angle of antenna beam inclination to the horizontal.
The value of the effective radar cross-section of a surface distributed target,
6~u, is defined as.the product:
Qu~~=Q~si~pa= 2 o,R~iSec~P� (4.2)
It can be seen from the derived expression that the effective back-scatter surface
area of such targets depends not only on the scattering properties of the surf ace,
governed by the quantity Qy, but on the oblique range, angle of wave incidence and
radar parameters. The signal from the surface target produces a rather intense
- ltmminescent l~lip on the radar screen, as w~~i as a"background", which interf eres
with the obseroation of. point targets located within the bounds of this surface
area" ships, tanks, industrial objects, etc. A target on the ground or water
surface can be detected by the operator only in the case where its signal is
-53-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLl(
segregated from the pips produced by the masking returns from the background
surrounding the target. Experimental data show that on a PPI display, one can
segregate a return from a reflecting surface on which a point target is located
from the reflecting areas adjacen~ to it which do not have point targets only when
the contrast factor is equal to:
K= ��~+a~ ~ ~~3-~-, 1.4~ (4.3)
a,,,, _ .
where Qu is th e effective radar c-ross-section of a point target and is the
effective radar cross-section of a surface target.
Pnc F
Radar l
Figure 4.1. The reflecting surface
- ~ " ~ area in the vertical (a)
\R'~ ~r and horizontal (b) when
~ scanning a grour.d or sea
, , , , . ~
' ~l 5~4 surf ace with a pulsed air-
craft radar.
Radar~~~
F er
6~
To i~prove the observability of point targets, it is necessary to reduce Qnu,
something which as can be seen from formula (4.2) can be accomplished by narrowing
the directional pattern in the horizontal plane 9 and reducing the pulse width T.
However, it must be noted that an improvement in the observability of a camouflaged
object through a reduction in T will not occur as rapidly as f ollows from expres-
sion (4.2), since when T is shortened, the bandwidth of the receiver must be
extended, b ecause of which its internal noise increases.
The effeccive radar cross-section of a surface target is also governed by the
quantity 6q, which in turn depends on the unevenness of the surface, the incident
angle of the electromagnetic energy, the wavelength, the polarization and the
dielectric permittivity of the irradiated surf~ce.
As is well known, irradiated surfaces in radar are broken down into smooth and
rough. ~ smooth surface is depicted on a display screen in the form of a dark
spot, since in this case, the incident beam is reflected away from it in accordance
with the laws of geametric optics and does not return to the receiver. In the
' case of a rough surface, a portion of the scattered energy returns back to the
antenna and produces a bright region on the screen. The transition from a mirror
to difuse reflection is related to the unevennesses of the irradiated surface.
-54-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-04850R000400070041-5
FOR OFFICIAL USE OR~~,Y
A surface can be considered smooth if the height of the uneven places on it, h,
with an angle of inclinatioa of tfie antenna beam to the horizontal, and a wave-
length a satisfies the expression:
~ ~ (4.4)
~ h~i6~int'
The majority of surface targets have an unevenness value which does not satisfy
expreesion (4.4). For such rough surfaces which produce a diff use reflection, the
specific effective radar cross-section is justified as a sinusoidal function of the
angle � :
a, =~vosin ~p~ ( 4 . 5)
where ap is the specific effective radar cross-section when n/2.
2. The Reflecting Properties of a Ground Surface
For centimeter band radars, the majority of dry land is a rough surface, primarily
because of vegetation. The reflecting surface of such objects consists of reflec-
tors which move little (hills, tree trunks, etc.) and reflectors which are in
chaotic motion with the action of the wind (grass, leaves and tree branches). The
' stronger the wind, the more intensive their motion. For this reason, reflections
from trees, shrubbery and natural.terrain features covered wi~h vegetation consist
, of a brightly expressed constant signal and a signal which f luctuates in amplitude
; and phase. Radar returns from a surface covered with vegetation ur_dergo seasonal
~ changes. Moreover, the nature of electramagnetic wave ref Tections from all sur-
faces depends strongly on their humidity and the presence or absence of snow cover.
I, The specific effective radar cross-sections of a ground surface covered with
'I forest is shown in Figure 4.2 as a function of the angle of antenna beam inclina-
i tidn to the horizontal, and summary graphs of:the functiaai vy = f(~) are
~ plotted in Figure 4.3 based on the results of averaging the data for various types
~ of terrain. As can be seen froYn this figure, the values of Qy for various terrains
~ occupy a region with comparatively clear-cut boundaries, so that one can judge the
overal character of the terrain from which an echo is received based on the value
! of ay. Thus, for example, the range of values of Qy for forested terrain at
various angles to the hori2ontal has an extent of no more than 5 dB. The specific
radar cross-section for desert terrain depends greatly on the nature of the soil
and the surf ace inhomogeneities, and averages 13 dB less than for forested regions.
Measurements made over three various regions of broken rocky desert yield very
lose results, where the course of the Qy = f(~) curve for a desert has almost the
same form as for forested terrain. The back-scattering by sandy desert (even, dry
sand) provPS to be the least of dry land. Back-scattering by the sea, as a rule,
is less than the scattering by dry land, and the values of Qy occupy a region 10 to
15 dB wide .
- 55 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
Electromagnetic energy scattering by built-up regions always exceeds the scattering
b~ forested terrain. The range of possible values of Qy for built-up regions of
the earth's surface is extremely wide (20 to 30 dB).
In antlradar camouflage, the nature of the background against which a paXticular
camouflaged object is located is of very great importance, since the background
frequently provides no small return, and some.times a greater return than the ob~ect
being scanned, which in this case, will not be detected.
When taking step directed towards the reductian of the effective radar cross-section
of any ground object, its size, shape and the material from which it is made must be
taken into account, as well as the reflectivity of individual background areas
surrounding the object being camouflaged.
A priority task in camouflaging ground objects of extensive area should be the
equalization of the radar return coefficients of the object being camouflaged and
the ambient background. This is achieved through the use of radio absnrb ent con-
~ struction materials and coverings in conjunction with poorly reflecting shapes and
shields. By reducing the effective radar cross-section of a camouflaged ob,ject and
somewhat boosting the returns from individual background areas close to the ob~ect,
the contrast boundaries between the target being camouf laged and the background are
erased. Individual structures (bridges, roads, dams, etc.) or group objects (con-
centrated troups or equipment, plants, warehouses, electric power stations, air-
f ields) are camouf laged in this way.
Thus, for example, it is recommended in one of the foreign references [38] that
concrete asphalt highways and landing strips at airfields be camouflaged taking
into account the surrounding background.
In the case of vertical scanning of a concrete strip, up to 60 percent of the
incident energy is ref lected in the direction af incidence. In the case of irradi-
stion at an angle of 45�, the amount of energy reflected in the direction of
arrival is zero. In intermediate cases, the return factor falls in a range between
zero and 60 percent.
b, a~ ad~ .
~o ~ - ~o ~ - _ _ '
dB ~ _ , -
Zo ~ zo Z
lo Jo SO g~, roaD 1v 1o D eg .SO rpa~
D ;grees al (a) (b)
Figure 4.2. The specific effective radar cross-section, Qy, of
f orested terrain as a function of the angle of beam
inclination to the horizontal,
Key: a. Temperate zone forest; b. Tropical fcrest; 1. Average value;
2. Range encampassing 10 percent of all measurements.
_ - 56 -
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPR~VED F~R RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
Figure 4.3. The specific effective radar
~,.a~ - cross-section, vy, as a func-
dg ' - tion of the angle of beam
~ , 2 inclination to the horizontal,�.
0
~ J Key: 1. Industrial regions of a city;
~ S~ _ 2. Commercial regions of a city;
-zo = 3. Residential regions of a city;
4. Forested terrain;
~ S. Broken rocky desert;
-*0 6. Sandy desert;
~o ao sa ~.�oQi
Degree~s 7. Sea f or a wind speed of f rom
5 m/sec to 7 m/sec (the larger
values of oy) .
To shield against radar detection, the return factor must be chosen in a manner
app licable to the surrounding terrain. If a road (airstrip) runs through a pine
forest, then the factor must be redueed from 60 to 29 percent, and if in open
_ f ields, down to 10 percent while among rocks, down to 49 percent etc. For this
purpose, roughness can be imparted to a conc rete surface of a road by means of
channels, the spacing between which depends on the surrounding terrain. The con-
crete surface is broken down into fields, in which the grooves run in different
I directions. The edges of the strip are camouf laged with shrubbery having a 1argP
_il scattering cross-section so as to disrupt the symmetry and distort the outlines of
i the strip.
~
i When implementing antiradar camouflage measures for various ground objects, one
must take into account the fact that the enemy has 5urveillance radars f or ground
targets and radars for detecting the fire pos itions of mortars and artillery.
I
~ The practically straight-line propagation of the ultrashort waves used in radar
limits the effectiveness of the ground station to the visible horizon. In other
I' words, by having reconnaissance data on the arrangement of enemy radar stations in
j a terrain, one can campute the boundaries of their detection areas from the well-
known formula:
I~
R = 3.57 (+~h + .
where R is the line of sight range, km;
h is the radar station antenna height in m;
H is the height of the object in m.
The positioning of objects to be probed outs ide the bounds or this zone cannot be
detected by ground radars, no matter what kind of tactical and technical data
they have.
- 57 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
Figure 4.4. The plotting of invisi-
bility fields.
Key: 1. Enemy radar posi-
Z tions;
~
_ O O 2. Invisibility
�ields of two
radars;
. 3 3. Invisibility
a f ields of one
o radar,
In many cases, the terrain relief also does not allaw the.detection of targets
by means of ground radars. Ob~ects which are concealed behind natural shields:
hills, mountains, forests - are not detected by ground stations. This circumstance,
in the opinion of foreign specialists, nakes it possible to use the terrain re-
lief on a widescale to conceal troup groupings, combat materiel, and individual
ground objecCs in the so-called invisibility f ields of the enemy radars.
Such fields can be glotted on a map of the terrain in the following manner .
(Figure 4.4) [11]. StXaight sighting lines are run f rom the locations of the
enemy radars through possible high crests, the edges of local objects and natural
shields. Then, profiles of the terrain are plott~ed using the sighting lines.
The enemy will not see in the sight profiles located behind terrain objects, since
a region of radio shadow is formed behind them which is due to the line of sight
propagation of VHF band radio waves.
3. The Masking Properties of Returns fram a Sea Surface
Signals ref lected f rom a sea surface can make it signif icantly morediff icult for
aircraft, ship or shore radars to detect targets on the water and in the air flying
at low altitude.
The nature of the average signal levels reflected f rom various sea targets and sea
waves as a function af their observation range by a ship radar is shown in Figure
4.5. It can be seen from the figure that small sea rargets (launches, small boats,
buoys or the extendable surface gear of submarines, the effective radar cross-
_ sections of which are co~nensurate with the cross-section of a buoy) will be
reliably camouflaged at certain ranges by returns from sea waves.
Sea returns have a very complex nature. The specif ic effective radar cross-section,
oy, of a sea surface depends on the angle of antenna beam inclina:.ion, the wave-
length and the radiation polarization, as well as the state of the sea and the
wind strength.
- -58-
FOR OFFIC[AL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/42/09: CIA-RDP82-40850R000400470041-5
FOR OFFIC[AL USE ONLY
Figure 4.5. The average levels of the
returns from various sea
3 targets [as a function of
40 range J .
Mi ~ Key: 1. Ship with a displacement of
i ~ 30 10,000 tOIIS;
3 ~ 2. Ship with a displacement of
E~ 20 2 1,000 tons;
~ ~ ~ 3. Sea wave clutter incoming
~A~ ~o s from a range of up to 9 km;
8 4. Clutter from a range of up
� 6
p y a 6 8 ` 1~ to 7 km;
,QaneMOtn?e, ~+unu 5 . LSUIICh;
- 6. Buoy;
by,a6 7. Limiter level;
~o 8. Range of signal variation which
dg can be displayed on the screen.
o A. Signal to noise ratio;
-ro B. Range, miles.
-zo - '
~
-30 'Ne6 c Figure 4.6. The quantity oy for a sea surface as a
cM function of the angle of inclination
of the directional pattern and the wave-
0 2o ao 6o y~,aaaa length of the radar.
, , degrees
, 6y. B~' . -
I -40 ' 1
I
I dg Figure 4.7. The quantity ay for a sea surf ace
i -Sp as a function of the beam inclin-
i 2 ation angla.
i, -so Key: 1. Quiet sea;
I ~ 2. Moderate wave agitation on
~ _~p the sea.
I ~ o,z o,a q~ t o r io ~
~ D 9~, tvQ~
-
II O,B ~r10 4 Z
, Figure 4.8. The probability of radar detection of a
! 0,6 constant amplitude pulse packet with a random
0,4 phase f or F= 10-6 .
o,z - Rey: A. Psig~Pclutter~ dB.
~ 1 4 6 8 P~
( A) ~p ~ a6
As a rule, the value of Qy increases with an increase in the inclination angle,
something which is conf irmed by the graph of Figure 4.6. The curves were plotted
from averaged experimental data f or various sea states and wind speeds which
varied in a range of from 3.7 to 45 km/hr.
-59-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
F'OR OFFICIAL USE ONLY
At small angles of inclination of the antenna beam to the horizontal < 10�),
- the dependence of Qy on the state of the sea is expressed especially sharply
(Figure 4.7). A critical inclination angle exists, ~~r, at which the slope of
the curve which which characterizes the rise in Qy with an increase in ~ changes
sharp?y. A formula has been derived empirically which expresses the quantity
cr~, for a sea surf ace as a function of the angle which yields good agreement
with experimental data:
,
a - l0e-~.g(~�-~Y"�~
r
The specif ic effective cross-section Qy increases with an increase in frequency:
in the millimeter wavelength band, it is approximately 8 to 12 dB greater than in
the centimer band (Figure 4.6). It was ascertained as a result of nimmerous experi-
ments that the specif ic effective radar cross-section o.f a sea surface is approx-
imately a a-4 function of the wavelength in the case of a quiet sea and approx-
imately a a'1 function in the case of wave agitation.
The quantity Qy is expressed as a function of the polarization in the following
manner: in the case of a quiet sea, horizontally polarized signals yield a sig-
nificantly smaller ref lection in the direction to the radar than vertically
polarized transmissions. The difference in the returns with the different kinds
of polarization decreases substantially in the presence of wave agitation.
A strong dependence of return intensity on the sea surface and sea wave agitation
is observed. With an increase in wave agit~tion, Q increases up to a certain
- limit, and then decreases. Thus, at a wavelength o~ 3.0 cm, this limit begins at
a change in the sea wave height of from 0.6 to 1 m. The quantity Qy also depends
un the direction of the wind. A reflected signal will be more intense when the
antenna be~? is directed counter to the wind. When the beam is oriented in the
direction of the wind, the return intensity will be 5 to 10 dB less.
.
0e n= Figure 4.9. The probability of radar detection
of a mildly fluctuating pulse
0,6 B packet in the case o� a Rayleigh
04 distribution for the amplitudes
(when F = 10-5).
0,1
o Key: A. Psig/Pclutter~ dB�
Z 4 F ! ~a ~ ~ 06
EA) ~
The procedure proposed in paper [40] can be used for practical calculations of
the masking effect of sea waves when detecting surface water targets with a ship-
board radar.
The problem of detecting the useful signal (the signal fram a target c+n the water
surf ace) in the presence of interf erence (sea wave clutter) is a probab ilistic
-60-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
problem. When solving such a problem, it is expedient to specify the false alarm
probability, F, at which a minimum signal passage probability, M, or a maximum
detection probability, D, is assured (the Neumann-Pearson criterion).
In terms of the processing technique for the received signals, a shipboard PPI
radar is close to the optimal proeessing system for an incoherent pulse train. The
detection characteristics of an optimum receiver with square-law summing at the
output of an incoherent packet of radar signals, n, are shown in the graphs of
Figure 4.8 and 4.9 for various F.
To segregate the useful signals in the final unit of a radar with a reliability
no less than the specified value, it is necessary that the signal/interference
ratio at the output of the detection system be no less than a threshold value
(P~/Pn)~p.
The calculation of the Psig~Pint ratio at the output of the system can be accom-
plished using the basic radar equation:
1~~ ~ a~ ( ~'~IR 1` (4.6)
` a� \ ~'~1R J ,
where aU and Qn are the probability values of the effective radar cross-sections
of the target and the sea wave agitation; y~ and Y~ are attenuation functions
[for the signal and interference respectively]; R is the range to the target being
~ detected; P~ and Pn is the back-scattered signal and interference power [respec-
~ tively] .
~
, In the special case where the observation is made at grazing angles, close to
~ the critical angl~e ~~r, expression (4.6) can be simplif ied, by reducing it to the
~ form:
i a a
' Q~ 2 ORscc t ~ (4.7)
i
i
, where 6 is the width of the antenna directional pattern in the horizontal plane;
sec ~ = h/R (4.8)
(h is the installation height of the radar antenna).
The ~uantity ~~r can be computed from the f ormula:
(hi -F- ~~~1
Sin = 292uk ' �
where hl and h2 are the referenced heights of the radar antenna and the target.
- 61 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
Values of the critical grazing angle are given in Table 4.1 as a function of the
state of the sea surface.
Based on expressions (4.7) and (4.8), one can write the condition for reliable
detection of a target and a water surface against a background of sea wave clutter:
a,~~(P� l o,lt 1 0. (4.9)
1~ ^ /~~o~,
TABLE 4.1
K~uTUhttKnfl ymn ~pR~. e~nd. ,
Cw~cTO~m~e nnnepc~a:rn wnp~ ~~p~ arnne sonn~a a. ~r /C~
Se- c. ,.c.. c~rP `
~N7AN I cpen~~a~ ~~~co� 10 ( 1 �
n n~nu, r
(A) GR) -
I (1.15 4~7 1.1
2 0.45 I,G 0.47
;1 � 0~9 0,8 0.24
I ,A Q.4 11.12
5 ~,2 0.22 0.07
b 5 0.14 U,04
7 7.fi Q.0~5 O.t13
Key: A. Intensity rating;
B. Average wave height, m;
C. Critical angle, �er, degrees, for a wavelength J1, cm.
Exa~le. We shall determine the masking effect of sea waves when detecting surface
targets with a"Don" chipboard radar having the following parameters: T= 1 micro-
second, 6= 1 degree, the pulse repetition rate is F.~ = 800 Hz, the antenna rota-
tional speed is S2 = 15 r.p.m., h= 20 m and we specify the following values: D=
= 0.9, F= 10'S and vt =-15 dB (the wave height is more than 2 m).
We find the number of pulses to be integrated:
n= 0.5 (eFn/n) = 4. n= 0.5 (eF,~/s~) = 4. ~
Fram the graph of Figure 4.9 we determine the ratio ~Psig~Pclutter~thresh. � 13 dB
substituting all of the data in expression (4.9), we obtain:
Qt > 12 dB = 16 m2.
Thus, the calculations show that in the case of sea wave agitation rated at 4 points
and above, surf ace targets having an effective radar cross-section of less than
-62-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/42/09: CIA-RDP82-40850R000400470041-5
FOR OFFICIAL USE ONLY
16 m2 c.an be detected only with great difficulty against the background of sea
wave clutter using the "Don" shipboard radar with the antenna mounted at a Height
of 20 m: launches, small boats, submarines running submerged with parascope up,
etc. And in this case, if ineasures to reduce the radar contrast are taken into
account, the masking effect of sea waves will also be extended to ships of greater
displacement.
4. The Masking Eff ect of Hydrameteors
Water vapor condensation products in the atmospher~ are called hydrometeors. They
can be observed in the form of rain, f og, snow or hail. When f alling in the target
detection field of a radar, hydrometeors reduce its detection range or mask the
- target. The masking effect of hydrometeors is amplified with a shortening of the
radar wavelength.
Hydrometeors (atmospheric precipitation) take the form of an aggregate of a large
number of individual elementary ref lectors, which fill a certain volume and which
are perceived as a single volume distributs~ taig~t.
= The elementary ref lectors which form the overall signal are distributed within the
bounds of a reflecting volume V. In the case of pulsed ra~ar, the ref lecting
volume will be equal to (see Figure 1.2):
V = ~ R~~n~e~ 2 .
Then the effective radar cross-section of a distributed volimmetri:c target can be
' found from the fortnula:
~ n ~ ct
; ap-~yv= 4 a,.R on,e,~, 2.
~
The specific radar cross-section, Q, is governed by the nature of the bulk target.
If the bulk target takes the form o~ an aggregate of hvmogeneous ref lectors -
, rain drops, hail stones, snow flakes - then the value of oy depends on the distri-
bution density of such reflectors in space, on the effective cross-section of each
of the particles, Qi, and on the polarization of the incident wave [45]. The
specific effective cross-section per unit volume of hydrometeors will be equal to:
Qy = ~ orN~, (4.10)
~
where Ni is the number of particles per cubic meter.
In the case where fogs, clouds and precipit~tion consist oi spherical water or ice
particles and their diameter is much less than the wavelength, the eff ective radar
cross-section of a particle can be camputed fram Rayleigh's well-known formula:
- 63 -
FO~' OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
' ~~d' - 1 ~ (4.11)
~ ~i~}
2)
where r. is the complex index of refraction.
For watzr, the factor +2)~ varies from 0.90 to 0.92 and depends slightly
on the temperature when a changes fram 0.8 to 10 cm. It is almost constant for
ice and is equal to 0.19.
By substituting expression (4.11) in f ormula (4.10), we obtain:
n~ ~ Nyd'
l rtx - 1 �
'Y - l~~ Cn= 2) .
It is more convenient in practice to express the quantity Qy in terms of the
water content of clouds or fogs, W in g/m3, and the rain intensity as I, in
mm/hr. Then the specific cross-sections for clouds and fogs will be:
(4.12)
~
oy -=13,2� 10-"
and for rain: .
oy _ G,2. lp-'' . (4.13)
dy.
M!/MJ
Figure 4.10. The value of the specific effecxive
~0-~ radar cross-section for rain of
various intensities.
~0~
Key: 1. Heavy rain (16 mm/hr);
~ 2. Moderate rain (4 mm/hr);
~o'� Z 3. Light rain (1 ~/hr) ;
4. Drizzle (0.25 mm/hr).
~ .
IO~p ~
0 2 * Q � e.1~,cN
rm
It follows from e~uations (4.12) and (4.13) that f or the same radar, with values
of W and I which are encountered in nature, the return from clouds and fog is
~ approximately four orders of magnitude less than the signal reflected from atmos-
pheric precipitation. For this reason, in practice it is necessary to consider
only the masking effect of precipitation (rain, snow, hail).
-64-
FOR OFF[CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
- The specific effective radar cross-section ~y, is shown in Figure 4.I0 as a
function of the rain intensity for various wavelengths. It can be seen fram the
figurQ that with an increase in the wavelengtf~, the retum from the rair. falls off~
The pvwer of the echo signal received from a target, taking into account radio wave
attenuatim, can be determined from the main radar equatian, written in the f ol-
ZOWlrig fUTID:
- Ptie~G'A!o
PR~'- (4,~~~R~. ~ r' (4.14)
where Y1 is a coefficient which takes into account the signal attenuation over the
radar-target path which is due to the influence of atmospheric gases, fog, clouds
and precipitation.
The power of returns f rom atmospheric formations is determined fron the relation-
ship:
/~~s ~G1~=ao ( 4 .15 )
pr = (4a)'Il' r''
It is proposed in tlie literature [41] that the masking effect of precipitation
be characterized by a comparative relationship between the range of a radar in
_ the absence of precipitation on the path and when precipitation is present.
In the first case, the signal to noise ratio at the radar receiver input is equal
t0 Prec~n~ and in the second case it is Prec/(Pn + Pr), where Pn is the power of
the receiver noise.
Assuming that the target can be detected at the same signal to noise ratlo, and
; euating the two latter relationships, taking into account formulas (4.14) and
(4.15) , we obtain:
/'~aAG=Aten Prerfi'l1~an1'n~
~'~R~~l~~~~Itl ~~R~~~\~ \~JlO ~ !"r~ ~
fra~ which:
R~._ R' + R'P.
n - t~~ r,
Taking into account onlq the ~asking effect of atmospheric precipitatian, we find:
- Ro = R~r~ ~ +5,2. ~D,~,,.R~ (k. i6)
The f ir~st te~ in equatian (4.16) takes attenuation into account, while the second
considers the masking return from the precipitatiax. Using the known radar range
- 65 -
_ FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/02/09: CIA-RDP82-00850R000400470041-5
FOR OFFICIAL USE ONLY
for good weather without precipitaticn, Rp, one can determine its range under
specified meteorological conditions, R, from the graphs plotted using the above
equation. Curves characterizing the change in the range of a radar with the fol-
lowing parameters in a drizzle as well as in light, moderate and heavy rain are
shown in Figure 4.11. The wavelength is a= 3.2 cm; the power per pu lse is
- Ptrans - 50 KW, the pulse width is T a 0.6 microseconds and the antenna gain is
G = 28.6 dB.
R~ MM ~
km Z Figure 4.11. The reduction in the detection
range , R, of a 3 cm band radar
so 3 for rain of various intensities.
- - Key: 1. Drizzle;
~ 2 . Light rain ;
Zs 3. Moderate rai.n;
- 4. Heavy rain.
~ 2S SO Rp~ rrM ~
_ An analysis of the curves shows that for moderate (4 nm/hr) and heavy (16 mm/hr)
rains, radar operatian is degraded quite significantly. For example, while the
range is 75 km in good weather without precipitation, moderate rain reduces it to
48 km while heavy rain reduces iC to 30 km.
-66-
~ FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
CH~PTER FIVE. ARTIFICIAL RADAR REFLECTORS AND THEIR USE
1. General Informatian
An artificial radar refleetor is understood to be a special device which is
characterized by the fact that the radar signal refle~ted from it has parameters
- which are specified beforehand (power, directionality, polarization, etc.).
Such ref lectors f ind the widest application to the anti-rader camouf lage f or
various objects: distorting the shore outline or the contours of water surfaces;
imparting reflective properties similar to the properties of surrounding terrain
to water surfaces, air strips and highways, etc. In this case, such a distorted
picture of the portion of the terrain on which th~ camouf laged target is located
can be created on the screens of ~he enemy radars that its surveillance under poor
visibility conditions will be made a great deal more difficult or altogether im-
possible.
~,rtificial reflectors play a no less important part when they are useci as decoy
radar targets. The function of such targets is to mislead the enemy, overload
his target acquisition and f ire control radar, and in the final analysis sharply
reduce the effectiveness of his fire power.
; Figure 5.1. Extent of the propagation 2ones of a
i . "cloud" of chaf f, e~ ected f rom a
i L,xN ballistic missile in various portions
i of its tra~ ectory and in various
36 directions.
Key: 1. In the plane of the trajectory
2~ � in the direction of its major
. axis;
2. Perpendicular to the plane of
~ 18 the tra~ec~ories;
~ 3. In the plane of the tra~ ectary
~ 9 in the direction of its minor
axis;
~ - tl is the end of powered phase;
t~ ~ t2 tJ t2 is apogee;
t3 is the final section.
Radar decoys, which are spaced a certain distance f rom the true target, will
attract a missile with a radar homing device to it; in this case, the probability
of destroying the protected target is considerably reduced.
-67-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-04850R000400070041-5
FOR OFFICIAL USE ONLY
One of the requisite conditions for the effective use of decoy targets is that
- they have a sufficient effective rad'ar cross-section which is comparable to the
cross-section of actual targets. In this case, changes in the effective radar
cross-sections of the decoy and the effective cross-section of the protected object
- as a function of the direction of their irradiation by the radar should be identical.
To be added to this are such requirements as simplicity of the device, economy,
small size and weight, as well as the capability of the mass utilization of decoy
targets.
Decoys are widel~ used in the protection~ ofi the most diverse military and industrial
facilities: air, s~.~ace, sea and ground installation.
An especially great effect can be achieved with decoy targets in the case of air
and space objects, primarily ballistic ~issiles. More than 50 various false targets
having an averall volume c anplexity of 100 times greater than the missile warhead
can be ejected from one missile. The extent of the propagation region of a"cloud"
of decoy targets jettisoned from a ballistic missile at various points in its
flight and in various directions relat ive to the trajectory is shown i.n Figure 5.1
[7) . The identification of a missile warhead against a background of false targets
is possible in principle, but requires extremely complex and expensive equipment.
The use of artificial radar reflectors as camouflage tools and decoy targets, in
conjunction with a reduction in the rad ar cantrast of the camouf laged objects,
makes it possible to confuse the operat i on of enemy radars to a considerable
extent.
One of the promising trends in the ref inement of various kinds of radar systems is
the increasing of their selectivity up to a level which makes it possi.ble to
- reliablydiscriminate an artificial reflector from the true target based on a set of
secondary criteria which are frequently related to the fine structure of the return.
The parameters which characGerize radar signals reflected from actual objects are
the following:
-The carrier frequency (taking into ac c ount the doppler shift in it due to the
motivn of the object) ;
--The average power and the changes in it as a function of range, azimuth and
elevatian angle;
--Tre level of fluctuations in the power (or effective radar cross-section) and
the spectral campositicm and probability distribution of the fluctuations;
--The pulse width and wavef orm;
--The polarization of the electromagne t ic wave.
It is desirable that the signal refle~ted from an artificial reflector (especially
if this reflector is used as a distrac t ing decoy) be identical to the return from
the camouf laged target with respect to the majority of the parameters enumerated
ab ove .
- 68 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
The following kinds of artificial radar reflectors will be treated in this
chapter: dipole and corner reflectors; Luneberg lenses and variants of them;
antenna arrays (Van-Att: arrays); guided decoys (both passive and with an active
respa~nse) .
2. Dipole Ref lectors
Dipole reflectors (dipoles) are one of the most widespread means of producing
camouflage jamming. They can also be used to produce individual decoy targets
(in the form of compact clouds) for the purpose of disxupting the operation of
automatic target tracking systems of radars or homing warheads.
Dipole reflectors take the form of half-wave passive antennas tuned to the working
wavelength of the radar being suppressed. If such a dipole f alls in the trans-
mission region of a radar, the frequency of which matches the resonant frequency
of the dipole, intense oscillatians are exrited in it and it becomes an electro-
magnetic energy radiator.
To obtain the resonance conditions, the length of a dipole Z is chosen somewhat
less than half of the radar wavelengths.
~ The shortening factor for the dipole is equal to:
,I
y - 2Z/a.
Strips of inetallized paper or foil (for meter wavelengths) or a metallized neutral
~ fiber or glass fiber (for centimeter wavelengths) are used as such reflectors.
~ .
The dipoles scattered in the air produce a secondary emission f ield, a portion of
the energy of which gets to the input of the radar receiver, and an intense return
will be observed on its displays, which is reminiscent of noise interf erence in
i terms of its structure.
i
' Besides producing camouflage ~amming, dipole reflectors are also used to create
~ decoy radar targets which make it difficult to observe the situation on radar
screens and which interfere with the operation of aut anatic f ire control systems
which receive inf ormation from target acquisition and indication radars.
The following conditions must be met to produce solid intense jamming with dipole
reflectors, i.e., such interference that, the camouflage target. cannot be seen on
the radar screen against such a background:
1) The intensity of the return from a dipole cloud should exceed the signal level
from the camouflaged target;
2) The signal power f rom a dipole cloud should not be signif icantly less with a
- change in the carrier frequencq of the stxppressed radar;
-69-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
_ 3) Displays of the signals reflected from dipole clouds and from the camouflaged
targets on radar screens should not be seen separately, but in the automatic
output tracking devices, it should be impossible to segregate them.
The first condition will be met if the effective radar cross-section of a cloud
of N dipoles, vN, enclosed in one reflecting volume, is equal to or greater than
effective cross-seetion of the target being camouflaged, vt.
In order to determine the number of dipoles N necessary for camouf laging any
target with an effective back-scatter cross-section Qt, it is necessary to known
the effective cross-section of one dipole, ad, and the cloud of dipole reflectors,
aN�
The following factors have an impact on the value of the effective radar cross-
section of a dipole:
--The orientation of the dipole relative to the directior. of the incoming wave;
--The polarization of the incident electromagnetic wave;
--The radar carrier f requency;
--The dipole dimensions.
It is well known that the effective radar cross-section of a single half-wave
dipole varies in accordance with the law:
rtn=O,86A~ Cos~ 0,
where 6 is the angle between a normal to the dipole and the direction to the radar.
If the dipole is arranged parallel to the electrical field intensity vector, E1,
then the intensity of the reflected electromagnetic energy is maximal and the
effective radar cross-section of the dipole is equal to:
~n MaK~! = 0.86J~~. ~d max � 0. 86a 2.
When the dipole is oriented perpendicular to the vector E1, the value of Qd tends
to zero.
We shall deterwine the mean value of the effective radar cross-section of a dipole,
when the probability is the same for any'orientation of it in space. By employing
the theorem of the mean f rom probability theory, we obtain the following expression
f or finding the average value of the effective radar cross-section of a dipole
reflector:
s, .
I '
a a(0, sin 0 dA d~.
,n ~ cs.i,
q_ae=o
. -70-
- FOR OFFIC[AL USE QNLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
The angles 6 and 9 are shown in Figure 5.2.
z~ '
- ~ Figure 5.2. On the calculation of the re-
Erz ~ dipole flection from an elemtary dipo].e
E' E: i~, B ~ Bu6Damop ' iri the case of an arb itrary
Xmit ~ ~ orientation of the dipole.
i
06nyv. ~ 0 I
f1X ' .~i Y
Receive
i~
X
G
By substituti.ng the value of a(8, in expression (5.1), we obtain:
s. .
Qn ~.0.86a' 0 sin 9d4d~
J 1
or �_n.~~
~ aa - 0,17~'.
I
! If the electrical field inten~ity vector of the incident wave is oriented parallel
to the Z axis, then the size of the electric field vector radiated by the dipole
~ in the direction opposite to the incoming wave will be determined.by the expression:
~
i E;
=:E. cos 0 sin ~N, '
' where Ep is the maximum value of the electrical f ield intensity E2 (in the equa-
I torial plane when the vector E1 is oriented parallel to the axis of the dipole);
~ ~y is the angle between the dipole and the direction in which the ref lected field
~ is observed.
I The components of the vector EZ in line with the OZ and OX axes will be equal to
the following respectively:
E27 = C, cos Y,
CZ,~ = E, sin Y, '
co~ A
But COS'( = Sin
Then /.'zZ = E. cos 0 sin cos Y= E, cc~s' 0;
F.~r=C,ccx9sin~psinY=- ~ F_,sin20cos~p.
- 71 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPR~VED F~R RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
Thus, the effective back-scatter cross-section of a half-wave dipole will depend
on the plane of polarization of the radar receiving an~enna. If the antenna re-.
ceives the vector component of the reflected electrical field E2Z, the polarization
of which is the same as in the incident wave, then the effective cross-section of
the reflector is:
- ~dZ ad max cos4A.
- In the case where the component E2% is raceived, which is perpendicular to E2Z,
the effective radar cross-section of the ref lector will be equal to:
6dX = ad max~`sin228cos2~.
We shall determine the average effective back-scatter cross-section of a cloud of
dipole reflectors. We shall assume that there are N randamly arranged reflectors
in the radar return volume. The phase relationships between the intensities of
the ref lectQd f ields of the individual dipoles, because of their random arrange-
- ment in space relative to each other and the direction to the radar, will also be
randan.
By employing the techniques of probability theory, it can be demonstrated with a
~ random distribution of the phases of the electromagnetic waves ref lected from the
dipole reflectors, the most probable value of the resulting electrical field
intensity E2N, is equal to the mean geometric value of the fiel~ intensities pro-
duced by the pairs of reflectors, i.e.:

r~ ~ E'~Eh ~
E2.v-~u lJ
!=1 k=1
where Ei and Ek are ttie field intensities produced by individual ref lectors.
Assuming that Ei = Ek = E2d, where E2d is the intensity of the ref lected electric
f ield of a single d ipole, we obtain:
r~,=E:AVN;
and the average effective radar cross-section of the "cloud" of dipoles we be
equal to:
oN = onN = ~,17x'N. (5 . 2 )
It can be seen f rom f ormula (5.2) that with a decrease in the wavelength, the
effective radar cross-section of a single dipole falls off sharply, and for this
reason, a larger number of dipoles is needed to obtain a specified effective radar
cross-section of a "cloud".
- 72 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/42/09: CIA-RDP82-40850R000400470041-5
FOR OFFICIAL USE ONLY
The number uf dipole reflectors, N, needed to simulate a target, can be determined
by knowing the aver~e values.of the effective cross-section of the target, at, and
a single reflector Qd:
N = Qt/aQd~
where a is a factor which takes into account the number of effective dipoles.
Since when dipoles are demmped fram an aircraft, some of them are broken, defermed
or tangled in clunps with the action of the opposing wind flow, the value of the
coefficient a is chosen in a range of from 0.1 to 0.3. When designing the dipoles,
an effort is made to obtain as large number of effective ref lectors as possible and
the highest rate of their dispersal with minimum wefght, volume and material con-
sumption per unit of back-scattering surface. The effective radar cross-section of
a dipole cloud, oN, is shown in Figure 5.3 as a function of the time which has
- passed since the moment they were jettisoned. A rise in the eff ective radar cross-
section was observed in the first three to four minutes. Over this time, the
dipoles fly apart and form the cloud. The cloud was produced at an altitude of
3,000 m by ejecting a packet of dipoles from the aircraft. The observation was
made using a radar at a wavelength of a s 9.2 cm [8J.
Figure 5.3. The influence of the number of
' dipoles in a cloud on the value of
_ (A) its effective radar cross-section. .
~nP - - _
N` - Key: 1. Number of dipoles (strips)
' ~ in the packet is N= 3.75 �
~oJ � 106, horizontal polariza-
' tion of the receiving
- antenna;
~ tOr " 1
, 2. Number of dipoles in the
, - packet is N= 0.625 � 106,
- vertical polarization.
~ 2 v 6 e ro r2 .+o A. Effective '~ack-scatter cross-
epeM~ om MoMeNmo c6pacuecNU,~ sec t ion, m2 ;
navexplNn'?,HUM (B) B. Time from the moment the
packets of chaff are
jettisoned, minutes.
As was stated above, the resulting signal ref lected from the dipole cloud takes
the form of the sum of signals which are randam in phase and amplitude from a large
number of reflectors. Therefore, the amplitude of the resulting signal from one
repetition period of the radar probe pulse to the next does not remain constant, but
changes with time in a randam manner.
-73-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPR~VED F~R RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
An experi.mental study of returns from a cloud of dipole reflectors showed that the
spectral width of the amplitude fluctuations in the reflected signal is governed
by the rate of motian of the dipole relative to each other and relative to the
radar statian, as well as by the wavelength of the transmitting radar.
It can be assumed with sufficient precision that the distribution of the dipole
velocity and the spectrum of the returns f~om them obey a Gaussian law. For this
reason, the spectral width of the returns from the dipoles is
Sf0.5 = S (vd/~) .
wt~~ere dfp,5 is the half-power spectra? width, in Hz;
vd is the average rate of dipole travel, cm/sec;
a is the radar wavelength in cm.
- fihe width of the fluctuation spectra can range from tens to several hundreds of
hertz. For example, it is 10 to 40 Hz at a frequency of 3,260 MHz (Figure 5.4).
Figure 5.4. Spectra of the return from dipole chaff in the
centimeter band (f = 3,260 MHz).
w(>)
Key; 1. When the dipoles are dumped from an
J,0 aircraft and when the wind speed is up
to 40 1~/hr;
05 2. When the dipoles are dumped from an air-
3 Z ~ craft and the wind speed is about 16
Hz km~hr~
~ 2~ h0 en eo a'1,rq 3. When the dipoles are dumped from a
slawly moving dirigible.
Usually, glass f iber or metallized strip dipoles are packaged in a packet in such
a number that each packet simulates the actual target in terms of its reflective
properties. To produce ~amming interference f or radars operating at meter wave-
lengths, it is suff icient to have a few tens Af inetallized strips in a packet.
For counter measures against centimeter band radar, the number of dipoles in a
packet runs up to tens of thousands.
When camouf laging a certain space, such a number of ref lectors should be ejected
into each reflecting volume that their total average effective radar cross-section
is equal to or greater than the total effective cross-section of the targets being
camouflaged which are located within this volume.
In this case, with any position of the radar antenna within the bounds of the
selected zone, the returns from the dipoles in one reflecting volume will be
-74-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY
observed on the display sc~een to merge with the returns from dipoles in adjacent
reflecting volumes.
The number of dipole packets, n, which must be dumped into each reflecting volume
to effectively camouflage the targets being protected, can be determined from the
- formula: ~
, n = (Qtm/QN) n
where QN is the average effective back-scatter cross-section of a dipole packet
_ cloud;
Qt is the effective radar cross-section of the target being camouf laged;
m is the number of targets falling within the ref lecting volume which are
being camouf laged;
~ n is a safety factor which takes into account the fact that not all of
packets dumped from the jamming vehicle will open up.
The timewise interval for dumping n packets of N reflectors to produce a
solid jau~ing f ield on the screen of a radar display depends on the resolving
volume of the radar, Vp, which is gaverned by the range resolution of the radar,
~R, and the angular coordinates De). The greater the resolving volume, i.e.,
the worse the radar resolution, the smaller the number of dipole packets which are
' needed to suppress the radar. ~
~ Packets of reflectors which form discrete compact clouds of dipoles are thrown
~ frvm the jamming delivery vehicle (or from the object being camouflaged) to
, produce the false radar returns.
! One of the major drawbacks to dipole reflectorsas a means of antiradar camouflage
consists in the comparatively small time they act on the radars being suppressed.
~ This time depends on the ejection altitude of the dipoles, their rate of descent
~ (approximately 40 to 50 m/min), as well as on the wind speed and can reach several
- tens of minutes, being considerab ly reduced in rain or snow.
' The cloud formed by dipole reflectors of the same length produces a masking effect
in a narrow range of frequencies: the bandwidth does not exceed 5 to 10 percent of
the center frequency. The bandwidth can be extended by increasing the length and
width of the dipoles or by putting together packets of strips of different lengths.
Naturally, the material consumption increases in this case and the ref lector
production technolog~ becomes more complicated.
Dipole reflectors were used f or the f irst time as a means of antiradar camouflage
by En~lish air forces during an attack on Hamburg in July of 1943, and were widely
used thereafter by the belligerents during the course of the Second World War.
= Dipole reflectors were manufactured from foil or metallized paper.
-75-
FOR OFFICIAL USE ~JNLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
The English and American air forces dropped more than 20,000 tons of aluminum foil
rn~er German territory ~uring the war. The Germans themselves acknowledged that as
a result of the comprehensive use of active jaIIaning and dipole reflectors by the
allies, the effectiveness of German air defense was reduced by 75 percent. Accord-
ing to data on the foreign press, the use of such techniques made it possible to
save about 450 aircraft and spare the lives of 4,500 flight crew members f rom just
the American Airf orces operating in England.
In additian to half -wave dipoles, locig metallized strips (up to 120 meters long)
were also used, which were dropped fram aircraft on special parachutes. During
the Second World War, packets of dipoles or long metallized strips were thrown out
manually by crew members. However, a special automatic device was designed as
early as the end of the war. Then shells, mortars and rockets filled with dipole
- reflectors were use~ for the first time. Such 82.5 mm caliber rockets were used,
in particular, from launch positions on allied ships during the invasion landing
in Normandy in 1944. Some 76,800 metailized strips from 12.7 to 406 mm long were
placed in the w~rhead of a rocket, the jettisoning of which jammed radars operating
in a wide range of frequencies.
Dipole reflectors remain an extremely effective means of antiradar camouf lage at
the present time for air and sea military objects. Work is underway abroad on
increasing the effective cross-section of dipoles, extending the frequen~~ range
and impr win g their mechanical characteristics. Foreign specialists are devoting
considerable attention to the develapment of equipment for automatically dumping
packets of dipoles fram an aircraft. Such devices are usually installed in an
external container or inside the aircraft in the tail compartment. The automatic
devices are remote control. The rate at which the packets are dumped is set before-
hand, but it can be r_hanged during the flight by the pilot.
Modern jet aircraft are much faster than the aircraft of the Second World War
period, and for this reason, they cover a distance greater than the size of the
resolution volume during the time of dipole packet dispersal. In other words, the
camouflaging aircraft, which dumps the dipoles, travels at a high velocity and does
n~t conceal itself. In order to eliminate this deficiency, special aircraft rockets
have been developed at the present time which make it possible to eject ref lectors
in front, behind, up, down and to the side.
A sma11 aviation rocket has been developed in the U.S. which is equipped with a
device for producing false radar targets by means of scattering dipole reflectors
over a specified distance. The device is placed in the nose cone of the rocket.
It consists of a tank with compressed gas, a firing pin with a trigger mechanism
intended for destroying the tank and a device which automatically separates the
nose cone of the rocket with the charge of dipoles from the rocket motor. The
replacement of the explosive charge usually employed to scatter dipoles by a tank
of compressed gas makes it possible to produce a false radar target with a more
uniform distribution of the dipoles, and moreover, ~rovides for safety when ship-
ping, storing and using such rockets in practice.
-76-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
American specialists have proposed a device for scattering dipole reflectors from
ballistic missiles. A container with the dipo}.es and a special mechanism are
mounted in the nose cone of the missile. The devic~ is actuate3 by a clock mechan-
ism after a certain time interval follawing launch. The explosion of the detanator
- following the actuatian of the device releases a spring and opens the walls of the
container with the dipoles. The clock mechanism begins to operate at the moment the
missile is launched. Special camouf lage rockets, mortar projectiles and shells are
being deveioped which can be launched from shipboard and ground installations. Thus,
a special artillery shell f~r placing false targets of dipoles has been constructed
in France. It is proposed that the shell be used to canfuse radars which determine
,the coordinates of artillery and mortar ~atteries based on the trajectory of shells
or mortar projectiles.
~n original technique of launching dipole ref lectors from a mw ing ship has been
patented in the U.S. It is prvposed that an additional mast and air blast blower
with a pipe fastened to this mast be installed on the ship. The dipoles which are
blown out form a cloud over the sea surface. It has been experimentally estab-
lished that dipoles scattered in the air provide greater returns than when f loating
on the water. Galculations show that it is necessary to immediately throw out a
large number of dipoles, approximately 6� 10~ with an werall weight of about 1 kg
to provide effective camouflage in the 3 and 10 cm bands for 1 mile of travel
(1.85 km).
3. C~rner Reflectors
A corner. ref.lector takes the form of a structure of two or three mutually perpen-
dicular conducting planes (sides). A valuab le property of corner reflectors is
their capabilit~ of reflecting a considerable portion of the energy falling within
the bounds of the interior angle in a direction opposite to the irradiation. It is
as if the corner is a mirror, the plane of which is always perpendicular to the direc-
tion of irradiation. Because of this property, corner reflectors have large ef�ec-
tive radar cross-sections, even in the case where they are small, something which
makes it possible to use them to simulate various targets:
Corner reflectors are used to create individual or group decoy targets, to increase
the effective radar cross-sections of various objects (beacons, bLOys, spar buoys,
small ships, targets, etc.), reduce the contrast of the radar image of industrial
and military installations down to the level of their surrounding background as
well as to distort the shore outlines of bodies of water.
The problem of electromagnetic energy scattering by corner reflectors was solved
by A.N. Shchukin. Despite the assumptions made in this case which simplify thQ
solution of the problem, the design formulas which were derived are in good agree-
- ment with experimental data [6].
We shall analyze the physical phenomena which are the basis for the engineering
design of reflectors with the example of the simplest (dihedral) corner reflector.
- 77 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
We shall assu~e that the direction of propagation, M, of th~ incident electromag-
netit wave is perpendicular to the edge of the ref lector and f orms an angle ~ with
- a normal to the horizontal plane of the reflector (Figure 5.5) .
At the internal faces of the corner, which are sufficiently distant from the edges,
the incident wave excites a surface current density of:
c
f ~ (;~n~l.
where c is the speed of light;
(nHi] is the vector product of the unit vector n, normal to the plane of the
side and the magnetic field intensity of the in~ident wave, Hi.
The elementary current mament of the incident wave is:
d(Ih)i � ~idS+
where dS is a surface element of a side. ~
The elementary current mament, in terms of its effect, is similar to an elementary
dipole. The direction of the current manent D(Ih)i is perpendicular to the plane
containing h and Hi (Figure 5.5). The phase shift between the elementary moments
d(Ih) is governed by their mutual positions on the sides of the corner and the
direction of the incident wave. The surface currents excited in the side of a
corner by an incident wave produced a secondary electromagnetic field which excites
secondary surf ace currents i~ the adj dcent side. The back-scattering caused by the
secondary surface currents c.orresponds to the wave reflection from the corner which
obeys the laws of optics; it has a considerable level for ineident wave directions
ahich fall in a range of + 45� around the bisector of the interior angle of the
ref lector.
It is well known that the effect of a metal surface with a d ipole arranged on it
for an actual
can be replaced by the action of a v irtual mirror image. Then,
elementary dipole d(Ih)i, which is located on side S1 of the corner, one can
construct its mirror image d(Yh)r on face S1'. The phases of the eleme~tade endinnt
moments d(Ih)i and d(Ih)r are identical or differ from eacer�endicular to or g
on whether the direction of the current moment d(Ih)i is p p
parallel with edgs takenlastthepinit ial phaseurthen theephaselofitheacurrente sur-
face of edge AB
moment d(I, h)r will be equal to:
2a
e ~j~ = ~
where ac and a1~ontroftSe,dWhichcpassesmthrough the corner reflectoraedgef ABhe
incident wave fr n
-78-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
_ FOR OFFICIAL USE ONLY
The electromagnetic oscillations produced by currents d(Ih)r in the case of omni-
directional propagation reach the planes parallel to the incident wave front, hav-
ing equal phases. In particular, their phase in the Sn plane which runs through
_ the corner ref lector edge AB, is equal to zero. In reality, the oscillations
reaching point a at face S1 lead the osc illat~ions reaching point 0 b y the
f ollowing phase angle, where point 0 fails on edg2 AB:
9 = 2n/a
i
- The current mom~nt d(Ih) at point a also has the same phase shift (lead). The
oscillations excited by the current moment d(Ih)r, reaching the Sn plane, phase
lag the oscillations excited by the current moment at point 0 by an angle of :
2a ~ . .
- e = (R,~,)�
Thus, the phase of the ~scillations excited by the current moment d(Ih)r, when
these osci"llations reach the Sn plane, will be equal to zero, since:
A, _ ~ - 9 = 2~ (nc -
, Consequently, the incident wave front Ys simultaneously the plane of the wave
-I front scattered by the dihedral reflec tor and propagating in a direction oppos ite
~
~ to the incident wave.
~
i We shall determine the density of the energy flux reflected by the corner reflecr.or
j in the direction of the transmitter. The wave incident to the corner ref lector
and perpendicular to its edge, and polarized so that the magnetic f ield intesity
I vector Hi falls in the propagation plane (Figure 5.5), excites a surface current
~ density j i having aa amplitude equal to:
~
;I
_ ~
lr, 1., Nr coa ~ e rpann Si,
' in face
~ Ny eln B r ai~u S
1~~=- 1.,= Z,~ T , �
The direction of the~e current planes is parallel to the edge AB of the corner
reflector. For this reasan, the back-scattering prodt�:ed by the secondary
currents jr in the direr_tion cpposite to the irradiati~.i can be treated as the
radiation of two dipoles located in the Sl and S2 plane having current moments of
Ii~rl a~.:j Ihr2, which correspond to the scattering of all of the elemtary dipoles
d(Ih)rl � Jr1dSi and d(Ih)r2 = ~rZdS2. �
- 79 -
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007142/09: CIA-RDP82-40854R040400070041-5
FOR OFFICIAL USE ONLY
N~
1
1 ~1
, . %
st~ M .
/
~ q ~ q ~
~ / 1
~
I
~b~DJ ~ v
~ ~
~ ~ ~
i~~ ~ ~f st
~ i~`~; 9~ Id~,h ~ .
~
\ ~ ~a1~--=~~ Q l~~' d .
B~ ~ , ~A~r c ~"1 /
St ~i~~ ~ ~ .
1
C~ Ct . A r X,
Di \ )
~ ,
_ `
. , ~ ,
S'
2
_ D
Figure 5.5. On tYie calculation of the effective radar
cross-section of a dihedral corner reflector.
These current moments are equal to:
.!h" - 2~ 1/:~ I dS'~ cos p. ~
Y
- ~~1~~ c- 2~ f~t J(f.S~~ S~J1 q.
The secondary currents, the eff~ct of which was~replaced by the effect of a fictive
mirror i.mage, flow in faces S1 and S2, and therefore the reflected waves are
emitted from these sides. Because of this, only the action of those surface
currents on face Si is taken into account, the radiation of which in a direction
opposite to the incident wave passes "through" face S2, i.e., the integration on
face Si is carried out only within the limits of the area AC2CgB.
Thus, .
rh,, 2~ H.s, ~g r ~os
~
- x,s, ~~n r, ~
- z~ .
/~i� - - 2~ //~S~ ~In T
- /h~.t = lh,~ ~h�~ _ - 2n ~ir ~s~~ $i) sin
or
-80-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFIC[AL USE ONLY
The latter expression shows that the back-scattering by a rectangular corner reflec-
tor in a direction opposite to the transmission can be replaced by back-scattering
by a flat conducting plate, D1, D2, D3 and D4 (Figure S.5), the area of which is
_ equal to the projection of the faces of the corner reflector onto the plane of the
incident wave.� The substitution of an equivalent smooth plate lying in the inci-
dent wave piane for the dihedral corner reflector makes it possible to extremely
- simply calculate the effective radar cross-section of a dihedral corner ref~ector,
Q, in any direction lying in a plane normal to an adege of the corn~r reflector:
S~
~
e - 4+~ .
The quantity S3 is the area of the equivalent plate and depends on the direction.
o� the rays impenging on the face of the corner reflector. If the areas. of the
faces are the same, Sface~ then:
S'o = 25~,~ ~~n i~ g~ ~ 2Sface sin ~
3
and the effective. radar cross-section of the corner reflector is:
S=
e - Ifit~ ~;P sin'
The resulting expression is correct for angles of ~y < 45�; when 45�, the
factor sin ~y must be replaced � cos
Strictly speaking, the methods of geometric optics can be used only in the case
where the angle between the direction of the incident ray and the bisector of the
angle between the faces does not exceed 45�. In the case of incidence angles close
to a normal to one of the faces, it is necessary to take into account the diffrac-
tion pattern which coincides with the patter4z of the plate forming the face.
A dihedral ccrner ref 1?ctor yields ~he greatest return in the case where its faces
make an angle of 45� w ith the d irection to the transmitter. In this case,
Se ~ Se max ~ Sface
and
~max $'~~Sface~~2~'
The nature of the change in the effective radar cross-section of a dih~dral re-
flector as a function of the angle between the direction of the incident beam and
- 81 -
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFICIAL USE ONLY ,
the bisector of the angle between the sides is shawn in Figure 5.6. The dashed
line in the same figure also shows the change in the reflectivity of a smooth
conducting plate with an area equal to Se. The effective back-scattering surfaces
_ of a dihedral reflector and a smooth cand.ucting surface will be equal only when
the incident angles are 0� and 45�.
~,a6 dB �
Figure 5.6. The effective radar cross-section of a
-4 ~ dihedral corner reflector as a function
-6 ~ of the angle between the incident beam
-~R t~ and the bisector of the corner.
-45 0 uS� ~(i
~
Z
~ Figure 5.7. The equivalent smooth surface,
. q, ' Se, of a trihedral corner
. ref lector in a direction which
forms the following angles with
i its faces: a= 38�30',
- ~ a d , S= 72�30' and Y= 57�10'
B,E~--------- / "s~ r ~Se/Se max = 0.86).
~ ~
.
�
. ,
A . i �
I
. ~ .
X
~ ~
IIIdX
0, 6 1 Z
~p
0, 4
0.2
� ' 2o yo eo so ~ eaQa
~e~rees
~ Figure 5.8. The curve for Se/Se ~ of trihedral corner
reflectors as a function of the direction of wave
incidence.
Rey: 1. Triangular sides;
~ 2. Square sides.
- 82 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFiCIAL USE ONLY
Dihedral cor.ner ref lectors find extremely little application in practice, since
they scatter a cansiderable portioa of the energy in the direction opposite to the
transmissian, where this transmitted raditian is in plane perpendicular to an edge.
This defficiency of a dihedral corner has been eliminated by adding a third side,
perpendicular to the two others.
The cal~ulation o~ ehe effective radar cross-section of a~rihedral corner reflec-
tor is ~arried out in a manner similar to the case cansidered above, i.e., by
means of f inding the area of the equivalent smooth surface Sa. The equivalent
smooth surface is plotted in Figure 5.7 for a trihedral right-angled corner reflec-
tor.
For such ref lectors, the maxi.mum of the reflected energy falls in a direction which
- forms the foll a~ring angles with its sides: a= S= Y= 54�45', i.e., when
c~s a= cns a- cos T__ ~/Ir~.
For this direction, the equivalent smooth plate areas, Se are equal to:
a2/~ for a reflector with triangular sides, and
a2~ for a reflector with square sides, where a is the edge length of
- the trihedral reflector.
~
~
~ The relative value of Se/Se ~X is plotted in the graph of Figure 5.8 as a functian
, of the directions of the incident wave, which fall in a plane normal to one of. the
sides, when a = 6.
' The maximum values of the effective radar cross-sections of trihedral corner re-
' felctors are determined by the following formulas:
1) For reflectors with triangular sides: ~
4 +~n� .
0-3
~ 2) For re~lectors with sides in the form of right-angled sectors of a circle:
a _ 16 ,vt~
3
3) For ref lectors with square sidee:
o = 12 .
-83-
~ FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
Thus, tae effective radar cross-sections of comer reflectors with triangular,
circular and square sides, given the same edge length, are in a ratio of 1:4:9.
- These ratios, which are derived f rom the laws of geometric optics, will be correct
only with the sufficiently large dimensions of the sides as compared to the wave-
length.
Since the effective radar cross-section of a comer reflector is proportional to
a4, the detectian range of such reflectors by radars will be proportional to the
linear dimensions of the corner edge for the case of free space. In other words,
a corner ref lector with an edge length of a= 2 m will detected by an aircraf t
radar at twice the detectian range of a corner r~f lector with an edge length of
1 m. It can be seen f rom the formulas cited above that corner reflectors can be
used effectively an in the centimeter and millimeter bands.
The effective radar cross-section of a corner ref lectar with square sides is nine
times greater than that of a reflector with triangular sides, given the same size
of a side a, although the only half as much metal is needed for the fabrication
of a reflector with triangular sides. Hawever, the reflector with triangular sides
has a wider directional pattern for the secandary emission, and moreover, its con-
struction is sturdier.
The major characteristic of a corner ref lector is the dependence of the effective
radar cross-section on the directian of the incoming incident wave. Experimental
data show that when the irradiation angle changes by +(20 to 30) degrees with
respect to the optimal, the effective radar cross-section of a corner reflector
falls off by 8 to 10 dB. Cor.tpensated corner ref lectors are used to produce a more
uniform directional pattern (Figure 5.9a)'. When the angles ~ and 9 between the
incident ray and the bisector of the corner angle exceeds 30 degrees, electromag-
netic waves start to be ref lected from the additional compensating ref lectors also.
It can be seen from the graphs shown in Figure 5.9b that the use of additional
reflectors substantially increases the level of the refle~ted power. The ratio of
the dimensions b/a governs the degree mf campensation. The optimum ratio is
b/a = 1. If the quantity b is high, then so-called overcompensation begins and
there is a trough in the center of the ref lector back-scatter pattern.
Corner reflectors are frequently set up on the surface of the ground or water. In
this case, it is necessary to take into account the inf luence of the separation
surface on the back-scatter pattern of a corner ref lector in the vertical plane,
which ~akes on a multiple lobe character. For better observability of such a
reflector, it is necessary to incline it in the vertical plane. The inclination
angle is chosen depending on the direction in wh~:ch~~.it is necessary to have the
maximum reflected energy. Thus, for example, this angle is 35 degrees f or ship
radars. The inclination angle must be chosEn in a similar manner to produce the
maximum return for aircraft radars located at a great distance from the corner
ref lector.
Special structures of several comers are used to provide an intense re~urn in all
directions fram a false target made of corner reflectors.
-84-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R004400070041-5
FOR OFFIC[AL USE ONLY
A widespread design is the so-called octahedral group. It can be put together
f ram three flat metal sheets, arranged so that they f orm eight trihedral corner
ref lectors. Depending on the position of such a group relative to the transmitCer,
various reflection patterns are obtained (Figures 5.10 and 5.11).
a
1
~ '
tl , , ~ ~ !p~ B
i ~
o) ( a) ~
50 .
op ~
20 ~0--40 Sp~O'
pq~ 0
~ j 69
~~40 -
N~a 20
r+i o Sp=-JO� Sp_Jp� '
I V
~ 60 �
I Go40
; a~za ~ .
~ a ~=-to ~=2v
4
~ ua 60
a~ .
i w ap
' ~ =-AD S0=J0"
' v0 ?0 0 10 B' 40 ZO 0 10 40 B'
' � Cb)
i
Figure 5.9. A trihedral corner reflector with ~upplemental corners (a)
and the return patterns (b). The solid lines in the graph
apply to a reflector with supplemental campensating corners;
the dashed lines apply to a ref lector without the campensating
corners .
A more uniform reflection patCern can be obtained in the horizontal plane by means
of a group of five trihedral corner reflectors, arranged in a circle (Figure 5.12).
In the group of five ref lectors, all of the axes of symmetry are arranged in one
;~orizontal plane, and for this reason, the effective radar cross-section of such a
- R5 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R000440070041-5
FOR OFFICIAL USE ONLY
group is approximately twice that of an octahedral group and the main lobes of
the-reflectian pattern are of greater width.
It is impossible in practice to obtain an omnidirectional return pattern fram a
stationary strncture of corner ref lectors which would not have numerous maxima and
minima because of interference. For this reason, structures made of a group of
corner reflectors are employed, phich rotate in the azimuthal plane. The cut-up
nature of the return pattern is smoothed out considerably in this case (Figure
5.13). The number of revolutions of such a structure depends on the type of
- oscillations generated by the radar transmitter, In the case of CW radar, a few
revolutions per minute are sufficient. In the case of pulsed operation, the
~ ntanber of r. p.m. of the reflector should be 25 to 50 percent of the pulse repeti-
tion rate [37].
o�
1
Z
270~ - 90'
_ , .
~
a' (a) S~ (b)
tao�
Figure 5.10. Group reflectors. Figure 5.11. Patterns of the returns
from the group ref lectors
Key: a. Made of cells with depicted in Figure 5.10.
square sides;
b. Made of cells with Key: 1. With square sides;
triangular si3es. 2. With triangular
sides.
One of the major requirements in the fabrication of corner reflectors is the pre-
cise observance of the perpendicularity of the sides. Even a slight deviation of
the angle between them from 90 degrees can produce inter�erence phenomenon which
significantly re;iuce the size of the effective back-scatter cross-section. The
1 reduction in the effective cross-section with a deviation in the interior angles _
of the corner reflector from right angles is explained by the disruption of the
in-phase nature of the field in the aperture of the reflector because of the dif-
ference in the travel of the rays. The relative effective radar cross-section of
a corner reflector with triangular sides is shown in Figur.~e 5.14 as a function of
the precision of its fabrication. The greater the linear dimensions of the sides,
the more precisely the angle of 90 degrees between them should be maintained
(Figure 5.14). This is one of the drawbacks to corner reflectors. The effective
- 86 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPR~VED F~R RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR nFFICIAL USE ONLY
radar cross-section of a corner reflector increases with increasing size of its
sides, a, given a def inite error in the manuf acture, and a constant wave-
length, a.
~ o' p�
~
170 - 9L ?70 ~ 90�
~
~
~
.
lg0� .
- . ~80�
Figure 5.12. Pattern of the retum in a Figure 5.13. The pattern of the return
' horizontal plane from a f rom a f ive cell corner
i f ive cell corr:ar reflector. reflector when it contin-
uously rotates in the
azimuthal plane.
I
~
I ~
6 ~ d6 dB
6NaKc
~ a -10
~ ~ ~
, ZD ~ ~ Figure 5.14. The effective radar cross-sectian of
~ _20 / ~ a trihedral Corner reflector as a
; yp ~ function of the angle between the
I', B9 90 oG,zpaB deg' sides for various ratios of the edge
length to the wavelength.
It can be seen fram the curve shown in Figure 5.15 that there is a limit beyond
which it is not expedient to increase the dimensions of a ~orner reflector for a
given fabricatian precision 0. For example, with an error of 0= 0.5 degrees
( a= 89.5 degrees), the ultima'e length of a rib amounts to amaX s 60~.
For corner reflectors with large dimensions ~f the sides, the deviation of the
angle between them from 9Q degrees should not exceed 0.5 degrees - 1 degree.
- 87 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
In a trihedral corner reflector, the incident
~r d wane is reflected from the three planes, each
sooa - of which changes the direction of rotation of
3000 , wave polarization to the opposite direction.
- ~oeyzonbNb+e znawu If the radar antenna is circularly polarized
200o ri g lar Si e ~
~ with a right-rotation, then because of the
~ooo odd number of reflections from the faces of
. ' the corner ref lector, the reflected f ield will
soo have a lef t circular plane of polarization,
30o g9S, and consequently, the radar will not detect
zoo , such a target. Various steps are taken to
' gy~ eliminate this phenomenon, which reduced to
ess the f act that the property of a so-called
so asymmetrical target is imparted to the corner
- ,8 ref lector.
~o -
The sjmplest w~ay ef designing a corner reflec-
Q tor f or circularly or elliptically polarized
ZO 30 40 70 ~
radars consists in placing a dielectric plate
in front of one of the sides of the reflector
_ Figure 5.15. The relatianship be- a slight distance from it, as shown in Figure
tween the precision 5.16. Because of this plate, the phase
in the fabricatian difference between the horizontally and
- of a corner reflec- vertically polarized components, the wave
tor and the dimen- energy ref lected from the instde plate is not
sions of the sides. 90 degr�es, but falls between 0 and 180
degrees. As a�result of the addition of this
wave to the camponent of the field ref lected
at the sama point in time from the outer
surf ace of the plate, elliptical polarization of the wave occurs, which can be
broken down into two waves with circular polarization in diff erent directions and
different amplitudes.� The thickness of the plate and the spacing from the metal
side is determined experimentally.
A wdiespread type of ref lectors for radars with circular polarization is a corner
~ reflector, in the aperture of which an arraq of parallel wires is placed. This
reflector will be a wideband one for circularlq polarized waves. ~t has the same
return pattern as the conventional trihedral reflector, hawever, its effective
radar cross-section is 6 dB less. Moreover, such a reflector back-scatters a
field with linear polarization just a corner reflector does only in the case where
the polarization plane of the incident wave is at an angle to the elements of the
array. However, if the electrical field vector lines up with the direction of the
wires, then the reflector will behave as a flat plate having an area equal to the
aperture of the corner reflector. This drawback can be eliminated if the wire
arrays are not placed in the aperture of the reflector, but rather in front of its
sides a~ a spacing of ~/8 from them. When both linear components of a circularly
polarized wave, which are shifted relative to each other in time and space by 90
degrees are reflected from one of the sides with such an array, they receive an
additiotial 90 degree shift, because of which a linearly polarized wave appe:rs.
- - 88 -
FOR OFFICIAL USE ONL~Y
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2047/02/09: CIA-RDP82-00850R000404070041-5
FOR OFFICIAL USE ONLY
Zt can be broken down into two waves with circular polarization in opposite direc-
tians, of which only one will produce a~ip on a radar screen. In contrast to a
reflector with an array in the aperture, this structural design is a narrow-band
one, i.e,, it operates only in a def inite range of frequencies.
A variant of the comer reflector is the biconical reflector (Figure 5.17). It
has a unif orm circular secondary emission pattem in the horizontal plane. The
effective radar cross-section of such a reflector when the polarization plane of
the field is parallel to the axis is the same as for a cylinder of radius:
ravg = ~1/2)~rmax + rmin~
a:~d having a height h, i.e.:
_ Q = 2nra~gh~/a2.
rt,,;~
t=15 y ~,Oo~3A~
~ Figure 5.16. A corner ref lector f or radars
using circular polarization.
J,/dMM ~
I ~=t~5~ 0.~00~~ ,
i p~~; ,~a
~ s,uaMN mm .
II
~ The fabrication of such re~f~.ectors with the requisite precision is quite diffi-
II cult, and for this reason they have not yet found mass application.
! We shall now touch upon some questions of the use of corner reflectors for the
~ purposes of antiradar camouf lage.
A is well known, when scanning the ground or sea surface, the intensity of rzdar
_ returns is governed by the distributed targets which have significantly difS`erent
reflective proFerti.3. Modern aircraft radars make it possible to discriminate
the outlines ~f cities, large industrial enterprises, railroad centers, contrast-
- ing objects (with respect to the intensity of the radar return) (rivers outlining
~ities, bridges, dams, etc.), as well as individual and group targets. Using
co2ner reflectors, one can distort the image of such objects by means of changin.g
the reflective properties of indi�~idual sectians of the ground or water surface.
The major goal which is pursued in this case is a reduction of the radar contrast
of the camouflaged objects down to the level of the background surrounding them
by virtue of increasing the effective radar cross-sections of individual portions
of the surface, where such objects are located. Since irradlating a certain
- 89 -
FOR OFF(CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R000440070041-5
~ FOR OFFICIAL USE ONLY
section of a ground or water surface can he acca~p?ished from any direction, it is
essential for effective camouflage that the intensity of the additionally produced
return is practically independent of the irradiation angles in the horizontal and
vertical plane. This can be accomplished o same extent through the use of group
corner ref lectors, the structural design of which was treated abave. Since the
reflectivity of a portion of a water or ground surface is governed by the effective
radar cross-section of the resolvirtg area, Qf, then for successful camouflaging of
an object using corner ref lectors, it is necessary to meet the condition ot < Qf�
It is ..pparent that depending un ti:e dimensions and conf iguration of the section
being camouflaged and its reflecting properties, a various n~ber of carner reflec-
_ tors can be set up per unit area with a definite arrangement and dimensions of them.
? To produce decoy targets, the number
g~ of corner ref lectors and their dimen-
sions must be chosen so that the
~ ~MU ~ total effective radar cross-section
h 90� in, ~ is equal to the cross-section of
~ the actual target. The spacings
~__1 ~ between the ref lectors are chosen
~ equal to or samewhat less than the
~o~c resolving power of the radar.
a) (a)
0 50 Corner ref lectors found widescale
~ practical application for the first
n~ 1o time during the Second World War.
~1) aN zo Thus, German submarines, in evading
0 3,o pursuit when running deep,.using them
a o ~ � to distract antisubmarine ships and
�-so-a~ ;~o-zo -~o a ro 7u ~o 0o e aircraft in a false direction. The
6) (b) reflectors were thrown out in special
I gigure 5.17. The structural configuratian buoys or were suspen3ed from an air
(a) and pattern Qf the returns balloon.
(b) of a biconical ref lector In order to conf use the enemy about
(rm~ = 5 cm, rmax ~ 43 cm). the true number of large submarines,
KeS~: 1. Ref2ected signal as weil as to disorient him relative
level, dB. to the direction of the main thrust,
_ corner ref lectors were installed on
- ships, launches or towed ships. Such
a method was used, for example, to disorient the enemy radar and distract the
Ge~an attack aircraft f rom the main assault landing forces during the landing of
the Allies in Europe at the end of the Second World War. Groups of small ships
approached the French coast in the region of Baulogne from pointa which were widely

~ separated from each other. The ships towed aerostats painted with aluminum paint
and carried corner reflectors on themselves which simulate the returns fram large
battle and landing ships. Small groups of aircraft dumping packets of dipole
ref lectors and actively jamming German radars continuously flew over these ships.
The demonstration continued for about four hours and the impression was created
among the Germans that 3 large number of sea and air forces were approaching the
- 90 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFIC[AL USE ONLY
egion of Boulogne. Trusting the reality of the decoy measures, the Gezmans sent
their main forces to this region.
During the air attacks of the English and American bomber forces pn Berlin, the
numerous canals and lakes in the features of the city served as good landmarks.
during the bombing. To reduce the effectiveness of bambing strikes on the capitol,
- the Gex~ans set up a large number of flaating corner ref lectors on the surface of
the lake. They were constructed fram two vertical, mutually perpendicular metal
planes, installed on a floating wooden cross. The water surface served as the
third reflecting plane. The reflectors were placed on anchors at spacings of 100
to 150 m. In the majority of cases, the water surf aces were not completely camou-
flaged, but were used only as partial antiradar camouflage and to break the lakes
up into sections.
Because of such camouf lage measures, numerous night air attacks of the English
- and American air forces proved to be unsuccessful. There was an instance where
about 100 four-motor aircraft dumped their load on an accumulation of 100 corner
ref lectors, set up on one of the Berlin lakes.
Similar measures were taken to protect locks and dams in the port cir.ies of the
North Sea. The main purpose of these measures was to smooth out the contrast
between the shore installations and the water surfaces on the screens of the radars.
Corner reflectors of rather large size were used in individual cases. Thus, for
example, to "balance out" the radar image of air f ields located in the vicinity
of Berlin, corner reflectors with sides of 10 x 10 m were set up agains~the back-
_ ground of the terrain and structures of the city. In ordsr to reduce the wind
loads, the reflecting planes of the corners were �abricated from.wire netting.
By the end of the war, the Germans had simulated the city of Kuestrin with corner
reflectors; two cities were observed at a spacing of 80 ktn from each other on the
screens of aircraft radar, something which naturally disoriented the radar oper-
ators.
Corner reflectars were also used to camouflage comparatively small ground facili-
ties. It.~aas reported in the West German press that a decoy target consisting of
50 large corner reflectors fully proved itself in action where the decoy was
located close to a powerful electric power station. During poor visibility, this
decoy target attracted the attention of radar operators i.n the English and American
air forces, which dropped bombs on it.
Despite the design of such new Effective radar reflectors as Luneber lenses,
passive arrays and others, corner reflectors still remain in the arsenal of anti-
r~dar camouflage tools. Their major advan~age as compared to other similar
devices is the structural simplicity. When designing corner reflectors, the fol-
lowing major requirements aX2 pla~ed on them:
--Low weight;
--A minimimm of assem'oly components;
- 91 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00854R000440070041-5
FOR OFFICIAL USE ONLY
--Si.mplicity of the fabrication technology;
--The capability of being transported over various distances.
4. Luneberg Lenses
A structure made of several corner reflectors, as was shown above, nonetheless
leads to a nonuniform secondary emission pattern. Another drawback to such designs
is the fact that their effective radar cross-section, averaged over all possible
directions, falls about 7 dB below the maximum eff ective radar cross-section of a
corner reflector. Ideal omnidirectional reflectors are metal spheres, however,
their effective cross-section is quite small.
v v
~ Figure 5.18. Trajectory of the rays in .
0 a Luneberg lens.
al (a) ~b) ~ . .
A quite effecti�re, though still expensive reflector is the so-called Luneberg ler~s.
Such a reflectoc makes it possible to obtain an effective radar cross-section
pattern in a ~;der range of azimuths and elevation angles than any of the corner
reflectors t~~eated in the preceding section. The lens takes the form of a sphere
made f=:,.~ a dielectric. One hemisphere of the sphere is metallized (Figure 5.18a).
The dielectric permittivity e of the outer layer of such a reflector is close to
the value of the dielectric permittivity of air and graducally increases with in-
creasing thickness of the layer. Because of this, the lens focuses a parallel
bundle of rays incident to it to a point on the metallized surface of the sphere
and reflects this bundle in the opposite direction, parallel to the indicent rays.
When one hemisphere of the lens is metallized, it uniformly reflects the energy
impinging on it within the limits of a spatial angle of 140 degrees.
The law guverning the change in the dielectric permittivity e and the index of
refraction n is determined by the following relationship: ~
E=n2=2-a2,
where
a = r/r0,
(re is ~Lhe radius of the sphere; r is the distance from the center of the sphere
to the point on the sphere under consideration).
The effective back-scatter cross-section of a Luneberg lens is camputed f ram the
f ormula:
-92-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE ONLY
Q = n3d4/4a2
where d is the lens diameter.
tt has been reported in the press that a Luneberg lens mounted on a fighter
increased the intensity of the radar return from it by a factor of 40 times.
It is possible in principle to design an omnidirectional lens reflector, the re-
flection factor of which is independent of the direction of the incident electro-
magnetic wave. If the incident ray, in bending inside the lens, approaches the OX
axis at an angle of 90 degrees (Figure 5.18b), then by virtue of the spherical
symn~etry, it will be bent in the lower half of the lens through another 90 degrees
and exit in parallel with the incident ray. In this case, there is no need of
:netallizing a portion of the sphere and we obtain a variant of the Luneberg lens,
the so-called Eron Lippman reflector. There is yet another important difference
between the Luneberg Iens with a metallized shield and the omnidirectional reflec-
_ tor considered here. It they are both irradiated with a circularly polarized
wave, then the former reflects the polarized wave with the opposite sign while the
second reflects it with the same sign as the incident wave.
The law governing the change in E and n in such a reflector is determined by
the expression:
e = n2 = ~2/a) - 1.
'
I The index of refraction n in the center of the lens should tend to infinity,
~ while at tne exterior surfac e, n= 1.
' .
;
~
, T
j
~
Figure 5.19. A Luneberg lens con~isting of hanispherical shells,
with discrete changes in:~the index of refraction.
It is very difficult ia practice to realize a continuous change un the index of
ref rac t ion f rom unity to inf inity. Actual lens ref lectors are composed of a large
number of spharical shells, each of which has a constant index of refraction.
- 93 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400074441-5
FOR OFFICIAL USE ONLY
The discrete changes in the index of refractian approximate a continuous change
in it. Thus, a practical problem in the fabrication of Luneberg lens type reflec-
tors is the d~termination of the number.of spherical shells and the amount of
change in the dielectric permittivity in each of these shells.
Polystyrene foam, the index of refraction of which depends on its density, can
serve as a material f or the manufacture of such lenses.
A sample of a multilayer spherical Luneberg lens, manufactured in the U.S., is
shown in Figure 5.19. The lens consists of concentric dielectric shells, arranged
one inside the other. The dielectric permittivity of the individual shells varies
in a range of 1.1 2, with increments of 0.1 each. The diameter of such a lens
with a stepw~se change in the index of refraction is about 46 cm, while the working
frequency is in the 3 cm band.
A large number of the most diverse lens ref lectors has been developed based on the
Luneberg lens. Thus, a reflector which is omnidirectional in azimuth can be
obtained by encircling a Luneberg spher~ with a reflecting metal ring, as shown in
Figure 5.20. The position of the ring relative to the equator of the sphere de-
termines the position of the main lobe of the directional pattern with respect to
the horizontal plane. If the ring is centered relative to the equator of the
sphere, the maximum of the pattern falls in the horizontal plane; if the ring is ,
shifted, the elevation angle will be greater. With an increase in the width of '
the ring, the width of the directianal pattem in the elevation angle plane also
increases, but in this case, the amplitude in the apertvre of the reflector falls
off.
The maximum value of the effective radar cross-section of such a reflector can be
approximately,determined from the expression:
aMe n~ _ ~ ~*r' - 2rL)',
where r is the radius of the sphere and
L is the width of the ring.
A broad directional pattern in the vertical plane with a minimal reduction of
the amplitude along the aperture can be obtained by means of so-called "helisphere",
which is practically speaking, a modification of a reflecting shield, covering one
of the hemispheres of a Luneberg lens. A helisphere can be obtained by replacing
_ the solid metal ring with an array of parallel wires, wound at an angle of 45
degrees (Figure 5.21a, b).
If you look from the center of the sphere, the wires wer the entire horizon will
be arranged at an angle of 45 degrees. However, if you look at such a teflector
fram the outside, then behind the exterior surface wires, which are arranged at an
angle of 45 degrees, there are the rear surf ace wires which are perpendicular to
them and which have an inclination angle of 45 degrees to the horizontal. Thus, if
a plane wave with polarization of 45 degrees reaches the front surface, passes
through the wire grid without losses until it reaches the rear ref lecting surface,
- 94 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFEIt[AL USE ONLY
- r ~ ~
Figure 5.20. An omnidirectional Luneberg rs-
~ flector (in the azimuthal plane)
� with a metallic ~ring.
z ~
s Key: 1. Ring;
2. Plane om~idir~ctional
reflection pattern;
3. Conical pattern.
_
~~~~\\\\\\11~ ~
~b~b1 Figure 5.21. Vario~ts kinds of omnidirectiona~ Luneberg
(a) Q) lens reflectors.
_ ~
\
(c) 8) ~d~')
; and if the gaps between the wires of the "helisphere" has been chosen correctly,
i it is focused to a point locatea approximately half way on the radius of the
~I sphere. The use of two orthogonal rings of wire arrays to obtain an isotropic
pattern in the azimuth and elevation angle planes is shawn in Figures 5.21c and d.
I The advantage of such reflectors is th_e fact that their effective radar cross-
section remains approximately the s~me both for circular polarization and f or
horizontal or vertical polarization. The polarization losses with the double
~ travel through the lens will amount to no more than 6 dB (as cam~ared with 45
degrees polarization), and they can be compensated by a slight inc~rQase in the .
- dimensions of the reflector.
- At the present time, it is considered extremely expedient to use hollow spherical
- reflectors instead of heavy Luneberg lenses. In them, the dielectric sphere is
( replaced with a hollow helispherical array, within which a reflective metal ring is
I placed coaxially with the helisphere at a spacing equal to t:~e focal distance,
_i where this metal ring takes the form of a spherical segmen,c having a diameter equal
; to approximately half of th~ diameter of the outer spherp. (Figure 5.22).
I' The width of the relfecting ring, w, governs the width of the directional pattern
of the reflector in the elevation plane. Consequently, when choosing the width
of tne ring, it is essential to achieve the optimal ratio between the width of the
pattern in the elevation (vertical) plane and a permissible reduction in the
amplitude over the aperture of the ref lector.
The main requir~ments which the structural designs of hollaw helispherical reflec-
tors should meet are as follows: high fabrication precision for the spherical
surf ace, high precision in the angular position of the array wires, minimal
- 95 -
FOR OFFICIAL USE ONLY .
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/02/09: CIA-RDP82-00854R000400070041-5
� FOR OFFICIAL USE ONL,Y
d ~
2
- 3 ~ I Figure 5.22. A hollow helisphere reflector.
Key: 1. Hollow transparent ~
. sphere;
- - 2. Array os parallel wires,
wound dt an angle of
_ D ~ 45 c~egrees;
3. Metal ring with a
diameter of d = O.SD.
_ � o
JJO� J~ o
2' ~ . , ~ - `i JO� ~p JO�
3~0� V _ 6Ue 10
60� 30 50�
; i. . , ~ ~0
270�~ i90� ~ ~
. ~ -
- - ~ 90, - 9~�
' / ` ~
z~p ~ ~ 170�, `
~ r
.
` ~
- 110~~'~ ^ l50�
' ~9~�
~ Figure 5.23. Patterns of the return in Figure 5.24. Diagram of the return in the
~ a horizontal plane from a vertical plane from a hollaw
hollow helisphere (1) and a helisphere.
corner ref lector (2) .
_ dielectric losses, minimal internal impedance at microwave frequencies, high
mechanical strength, low weight, low cost and stability with respect to climatic
factors.
The reflection pattern of a hollow omni.directional helispherical reflector with a
diameter of 609 ~ and a_:tructure consisting of s{.x corner reflectors, inscribed
- in a sphere with a diameter of b09 mm are shown in polar coordinates in Figure 5.23
for comparison. A grid of nichrome wires arranged par~allel to each otfier with an
angle of 45 degrees to the horiz~ntal was used in t~he r.onstruction of the heli-
spherical reflector. The wires were pressed into a fibErglass base; the spacing ,
between the wires is 1.6 mm. The secondarq emission pattern of the helisphere for
a refleeting ring 76.2 mm wide is shown in Figure 5.24. It has been experimental.ly
determined that the optimum diameter of the reflecting ring.for the given heli-
_ sphere should be 355.6 mm. The effective radar cross-section of the reflector when
the ring diameter is reduced down to 304,8 mm is cut almost in half. The reflector
weighs 3.175 kg. It can be seen from the graph of Figure 5.25 that the effective
radar cross-section of a helisphere with a reflecting ring on the inside is
-96-
- FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
- FOR OFF[CIAL USE ONLY
approximately 10 dB less than the effectivP cross-section of aLuneberg reflectox
with dimensions equal to it (curves 2 and 3). This is explained by the presence
of spherical aberration in such reflectors in both the horizontal and vertical
planes. Removal of the internal ring leads to an additional reduction in the
effective r.adar cross-section by 5 dB.
Hollow helispheres, just as Luneberg lenses of various designs can find widesc~le
- applications as decoy targets for antiradar camouf lage, primarily air and space
- objects. Such reflectors have also been praposed for installation on targets and
on controlled decoy targets to increase their effective radar cross-sections.
5. Passive Antenna Arrays
A passive antenna array (a Van-Atta ~eflecto~) takes the form of a device consist-
- ing of several horizontal and vertical rows of half-wave dipoles, positioned ir.
- one plane at a spacing of a/4 from the reflecting screen (the reflector). A metal
plate serves as the reflector. In this case, the dipole pairs which are arranged
in mirror fashion relative to the center of the screen, are coupled together with
coaxial cable sections.
6
bem 4_(~D~~,)z Figure 5.25. Values of the effective radar
-
_ cross-sections of lens re�lec-
' ~ ~ 4 S t.ors, referenced to the effec-
tive cross-section cf a metal
~ 2o sphere of the same ~iameter.
, Key: 1. Circular disk;
I 0 2. Luneberg reflector;
I 3. Helisphere with a ring on the
' ~ 0 ~o ~00 rooo inside ;
~ ,Q uaMCmp. .1.
, 4, Hollow helisphere (linear polar-
~~i ization) ;
5. Hollow helisphere (circular
; 0 ~ 0 ~ � >2 polarizatian) .
, 4~ a ~f 13 1S
I 07 Qd !Q Q � Q The system used for connecting the 18~pairs
~ of radiators by means of cable of the same
r~ i6 Q Q Q length is shown in ~"igure 5.26. The coupled
~ ~3 Q O~ elements (indicated by identical numbers are
located in diagonally opposite quadrants of
~z n to 1~ ~ t(~ the plane of the array. When the electrical
- length of the lines connecting the radiators
whir_h are coupled in pairs is equal, the re-
Figure 5.26. Schematic showing radiated wave front matches the incident wave
the connectian o� frant. In other words, the back-scattering
radiators in a plane of the electromagnetic energy by such a re-
� antenna array. flector occurs in the directicn of the trans-
mitti?ig source.
-97-
_ ~ FOR OFF[CIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/42/09: CIA-RDP82-40854R040400070041-5
FOR OFFICIAL USE ONLY
Antenna arrays have the following major advantages over the reflectors treated
- ear;ier. 1) They have a wider return ~?attern as compared to corner reflectors.
2) '~hey make it possible to modulate the reflected signal in accordance with any
modulating law; 3) They can -return the incident wave in directions other than the
direction to the transmitter; 4) They provide for the selection of the requisite
return polarization; 5) They make it possible to use signal amplifiers built into
the connecting lines, by means of which one can obtain a significant boost in the
effectzve radar cross-sectian of the reflector; 6) They open up the widescale pos-
sibility of fabricating high efficiency reflectorS (false targets) using printed
circuits and stripline technology.
- The effective back-scatter cross-section of a passive plane antenna array is
determined fram the formula:
O~11~
o-
4a '
where G= 4nSe/a2 is the directional gain of the array.
From this:
6 = SeG,
where Se is the effective geometric cross-section (aperture area) of the array.
The effective radar cross-section of an array composed of n half-wave dipoles,
positioned at a spacing of a/2 from each other and at a distance of J~/4 fram the
screen, is equal to:
4aS~ ~ ~
a - ~ (sin ( 2 cos Ol~ ,
~ ~ ~
where @ is the angle of incidence; the factor sin([n/2]cos6) characterizes the
' dipole directional pattern in the plane of the ma~netic field, taking the mirror
- image into account; Se = na2/4 is the a~erture area of the antenna.
The effective radar cross-section of an array will depend on the angle of incidence
of the incoming elactromagnetic wave, i.e., the back-scattering of a Van-Atta
reflector is a of a~irectional naCure. The return pattern of an antenna array of
16 coaxial dipoles in a plane perpendicular to the axes of the dipoles are shown
in Figure ~.27. The return pattern of a flat screen is also shown for comparison
in the same graph. The studies were carried out at a frequency of 2,850 MHz. It
can be seen from the f;gure that in the case of normal incidence of the wave, the
effective radar cross-section of the array is equal to the cross-section of a
flat metal plate (shield) of the same size as the array, while in the case of.
incidence angles of +35� and +55�, it is 3 and 10 dB less than the maximum value.
When a corner reflector is irradiated in a direction which deviates from the opti-
- mal by +20 to +30 degrees, its effective radar cross-section is reduced by 8 to
-98-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/49: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
10 dB; the conclusion can be drawn from this that with identical maximum values of
the effective radar cross-section, an antenna array has a wider return pattern
than a corner reflector. .
a,a6 dB
o_ Figure 5.27. Pattern of the return of an antenna
, array of 16 dipoles in a plane
~p ~ ` perpendicular ~,o their axis.
~ 2 ~ Rey: 1. Metal plane;
2. Antenna array (experimental
2o data) ;
~ 3. Antenna array (calculated
Jp ~ _ data) .
~ ~
~
~o
yp 'p ,76 0 J6 7? 90 B'
d, dt
Figure 5.28. A dielectric rod reflector (the
l shaded portion is covered with
conducti.ve material) .
c, ae
, f6
~Z Figure 5.29. The gain of a dielectric antenna
as a function of its length.
' 8 �
~I
1 1 J 4~ S, 6 G/~
j The major drawbacks to antenna arrays (as passive reflectors). composed of identi-
~ cal half-wave dipoles, is the narrow bandwidth and polarization selectivity. To
~ eliminate these deficiencies, wideband radiators with circular polarization can be
I used as the radiating elements, for example, plane and conical spirals or dielec-
i tric rods.
Abroad it is recommended that dielectric rods by used as the main re-radiating
elements of Van-Atta reflectors. Usually, a dielectric rod has a circular cross-
section over its entire length, decreasing towards one of the ends. At the wide
end of the rod, a volumetric.resonator is cre~ted by means of coating the dielec-
tric wi[h a thin of copper. 'I'he length of the metallized portion is governed
by structural design considerations.
The optimum values of the diameters of a cone shaped dielectric rod (Figure 5.28)
depend on the radar wavelength as well as on the dielectric permittivity of the
material from which the rod is fa'~ricated:
-99-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAL USE QNLY
, d, = O,~r,4z ~~e - 1, .
d~ = j10,~4ci,.
For a polystyrene rod (E = 2.55), at a wavelength of a= 3 cm, dl = 12 ~m, while
for the 6 cm band, dl = 25 When operating at comparatively low frequencies,
it is expedient to use a material with a high dielectric permittivity, for example,
low loss ceramics.
The effective radar cross-section of a dielectric rod is governed by the dielectric
antenna gain, G, which is a function of the rod length:
Q = G2a2/4rr.
The function G= f(Z/~) is plotted in Figure 5.29. Knowing G and the requisite
value of the effective radar cross-section, the rod length Z can be deteYmined
from this graph.
The effective bandwidth of a rod ref lector is approximately +15% (with this fre-
quency deviation frcm the center value, the effective radar cross-section of the
reflector is cut in half).
E, as E , dB
- o
Figure 5.30. Patterns of the secondary emission
~o f of a dielectriG rod (1) and an
1 equivalent disk 63.5 mm in diameter
pp (2) recorded in the 3 cm band.
Jo
.?6 24 1 0 12 ?4 36 9�
~fi '~~Tr
It follows from a comparison of the results of ineasuring the effective back-
scatter cross-sections of a dielectric rod with a gain of 16 dB and a f lat disk
equivalent to it (Figure 5.30), that the main labe of the secondary emission
- pattern of the rod is cons.iderably widCr than that of the disk, and can be brought
up to about 90 degrees, if the gain of the rod is substantially reduced. Naturally,
by connecting several dielectric rod s in an antenna ~~.rray, a fa1.se target can be
obtained using them which has a broad secondary emission pattern and a large effec-
tive radar cross-section.
An extremely simple two-element array can be obtained by means of connecting two
U-shaped rod,s with a bracket. It has been de.m~onstrated that the increase in the
- 100 -
3
FOR .OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFIC[AL USE ONLY
intensity of the return and the width of ~the secondary emission directional pattern
will depend on the spacing between the axes of rods. Thus, with a spacing between
the rods of 2.Sa, a ret~m gain of 6 dB can be achieved above the gain of a single
rod (with the identical directional pattern width).
~ E E,ee dB
E E, ee dB ~
~ o
- , .
~ ' . , ,o ~
ro ~ ~
~ i
I~ / ZO ~
30 4- -
t- - ~ 7~ 1-
^ I I
, ~ I ~ r
J6 24 /7 0 11 2~ JO 9' 1~
-
J6 24 0 ~2 zo 16 9'
. , a) ~ ' Q)
- Figure 5.31. Secondary eu~ission patterns for a U-shaped reflector
with a spacing of 2.5a (a) and a(b) between the
axes of the rods; (the direcConal patterns of a single
rod are shown with the dashed lines).
! If the spacing between the rods is equal to the
f. ~ wavelength a, then the advantage gained in the
gain with respect to a single rod will amount to
. ~~_~1 ` only 3 dB in all, but in this case, the width of
~ 1}. the m~fn lobe is almost doubled (Figure 5.31).
; -
1 The combination of the two U-shaped sections,
~ ~ arrange~ at right angles to each other, takes the
: f orm of a f our-element antenna array (Figure 5. 32) .
For it, the intensity of the return increases by
12 dB as campared to the dual element array. Other
. combinations of U-shaped reflectors are possible
~ whiah allow for even greater return intensity.
~ As studies have demonstrated, the ref lective prop-
Figure 5.32. A f our-element erties of a single dielctric rod are ind~pendent
of the type of incident wave polarization. However,
antenna array. U-shaped reflectors provide for 2 maximum return
_ only in the case where the polarization plane of
the incident wave is normal to the plane of the bend of the reflector. If the pol-
arization plane of the indicent wave is parallel to the plane of the bend, then
-101-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/49: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
the effective radar cross-section is somewhat reduced, where the amount of this
reduction depends on the spacing between the axes of the rods. With a spacing
between the rods of 2.5a, this reduction is approximately 0.5 dB. Thus, when
the reflector is irradiated with a circularly polarized wave, the ref lected signal
will be elliptically polarized and have the same direction as the incident wave.
Elementary reflectors (dipoles and rods) can be joined together not only in planar,
but also in linear phased arrays in an appropriate manner.
The secondary emission pattern of a linear `Jan-Atta array of n radiators is
determined by the expression:
sinrn~ I slnB-F- 2~ Il':
F (0~ = I \ / 1
s~~~ ~ (sin 9 1n(!
\
where d is the spacing between the radiators;
~ is the phase shift between adjacent radiators.
A circular antenna array is shown in Figure
l 5.33. Here, diametrically opposite radiators
~ ~ are coupled together in pairs. For such a
~ Q~ reflector, the expression for the secondary
emission pattern has the form:
F(g)-,l,(-~~~`-sin 2~,
~ ~ ~
~ ~
~ i where Jp is a zero order Bessel function;
~ ~ r is the radius of the array.
j ~ i
- ? s ~ -
The directional pattern of a circular array
2a in diameter and a linear array with a
Figure 5.33. Schematic af a length of 2a are shown in Figure 5.34 for
- circular antenna comparison.
array (1 are delay
lines). The requirement that the return fram the
camouf laged object and the return f rom the
- decoy target simulating this object be identical can be most completely met by
means of Van-Atta reflectors (see �1, Chapter 5).
T'nus, if ~hase shifters which are controlled by a specified program are inserted
in the lines connecting the coupled elements of a passive anteima array, one can
produce amplitu::e modulation of the reflected signal at the requisite frequency.
Let a plane electramagnetic wave impinge on a U-shaped array at an angle of 9,
where the array is made of two radiators positioned at a spacing of 2d from
~ each other and joined together by a feeder of length Z.
-102-
FOR OFFICiAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007142/09: CIA-RDP82-40854R040400070041-5
FOR OFFICIAL USE ONLY
f(e) ' ~
~,o
o�s Figure 5.34. The secondary emission patterns
q6 of a linear array with a length of
ak 1 2a (curve 1) and a circular array
01 _ with a dimater of 2~ (curve 2).
~ 90 ~TO 150 B�
- -O,P ~
-0, 4
I� a phase shifter is inserted in the cannecting feed line which pravides for a
phase shift of e'.JB , then the amplitude of the return expressed as a function of
the incident angle 8 will have the following form [16]:
E= cos 2 k~ 1 cos (kd sin 0).
J
By changing the quantity B (when kZ = const.), one can vary the amplitude of the
return field in a specified direction from the maximum value to zsro. A similar,
result can also be obtained for a multielement array.
The use of amplifiers for the reflected signal designed around tunnel diodes or para-
metric amplifiers opens up broad possibilities for imprwing the design specifica-
tions of decoy targets. Such amplifiers not only make it possible to increase the
effective radar cross-section of an antenna array by several times without increas-
, ing its dimensions, but also to produce a return with specified amplitude, phase or
I frequency modulation. Both one-way and two-way amplifiers can be inserted in the.
~ lines connecting the pairs of coupled elements. In the case of two-way amplifiers,
~ strong feedback can occur bet~een the elements of the array, something which limits
; the level of the reflected signal gain. As a result of this phenomenon, a tunnel
~ dicde circuit makes iz possible to obtain a permissible gain not exceeding 15 to
~I 20 dB.
I
I '
I
Figure 5.35.
~ Schematic showing the connection of
' radiators in a semiact~ve antenna array
with polarization decoupling between the
receiving and transmitting subarrays.
- A structural design with two individual subarrays for reception and retum is used
to increase the decoupling between the radiating elements of a Van-Atta reflector.
The su.barrays are made f rom orthogonally polarized radiators arranged in checker-
board fashion and connected by a feeder, as shown in Figure 5.35. In this case,
one-way amplifiers are emplayed. For the structure shown in Figure 5.35, one can
achieve an isolation between the receiving and ad~acent radiators of more than
50 dB.
-103-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/49: CIA-RDP82-00850R040400070041-5
FOR OFFICIAL USE ONLY
f 2
If frequency conversion such as shown
in the circuit of Figure 5.36 is
employed in the amplifiers built
3 into the antenna arrays, then the
~ f0 f~{dr reflected signal can be phase and
�f frequency modulated. Here, a local
Figure 5.36. Scematic showing frequency oscillator is used for the modulation.
modulation in an antenna array ~e results of tests of a model of
with amplification of the re- such equipment are cited in the
flected signal. "
foreign press [16]. Tunnel diode
Key: 1. lteceiving elements; amplif iers and mixers were used in
- 2. Transmitting elements; the circuit. Mutually orthogonal
3. Mixer; dipoles, arranged an a rEf lecting
4. Amplif ier. screen in checkerboard order played
the part of the radiators. The
frequencies of the received (2,000
MHz) and transmitted (2,150 MHz) signals differed by 150 MHz with an amplifier
passband of 120 MHz. The local oscillator made it possible to employ frequency
and pulse modulation. The measured gain of the array amplifier was 14 dB. Such
an antenna array can be used to simultaneously retransmit several signals at dif -
ferent frequencies, incoming from different directions.
6. Guided Missiles - Decoy Targets
Special guided missile decoy targets are used to simulate air objects which have
a high flight speed. As a rule, they are small aircraf t, launched fram bambers
or missible carriers at a distance from the enemy radars greater than the detec-
tion ran~e for the bomber or rocket carrier. This leads to f alse conclusions
concerning the nature of the attack (instead of the real target, the enemy begins
to pL3rsue the missile), and also overloads the enemy data retrieval and processing
system.
Corner reflectors, Luneberg lenses or other devices which increase the effective
back-scatter cross-section of the missile can be installed on decoy missiles.
However, it is difficult to generate radar returns co~ensurate in power with the
returns from actual air targets by means of decoy missiles equipped only with
passive reflectors.
It is well known that corner and lens radar reflectors produce a good effect in
the case where the wavelength of the radar irradiating them is much less than the
dimensions of the ref lector, while the transmitter and receiver of the xadar are
located at a single point. When the transmitter and re~eiver are spaced a certain
angle apart relative to the ref lector, the effectiveness of the reflector falls
off sharply with an increase in this angle. This is explained by the directional
nature of the back-scattering pattern of such reflectors.
If the signal ref lected f rom a f alse target is small f or t~e simulation of a
, large object, it is necessary to amplify it. For this, a special amplifier is
-104-
FOR OF~rICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-04850R000400070041-5
FOR OFFICIAL USE ONLY
installed in the decoy missile which retransmits the echo signal impinging on the
decoy target. A missile equipped with such an amplif ier-transponder will simulate
a large aircraf t, even with a significant separation angle (relative to the target)
between the r.adar transmitter and receiver. The devices takes the form of a radar
transponder, similar to a conventia~ial radar beacon. In receiving the signals from
the radar, it amplifies them by means of a klystron or traveling wave tube (TWT)
- amplif ier and retransmits them in the dir~ction of reception. The frequency of
the retum signal for a stationarq target will always be equal to the frequency of
the transmitting radar. If the trap simula~tes a moving target, then the freq~sency
of the signal transmitted by it will have precisely the same doppler frequen~y
shif t as in the case of the mo~icin of the actual ob j ect . When it is necessary to
simulate a f alse signal of the same power as the signal return fram a camouflaged
target, it must be consi.dered that the average pulse power of the transpQ'~der
signal of the decoy target depends on the average effective radar CZ05S-section of
the object being simulated. On the other hand, the average return pawer is
governed by the average incident power of the search radar and the transponder
gain. Naturally, the transponder gain of the decoy target should be equivalent to
the effective radar cross-sectian of the object being camouf laged. The following
expression can be derived from the basic radar equation for tl~e gain nf a decoy
- target with an active retum:
K ~ 10 log(4nQt/a2GrecGtrans~' dB'
~
I
; It follows from this that the gain of a decoy target transpor~der is governed by
~ the effzctive radar cross-section of the object being camouf laged, Qt, the wave-
~ length of the radar, a, as well as the directional gain of tt~e transponder antennas
' (~rec~ Gtrans~� It is apparent that the average pulse power of the decoy target
' signal is proportional to the pow~r of the transmitting radar; the nature of this
, power as a function of range should be the same as for the actual target.
The intensity of the returns from actual objects is always subject to considerable
fl~uctuations, which have a definite spectral conposition and corresponding proba-
bility distribution of the signal parameters with time. In order that the retiurns
from a decoy target do not differ from the returns of the objects being simulated
in terms of the nature of the fluctuations, the signal is modulated simultazeeously
with the amplif ication of the signal in the transponder circuitry. The envelope
of the actual signal reflected by the corresponding simulated object is used as the
_ modulating voltage.
Klystron amplif iers are comparatively narrow band devices: electronic frequency
tuning of a klystron is possible in a range of 30 to 60 Mliz, while the bandwidth
of an oscillator or amplif ier using a klystron is only 10 MHz. For this reason, a
klystron amplifier-transponder, installed in a decoy missile, can simulate the
target only for one particular radar or a group of radars operating in one fre-
quency band.
-105-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007142/09: CIA-RDP82-40854R040400070041-5
FOR O~EICIAL USE ONLY
Under actual conditians, several radars can work on an aircraft, bomber or Wherele
~�ehicle simultaneously (detection, tar~et acqusition, fire control, etc.),
each of th~ radars has its own working wavelength. The targst being camoulfaged
can be simuiated ~imultaneously for several radars by mean~ of a decoy missile, on
board which a'~1T -~Ptheiusual kZystrondandscan operatelinea wide10rangeofO~fre00
times more gain tha
quencies.
The American company of "Temco" has designed a TSJT amplif.ier, ~~rhich together with
the power supply weighs 4.5 kg. The equipment is built with semiconductor devices
and contained in a hermetically sealed housing. The antennas are chosen in accord-
ance with the structure of the false target for which the device is intended. The
power used by the amplifier at a DC supply voltage of 24 to 29 volts does not
exceed 80 watts. The service life of the amplifier is 400,hours. When such an
amplifier installed in a light pleasure aircraft was tested, the signals reradiated
by it produced the same blips on the screens of radars as heavypf oyr-engine bombers.
Similar equipment is being manufactured by another American com an Lockheed
Electronics. The equipment complement includes a'TWT amplifier, a Cransistorized
- power supply and matched receiving~and transmitting antennas. The frequency range
is 5,000 to 11,000 MHz. The effective back-scatter cross-section o.f the simulated
- target is adjuste.d by an attenuator at the antenna output and can be increased up
to 850 m2. The minimum output pewer is one watt, although over the majority of the
range it reaches 3 watts. The signal gain varies in a range of 65 to 72 dB; the
- DC power consumptannbesuse3 attaStemper3turerofuf rom V54ttoe+71 ?C and2atValtitudes
The transponder c
up to 21 km.
We shall cite the data on. the American
decoy missile, the GAM-72 "Green Quail"
~ ~ - (Figure 5.37), as an example of decoy
targets on which such transponders and
amplifiers can be installed. This is a
guided missile of the "air to ground"
class. The basic function of the missile
is to decoy the radars of the enemy air
~ def ense system to itself, thereby providing
the long range bombers or missiles with
nuclear warheads the opportunity to reach
~ tr.e set targets uninipeded. In its exter-
Figure 5.37. The "Green Quail" decoy nal appearance, the missile takes the form
- target. of a small aircraft, manufactured from
armor plate, with a short fuselage and
triangular wings. The length of the
missile is about 4 m, the weight about 540 kg and the wingspan'is 1.6'msomethinis-
sile has one jet engine which can deeed~closehto thatf ofpsound.lOThegrange of the
which provides the missile w ith a sp
"Green Quail" missile is 360 lan and its ceiling is 15,000 m. The missile is con-
trolled by an autopilot with program i~n~s�destroyedabi~means ofta~selff destruction
the execution of the comtat mission, v y
device. Special electronic equipment (of the type of amplifier-transponders
-106-
FOR OFFICIAL LSE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/49: CIA-RDP82-00850R040400070041-5
FOR OF'FICIAL USE ONLY
considered above) is installed in the nose~of the missile, where this equipment
makes it possible to produce retums of the same levels as those from a B-52G
bamber on the screens of enemy radars.
The B-52G strategic bomber of the U.S. Air Force, besides the major armaments,
carries f our "Green Decoys" on board. It sfiould be noted, that other means of
antirad ar camouflage are pro~ ided on the B-52G bomber besides the decoy missiles.
The "Green Quail" missile can be launched from any startegic bomber in the U.S.
Air Force. IJhen the missile is hung in the bomb compartment, its wings are folded
and brought to the normal p.ositian i~ediately prior to releasi.ng the missile
from the aircraft.
The guided "Firebee-20" decoy, which can be launched f rom aircraft and ground
- installations, was developed by the American company "Ryan". The length of the
"Firebee" missile is 7 m, the wingspan is 3.9 m and the maximum f light weight is
990 kg. The flight vel~ocity is close to the speed of sound and the ceiling is
23 km. A Luneberg lens is installed in the tail portion af the missile while a
T.WT amplifier-transponder is mounted in the nose compartment. These devices make
it possibel to produce a return Ievel fram the missile comparable to the return
fran an aircraft.
Besides air decoys, it is~ also proposed that ground and water decoy targets be
used, which take the f orm of high power electramagnetic wave retransmission or
reflection saurces. Such decoys, which are set up at a certain distance from the
, objects being protected, by reradiating or reflecting the electramagnetic energy
will attract the guided missiles with the radar haming warheads to themselves.
; It is thought that the widescale application of.semi-active antenna arrays using
i tunnel diodes or parametric amplifiers as the amplifying elements will open up
~ great prospects for the design of decoy targets. Using such devices, one can
achieve the most complete matching of zhe parameters of the signal reflected from
, the real target and the signal fram the simulator.
I~ The effectiveness of all of the decoy targets treated in this chapter increases
~ sharply if a set of ineasurs is implemented for the object they are si.mulating to
; reduce its radar visibility.
I
~ 7. Anti-Radar Camouf lage of Ballistic Missiles
Because of the continuous refinement of systems f or the detection and intercep-
tion of air and space attacks, whd.ch have a great range and enormous destructive
power, extensive work is underway abroad to create means which facilitate the
penetration of ballistic missiles through an antimissile defense system (PRO)
[ABM systems]. For this purpose, various counter-measures for ABM systems are
undergoing intense development in the U.S., which are intended for their equipping
the "At las", "Titan" and "Minuteman" ICBM's, the "Polaris" long range ballistic
missile and the "Pershing" intermediate range ballistic missile. According to
data in the American press, about a billion dollars have already been expended f or
the creation of ABM system counter-measures. A signif icant portion of these funds .
is bei.ng spent on the design of antiradar camouf lage.
-107-
_ " FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/02/09: CIA-RDP82-00850R000400470041-5
FOR OFFIC[AL USE ONLY
Figure 5.38. Standard ballistic missile trajec-
tory.
o~,. ~ ~ Key: 1. Launch site;
` + 2. Powered phase;
N=,ao~M 3. Rocket motor separation
? sp0 " phase;
r,~'~ s 4. Central portion of the
.
, 6 trajectory;
5. Maximum deceleration phase
- (50 g) at an altitude of
10 to 20 l~;
6. Target.
We shaTl briefly examine how the means of antiradar camouflage make it difficult
to intercept an ICBM at various points in its tra~ectory (Figure 5.38).
The problam of intercepting a ballistic missile in the general case consists in
preventing iks warhead from exploding in the region of the object being protected.
In the case where a nuclear warhead is used, interception must be made at the
rather high altitude and long range from the protected facility, otherwise, the
exp'osion of such a device nauses destruction over the protected territory.
Calculatians perf ormed in the U.S. siiow that an interceptor should be launched
approximatelq 15 seconds after receiving the intercept cammand. The character-
istics of existing engines and power sources, as well as the comparatively long
time needed to cage gyroscopes make it very difficult to meet this requirement [24~.
It follows from this that for the timely interception of an ICBM, it must be
detected at the greatest possible range.
The utilization of tools which reduce the power of radar returns form ICBM's
makes it possible~ to sharply reduce the range and detection probabiJ.ity of the
missile by a radar. If the effective radar cross-section of a ballistic missile
warhead is reduced by a factor of 20 using poorly reflecting forms and antiradar
- coatings, then as follows from for~ula (2.1), its radar detection range is more
than cut in half. The target detection probability is reduced b y no less than the
same factor.
In this case, very little time remains for th~ interception of the ICBM. Reliable
target interception can be accomplished only with a sharp increase in the speed of
the interceptor.
The relationship between the velocity of the interceptor vm~ and the target
detection range D for a protected zane radius of 185 km is shown in Figure 5.39.
It can be seen fram the graph that when the ultimate detectian range of an ICBM is
cut in half (the effective radar cross-section is reduced by a factor of 16), the
-108-
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400074441-5
FOR OFFICIAL USE ONLY
missile can be successfully intercepted on in the case where the speed of the
interceptor is increased by approximately a f actor of 1.5 times. When this condi-
tion is not met, the nuclear warhead will then explode over the ter;.itory being
defended.
- It is obvious that it is desirable
to achieve a reduction in the effec-
~max. w~Ce' tive back-scatter cro~s-section of
m/sec a ballistic missile over all portions
as0o of its trajectory. However, in this
~ case it must be kept in mind that
~ 1 3 depsite the relatively simple geo-
' metric shape of the component struc-
100o tures of the missile, the value of
its effective radar cross-sectYon
will change in different portions of
~s0o_ the f light . This is due to the
J70 7v0 f1f0 1a80 D, ~M
_ sequential separation of the rocket
stages and the continuous change in
FigurE 5.39. Interceptor speed as a func- the radius of the last stage (the
tion of target detection warhead) relative to the radar
range. station. Morevoer, the effective
Key� 1. Target velocity of radar cross-section can change
- vt = 6,000 m/sec; because of back-scattering of the
radio waves by the rocket engine
2, vt = 9,000 m/sec; flare, as well as because of inhomo-
~ 3. vt = 12,000 m/sec.
geneities in the ionosphere, per-
~ turbed by the operating engine.
~ Despite the fact that the missile
; is the most vulnerable in the powered phase of the trajectory, there is little
i probability of its detection in this phase by means of ground radar since in this
' case, their range will be limited by the curvature of the ear.th. The placement of
long range missile acquisition and tracking radars on radar petrol aircraft for
satellites as yet still involves considerable technical difficulties.
~ Having achieved the specif ied trajectory parameters, the rocket begins the middle
phase of the f light outside the limits of the atmosphere with the engine shut
dawn. In this phase of the flight, the warhead can be separated fram the body of
the rocket. The.detection range and probability for a warhead in the central
phase of a tra jectory can be significantly decreased by means of special measures
to decrease its effective radar cross-section, which reduce to the selection of
the optimum shape of the rocket nose cone and the utilization of radio absarbent
materials. In order that the sharp point of the warhead be directed towards the
radar station of the air denfense system at all times, for the purpose of main-
taining the minimum effective radar cross-section of the warhead durings its
flight, it is necessary to stabilize the nose portion of the rocket over its
flight path. The need f or stabilizing gear arose because of the fact that the
nose sections of missile which were not oriented towards the radar (for example,
the "Mark-4" on the Atlas-8, Atlas-F and Titan-1 ICBM's) turn end over end in the
- 109 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/42/09: CIA-RDP82-40854R040400070041-5
FOR OFFICIAL USE OiVi,Y
central portion of the flight trajectory and represent large targets for the opera-
tors of enemy radars.
Various decoys can be used following the detection of the nose of the rocket to
camouf lage it, i.e., to disorient the enem~ or completely saturate the carrying
capacity of the detectian and tracking system of the air defense complex.
- The effectiveness of antiradar camouflage of ICBM's using decoy targets can be
quite high in the central portion of a tra~ectory. Since the influence of the
atmosphere is completely eliminated in thise phase of the flight, light objects
can be used as the decoy targets, f or example, such as dipole ref lectors or in-
flated balloons having the shape of the warhead or a sphere.
For example, successful tests in the U.S. of a set of such decoy targets ejected
fram a Titan long range ballistic missile were reported in the press. The rocket
which was equipped with dummy nuclear charge flew 8,000 km and fell in the region
of the south Atlantic Ocean.
After separating the spent stages, the missile warhead jettisoned six decoy
targets. All of the decoys had balloons in the noses, where these balloons pro-
duced magnif ied b lips on radar screens which camouflaged the true dimensions and
position of the target and made radar observation diff icult [7].
Following the ejection of decoys from the nose section of a missile, it is neces-
sary to correct the position of its center of gravity which is shifted as a result
of dumping the decoy targets.
Lisorienting decoys can also be placed in the last stage of the rocket, and in this
case, following the ejection of the decoy target and the separation of the last
stage, it should be thrown off to the side from the warhead by means of braking
motors or destroyed so that the trajectory of the missile warhead cannot be gov-
erned by the flight trajectory of the last stage.
Despite the f act that at f irst glance the destruction of an ICBM in the middle
phase of the trajectory is the most advantageous, since it can be accomplished at
a great distance from the def ended facility, the prob lem of guiding the inter-
cptor where decoy targets are used becomes so complex, that in the opinion of
foreign specialists, there is little probab ility of an interception in this case
and such an approach can be treated only as an auxiliary one.
The use of antiradar camouf lage which reduces the eff ective back-scatter cross-
section of an ICBM takes on especially great significance in the final flight
phase of the missile. In this phase, the use of f alse radar target "decoys" can
be less effective than during other phases of the trajectory, since because of
' the different dynamic conditions f or the entry of the warhead and ~alse targets
into the atmosphere, the probability of selecting the warhead from among the decoys
increases. The warhead, which has greater weight and lower frontal resistance
begins to lose velocity at comparatively lower altitudes, while for metallized
strip or inf lated balloon type decoy targets, the reduction in speed becomes percep-
tible early on at high altitudes.
- 110 -
FOR OFFICIAL USE ONLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5
FOR OFFICIAI. USE ONLY
s y e
s
~ ~
_ s ss!ni;Me�.~~~.rNr: , ,,,:,:;~...a..
' e `r ~ ~ 9 -
ti
; ~
o ~ i !0
~ j 1
J ~
? ~ 1
f
~
Figure 5.40. The use of antiradar camouflage in various phases of the
f light trajectory (x, y, z) of a ballistic missile.
Key : 1. Powered phase of the trajectories;
2. Point of separation of the last stage;
I 3. Destruction of the spent stage or the change in its
I
tra3ectory;
4. Passive ja~ing or decoy targets;
5. Central portion of the trajectory;
6. False targets in the f orm of air balloons;
7. The regian of entry into the dense layers of the
atmosphere;
8. Heavy reflectnrs (decoy targets);
9. The poin~ of tra~ectorq change;
10. Maneuvering nose cone;
~ 11. Missiles guided to the radars;
12. Target.
~
~ ~
i
~ The recognition of warheads when they enter the atmosphere can be made consider-
ably more difficult if heavy objects are used as the false targets, the ballistic
coeffients of which are equal to or close to the ballistic coefficients of the
warhead.
The designers of false targets have been forced to increasingly deal with the
refinement of air defense radars as regards the increase in the volume of inf orma-
tion which can be extracted on air targets (their dimensions, f luctuations in the
return, objects rotating end over end in space, etc.) by means of new techniques
of analyzing the fine structure of the retu~zn. This in turn f~orces designers to
make the structure of decoy targets increasingly complex, something which leads to
-111-
~ FOR OFFIC[AL USE O1VLY
APPROVED FOR RELEASE: 2007/02/09: CIA-RDP82-00850R000400070041-5

APPROVED FOR RELEASE: 2407/02109: CIA-RDP82-00854R000400070041-5
FOR OFFI~IAL USE ONLY
an increase in their overall dimensions and weight. However, with an increase in
the weight of decoy targets, it is necessary to ccnsider the fact that each kilo-
gram of payload costs the same to deliver, regardl2ss of the dest-uctive power of
the charge. In other words, increasing the weight of decoy targets unavoidably
leads to a reduction in the weight of the missile payload.
A missil~ warhead, entering the dense layers of the atmosphere in the descending
phase o� the f light trajectory at supersonic speed, fo