JPRS ID: 9883 USSR REPORT ELECTRONICS AND ELECTRICAL ENGINEERING

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• Content Type: REPORTS

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JPRS L/9883
31 July 1981
USSR Re ort
p
ELECTRONICS AND ELECTRICAL ENGINEERII~G
CFOUO 8/81)
FBIS FOREICN BROADCAS~' INFORMA`TION SERVI~E
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JPR5 L/9883
31 July 1981
� USSR REPORT ~
ELECTRO~VICS AND ELECTRICAL ENGINEERING
(FOUO 8/81)
CONTcNTS
ANTENNAS
Effect of Cylindrical Screens on the Noise Temperature of
~ Mirror Antennas 1
Multichannel Light Modulators for Optical Signal Processing
- Systems of.Antenna Arrays 5
~ CO1~fMUNICATIONS, COMMUNICATION EQUIPMENT, RECEIVERS AND TRANSMITTERS~
NETWORKS, RAD~O PHYSICS, DATA TRANSMISSION AND PROCESSING,
, INFORMATION THEORY
Determining Probability of Intermodulatory Interference in a
Receiver 17
PUBLICATIONS
Analog-Digital Converters (Designing Electronic Equipment
Using Integrated Microcircuits) 23
ATS jAutomatic Telephone Exchange] Software 27
Gas-Discharge Matrix Displaq Panels 32
Parauietric Reliability of Hydroacoustic Antennas 35
Radar Methods of Earth Studies 39
Radiocommunication Channels for ASU TP 42
Radio Communication Equipment of Airports 43
Reliabiliry and Testing of Radio Parts and Components 45
- a- [III - USSR - 21E S&T FOUO]
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Statistical Analysis of Multiple-Level Pulse Trains 51
Transmission or Digital Information Via Low Speed Channels
of Communication 54
b ~
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ANTENNAS
EFFECT OF C`ILINDRICAL SCREENS ON THE r10ISE TEMPERATURE OF MIRROR ANTENNAS
Moscow RADIOTEKHNIKA in Russian No 2, Feb 81 (manuscript received after
completion 28 Jan 80) pp 74-76
[Article by A. M. Somov]
[Text] When highly dirzctional antennas with low-noise receivers are used,
it is very important to reduce the noise temperature, an integral parameter
which is a function of the directional properties of the antenna and the
efLective noise temperature of the environment [1].
To reduce noise temperature of antennas, it is necessary to attenuate the
level of extraneous emission. We k:.ow [2] that an effective measure to reduce
extraneous emission of mirror antennas is to install cylindrical screens around
the perimeter of the antenna aperture (Figure 1).
The methods of calculation of antennas with such screens have been elaborated
in sufficient detail. For this purpose, a method of geometric diffraction
theory (GTD) is used which considers both the change in the field distribution
in the aperture resulting from the presence of the screen as well as the pre-
sence of rapid oscillations in the ~ield at the edge of'-the screen [3].
Figures 2 and 3 show the beam patterna (DN) of a mirror antenna with focal
length F= 45.7 centimeters and aperture diameter D~ 122 centimeters,
calculated in the frequency range of 4 GHz in the planes E and H, respectively.
The solid line denotes the antenna beam pattern without the.cylindrical screen;
the dotted line is with a screen 20.3 cm long; the dot and dash line is with
a screen 50.8 cm long.
'ioeg~coF~ _ . . ~o~`co�2~ . _ .
30 '~0
~ >0 10
a _
- !0 ~0
~D . 30 :
F , .0 20 4a 60 BO 1001zD9� . ~~ZO y0 60 ~ 80 IOOLZO B�
' Figure 1 Figure 2 Figure 3
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For these same cases, the relationship was calculated of noise temperature of
an antenna as a function of its inclination toward the horizon. The calculation
was performed on the basis of a standardized portion of power of thermal
noises of each sector of the beam pattern (DN). For example, a standardized
portion of power equal to ~.113 wihtout a screen in the plane H and 0.147
in the plane E; and with a 20.3 cro screen, 0.00~ and 0.019, respectively,
corresponded to a sector per rear hemisphere (90�-120�).
The portion of power of noises received from the rear half-space beyond
this sector is small and does not affect noise temperature. In calculations,
thermal losses of the feeder and thermal emission of the atmosphere reflected
on the earth's surface were ignored.
The surface itself was assumed to be smooth according to Rayleigh; meteoro-
logical conditions corresponded to dry, clear weather.
The relationship of noise temperature (Sh'~) as a function of the angle of
inclination was determined according to the formula
Q s--a . _
~ Q~ T~ E' ~e~ si~ ede + S(T~1 T~,r) E' (6) stn 9d0 S Tse ~ E' (B) sln Bd9 J,
a ~-a
d" ~ .
where GO is antenna gain in the direction of the primary emission maximum;
E2(6) is the beam pattern according to power; a is the angle of inclination
of the antenna to the horizon; Ta = T3/ ~ is the effective noise tem-
0 a a
perature (DShT) of the atmosphere in the sector of angles from 0 to a; Ta is
the brightness noise temperature of the atmosphere in the direction of the zenith;
in this range of frequencies for dry, clear weather equals 2.9�K; p~ arctg
(Ta/T or); T is the brightness noise temperature toward the horizon. Under
the s~me con~~~ions p= 0.028;
ae ~ sin a cos 6-{- p; b, = sin 8 cos a;
T ~T' arct ~a; - b;~ sln (9 -f- a) ,qaA a~ ) b~,
6 Ya~ - b~ g (a. + b.)' sin (B - a)
y~b~ - o~~ sln (9 a) (Qa b~~ 1~51n (9 - a)
d In ~ ~ AnA bi ~ ai
T~' ,Yb;-a; -Y~b~-a~~sfn(6~-a)-}-(a,-Fb.~l~sln(9-a)
is effective noise temperature of the atmosphere in the sector of angles from
a to~r-a.
~
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Effective noise temperature of the smooth surface of the earth respectively
for vertically and horizontally polar~zed thermal emission in the aector angles
from a to n- a is determined by the following expressians:
TbP 4cz~` y~sin'6-sin'a..~ 2~Aa.-Bb.) X
o~-be . - ~us-b~.
a ~ae-bs~5111(6-}-a)
X 2- arctg ~(Q. .t- ba)' sin (e - a) Aa~ v; ~ b~;
~ 4c~y~~ ~e ~~sin' B- sin' a- Aas - Bb. X
a~ - b~ . Y b~ - a~
� .
~'n ~~bs - ae~ s(n (6 a1 la. b.) il sin (9 - a) ~
-1~~b;-aB~ sin (e+a) -f- la. b.) l~sin (9.-Q~ �
4 y~cT~ 2 (A~~ - Bb~)
.T~ - s s~l~sin' 9- sin' a-}- X
~r br l V a~ - b~
A ~a~ - b~~ sln (9 a) ,
X{ 2-. afCtg (ar br~y 810 (9 a~ J~.
while in the sector from ~rr ~ a to ~r
4~ ~cT~ Aa. - Bb, 4 7~T~ Aa~ - Bb~
T~~ ~ Q~ - b~ Y C~ - be ~ T~' a~ - br ~ a~ - b~ .
r r
where T~ is the at~solute physical temperature of the earth's surface; e is
diel~ctric permeability; in this frequancy range for dry soil,:e = 3.5;
a..~ - c sIn a cos C-~- ~c; Q~ sfn a cos B-}- ~c; A-- sin a cosb;
b.- -ccosasin9;. br~�-cosasin6; B- = cosa~in0.
Noise temperature was calculated separately for each plane E and H, wherein
each time was assumed axial symmetry of the beam pattern. The practical dif-
ference of the beam pattern in these planes was considered by averaging the
results of calculation in terms of the main planes. Furthermore, in each of
the planes was considered two cases of polarization of thermal emission:
~err.tcal and horizontal., after which the calculation results were also averaged.
In thi~ way, the calculated noise temperature is valid for an antenna operating
with circular polarization. The relationship of theoretical noise temperature
versus the angle of inclination of the antenna to the horizon ts cited in
Figure 4(solid line: no screen, dotted line: screen 20.3 cm long; dotted
and dashed line screen 50.8 cm Iong).
3
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40 ,
30
20
10 ~ "
D' ZO 40 60 8l! d�.
Figure 4
As the results of analysis showed, cylindrical screens in the aperture of
mirror antennas are effective means for reducing noise temperature.
References
1. Somos, A.M., ELEKTROS~YAZ', 1979 No 3.
2. Ayzenberg, G.Z., Yampol'skiy, V.G., Tereshin, O.N. Antenny UKV [USW
Antennas], Part I, Moscow, "Svyaz 1977.
~ 3. Hwang, Y.M., Han, C.C. IEEE Int. Symp. Dig. Antennas and Propag.
Univ. Md. College Park, Md., N.Y., 1978.
COPYRIGHT: "Radiotekhnika", 1981
8617
CSO: 1860/339
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MULTICIiANNEL LIGHT MODULATORS FOR OPTICAL SIGNAL PROCESSING SYSTEMS OF
ANTENNA ARRAYS
Moscow RADIOTEKHNIKA in Ruasian No 2, Feb 81 (manuacript received 27 May 80)
pp 6-14
[Article by L. D. Bakhrakh, D. B. Ovezov (deceased), S. G. Rudneva and
V. B. Shverin-Kashin]
[Text] Introduction
Optical radio signal processing systems have become very popular in the last
decade. The use of coherent light as an information carrier enables the per-
formance of parallel processing of information and its transmission, with great
speed. These properties of coherent systems govern the outlook for their use
to process the signals of antenna arrays, in order to reaolve such problems
as parallel surveying of space correction of errors due to defornnation of
the profile of mirror antennas (problem of focal synthesis) [2, 3], processing
of signals of circular arrays [4, 5], some problems of antenna measuring tech-
nique [6] and processing of signals in stations which have an artificial aper-
ture [7].
'Phe basic component of any optical processing system is the information input
and light modulator device. There are many different types of modulators, which
may be explained by the large number of physical effects that enable us to
alter amplitude and phase of collimated coherent light flux; and also by the
large number of inedia which can be used to implement certain effects. Various
types of modulators are also used in signal processing systems of antenna ar-
rays. The resolution of some problems requires a system with real-time signal
processing (parallel surveying, focal. synthesis). Thp modulator must perform
operative input of information, thus it employs a medium with lag-free variation
of parameters (coefficient of transmittance, index of refraction, thickness,
etc.). In other cases the signal may be subjected to intermediate recording and
media are employed which have memory (recording on photographic film, thermo-
plastic recording)~ e.~., signal processing in stations having an artificial
aperture, problems of ineasuring technique. In this way, specific requirements
imposed on a data inpu*_ device depend on the nature of the problem being tackled.
In addition to the requirements governed by the specifics of individual problems,
' however, there are general requirements which are basic in natu~e~ that are
' related equally to all modulatore utilized to process antenna array signals.
These requirements will be examined below.
Basic Requirements Imposed on Modulators Used in Antenna Array Signal Processing
Systems
5>.
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A specif ic feature of antenna array signal processing systems is their multi-
channeling. A modulator with a number of channels equal (sometimes more) to N
corresponds to an antenna consisting of N elements. According to the nature of
the problem to be tackled, the number N may vary widely: thus, in the problem
fo focal synthesis the number of channels is comparatively small--as a rule
10-20; in parallel scanning it conatitutes several tens or hundreds; in
artificial aperture systems it may be over a thousand. Naturally problems
may arise linked with the multichanneling in certain instances, as regards
placing a modulator in the aperture of the optical processing device which
is limited in size.
An extremely important aspect of light modulators used for service in antenna
array signal processing systems is the complex nature of distribution of the
SHF field in antenna elements. Signals of individual elements differ in amp-
litude and phase. The light modulator must transmit a complex field from
the antenna to the coherent light flux. The law of amplitude-phase distribution
in light flux passing through a modulator must satisfy the law of field distribu-
tion in the antenna, or else the signal p:ocessing ~ob can not be tackled.
We shall detail this requi~tement here.
If each element of an antenna array separately contained information about the
amplitudas and phases, then the ~roblem could be resolved by direct effect in-
dividiually on light amplitude and phase. It would then be sufficient to set
two layers in the path of the coherent light flux, one of which could alter
the degree of transmittance (affect light amplitude), and the other which
could alter its thickness or coefficient of refraction (affect its phases).
But it is extremely difficult to obtain separate information about amplitudes
and phases of signals in discrete antenna array elements, considering their
lwo directionality values: it would mean solving the signal-to-noise problem
- in each channel. Furthermore, the use of inedia with two variables to modu-
late lighC and solve problems of signal processing of multiple-element antenna
arrays would be inefficient. Transmission of information into light flux about
amplitude-phase distribution of the SHF field in an antenna array is accomplished
by effects on any (according to the material) single parameter of the modulator's
medium. For this purpose, in each processing channel corresponding to an
individual emitter, the signal must be specially processed to obtain control
voltages.
Control voltages can be obtained by linear or non-linear processing of signals
in individual channels of the processor. Linear processing signifies process-
ing where the SHF signal is amplified and sub~ected to frequency transformation.
These transformations are linear in that they retain the amplitude and phase
relationships between the signals of individual channels. A change in the
variable parameter of the modulator medium occurs with the frequency of the
modulating voltage. Let us observe that in linear processing of signals,
frequency transformation is not an essential prerequisite. Indeed, in the.most
developec~ modulators today, the frequency of tt?e control voltages is much
lower than the frequency of signals received by the antenna. A trend has
recently appeared toward increasing the frequency of control voltages up~. to
and including the frequency of the initial signals. According to how the
parameter of the medium is changed, there is moduistion of the phase and ampli-
tude of the light flux passing through the modulator. In this way, in linear
signal processing the transmission of information into the light flux is performed
_ by amplitude or phase time modulation and may, for instance, be effected using
ultrasonic or optoelectronic modulators.
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Let us consider nonlinear preliminary proeessing of signals. In contrast
to linear processing, the control voltage in this case affects the medium
of the modulator and is proportional to the intensity of the radiosignal and the
eignal entering the modulator, but has no frequency change. To preserve information
about the anplj.tude and phase, an external reference field should be used
and thereby obtain an interferogram (hologram) of the field; or a phase detector
used to detect one of the quadrature components~ which is also a holc~gram.
Therefore, in nonlinear preliminary signal processing, information about the
field in the antenna array is transmitted into the light range not with the
_ aid of time modulation, but through ampli~tude and phase distributions.
On the Role of a Three--Dimensional Carrier Frequency
When control voltages of linear preliminary signal pro~essing are obtained, the
light flux is time modulated; in nonlinear processing, amplitude or phase dis-
tributions of the light flux are produced in the modulator. In both cases
one variable parameter of the light flux is utilized. In this context, there
is a certain equivalency of such modulators from the standpoint of inf.ormation ~
possibil3.ties and uniqueness of depicting the SHF field in the light range.
Let us express the field distribution in a linear antenna array whose elements
are situated along axis x by the function
!P (x. t) -Ap (x)sin [mpt ~P (x)J, (1)
where A P(x) and ~P(x) are the distribution of amplitudes and phases of
radiosignals; wP is angular~.�frequency of the radiosignal.
After the appropriate linear preliminary transformations of the signals in
(1) and as a result of amp:Litude modulation at the modulator output, the fol-
lowing light field will be observed
f, c. - sIn rol {1 m, (x) slo [4t ~p (x)1) - sln ~ot ,
+ m'2x~ cos ((m - Q) t - ~o (X)1- "`'~x) cos [(m Q)! -I- 4P (x)1. ~2)
where ma(x) is the index of amplitude modulation proportiona" to the amplitude
of Ap(x) of the signal in the antenna; w is the angular frequency of the collimated
light flux of coherent light; St is the angular frequency of the modulating
voltage.
Light field at the modulator output in phase modulation is expressed in a
similar fashion:
t, - sln {wl m~ (x)sin [41-~ ~p ~x)J) - .1. [my (x)1 s~n ~t - _
- ~ [,?r~ (x)) s~n - Q~ t -~p (x)1 + ~ (m~ (x)] s~n + Q) ~ + ~p (x)].
~ ~3)
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where m~(x) is the index of phase modulation proporti.onal to the amplitude
of the signal in the antenna; Jp(n~ and J;(m~) are Bessel ~unctions of the
zero and first orders.
1, - sin ~ut -1 m 2~x~ sin ((m- gj - 4y ~X)I 1 ~ Z~x~ s~n Q) t + ~p (X)]- (4)
As can be seen from a comparison of (1) and (4), the useful informa.tion is
contained in th~e side frequencies in both cases. The phases of the SHF
signals is reproduced to within the sign in the light fields of the side
frquencies, the amplitudes of the SHF field are transmitted by the
amplitudes of the side frequencies. In phase modulation, amplitude-phase
relationships between the channels are preservpd as long as the index of
phase modulation is small.
In zonlinear preliminary signal processing, the control voltage can be described
by the function
, frpp ~z~ b -F ap sln qP (x), ~5~
where b is the level of the reference signal.
As a result of the impact of control voltages on the amplitude of the light
flux at the modulator output we find that
aP (x) ap (x) _ ,
~e - b stn rot 2 cos [~f - ~P (x)] 2 cos [~t ~y (x)j � (6)
If the control �~ol;.age affects the phase of light, the field is described
by the expression
fa~o - sln (~l a~ (x) sin ~pp (x)] sin (~i) cos [aP (z) sfn ~p {z)j ~
cos (~i) sin (ap (z) sin ~P (x)j ~ [ap (x)) ~ tn ~t -
-.I, [ap (x) ]sln I'nt -~p (`X)J -I- IaP (x)j sln [eut ~P (x)~]. . ,
In equation (7) the constant component of phase, proportional to the level
of the reference signal b, is omitted.. In (6) and (7), as in time modulation,
there are three light fields at the modulator output: the field of the constant
component and two fields containing the SHF signal characteristics. This is
basically due to the facC that any kind of modulated field can not be described
by a si::~le component.
Leaving aside the question of interference due to the constant component of
light flux for a while, let us mention the ambiguity of depiction of the HF
field by light fluxes. This ambisuity is inadmissible ir. a11 problems involved
with the processing of antenna array signals. In problems of paralYel scanning,
owing to the presence of complex-coupled fields, a loss of the sign of angular
coordinate of the source ~ccurs; the same may be said of an artifici~l aperture
station. In focal synthesis problems, the presence of these fields precludes
the possibility,of matched reception. Under these circumstances, system efficiency
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can only be preserved in special cases where there exists additional information
about the sign of the angular coordinate or tl:ere is a guarantee that the
sources are located on the same side of the line normal. The latter condition
is made if the array elements have sufficient directionality and are turned to
ensur~ reception only on the left or only on the right of the line normal.
The above makes it clear that in the averwhelming majority of cases, special
measures must be taken to eliminate noise due to the simultaneous presence
of complex-coupled light fields in the input aperture of the optical device.
The situation can be rescued by three-dimensional filtration of signals,
i.o., by d~flecting fluxes corresponding to these fields. The linear component
r. should be inserted into the independent variable of the phase multiplier
o~ ~he control voltage of (5). Then expressions (6) and (7) will become,
accordingly:
= b s1n wf a� ~x>
f3 ce ~ COS ~lllf - ~P ~X~ - curXj - C8>
. - ap 2x> COS ~wf ~Pp ~z~ ~XX
f4ce ,~o Iap (x)) stn ~t - jaP (z)J stn [~t ~ ~pp (x) - ~Fxl
. (ap (x)J sin [cuf ~pp (x) cnsxj. -
(9)
Fluxes corresponding to the three light fields-at the light modulator output
according to (8) and (9) are now propagated in directions characterized bj? the
angles:
9o~Q'g~=k'B_~~._k ~
where k i.s the wave number. The parameter w may be viewed as a three-dimen-
sional carrier freqency [8]. With an increase in w, separation (filtration)
of the sectors of unique correspondence of light fields and SHF field increases.
Intr~duction of the three-dimensional carrier may 'require au increase in the
numb~r of channels of the modulator as compared to the number of array elements.
The relationship between the period of the three-dimensional carrier and the
number o� variable elements (channels) ofi~the modulator is a function of the
nature of the problem being tackled.
Let us analyze the r~lationship between the period of the three-dimensional
_ carrier freqency TPr and the distance between the modulator channels dm,
assuming that the three-dimensional carrier and the modulator channels are
distributed along the x axis. Based on the principles of nonscalar simulation,
a section in the p~.ane of indication of the optical system (this is usually
the focal plane of the transforming lens) can be determined;:which is situated
along the x~ axis and corresponds to the scanning sector of the antenna array.
In the commonest case the scanning sector is measured through an angle of 90�
with respect to~~the line normal to the array. The sector whi.ch images the
sector in the optical system is determined by the ratio a/d and the focal
m
9 ~
F~R nFFT~raT. TT~F nNr.v
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length of the lens f. This sectQr is periodically
repeated within the wide diffraction spot which corresponds to one channel;
this is the result of nonscalar simulation [9].
In Figure 1, any fragment x~i, x~L ; x�2, x~2 , etc. depicts the antenna
~
scanning sector. The length of this iragment is
a
X~~x~' ~2dm f~ ~1~~
In the absence of a three-dimensional carrier, one diffraction spot J(x )
in the center of each fragment corresponds to the signal entering from ~he
source situated in a direction normal to the antenna: the width of the spot
is controlled by the overall length of the modulator. If the signal from
the source enters at some angle ~ to the line normal, each fragment will
show two diffraction spots J(x ) and J*(x ) in conformity with the presence
of two complex-coupled light f~elds in the~modulator. Both. spots are displaced
(Figure 2) from the center of the fragmenr symmetrically by a distance equal
to
a
nx~ m dm jsln (11)
Let use consider the same modulator with the introduction of a three-dimensional
carrier, assuming that its period
Top ~ dm.
To satisfy this condition, signals being fed into the modulator channels must
first pass through a delay line or phase inverter and acquire additional phase
shifts which are lir.ear functions of the channel number. Now, in conformity
with the steepness of the linear phase incursion, the spot corresponding to
a signal from the source situated in the direction of the line normal, is
displaced in each complex-coupled field (rigure 3) by an amount
~~~6'~) A � dm J , (12)
where denotes the phase change between two adjacent channe].s introduced with
the aid of the phase inverter, delay lines or any other method.
The quantity determine~ the period of the three-dimensional carrier frequency
Tap-~ ~ dm. (13)
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~~X~~
.
-
~
~
~
x~~ 2~f/dm z~t 'r~3 '~~P
scanning~sector
Figure 1
~~(x~1; ~'~fz~)~ _
~
~ Mr ~rX'
~ = ~~X~~ . ,f,~m . .
y~~Xa1 ~',(x~) -
' ~ d x~~~ x~Dt X~p
Figure 2
Each diffraction spot in Figure 3 correaponds to.a signal passing through
the array along a line normal; thus the position of these spots determines the
center of scanning in each of the two light fields. With an inclined incidence
of the signal onto the array, the diffraction spot moves away from the center
of the sector accordingly in some difection through a fragment
~ Is1n~. (14)
It is difficult to show that, for sectors depicting the scanning sector in
two complex-coupled fields not to ove~lap (Figure 4), the size of the phase
jump of signals entering ad~acent channels of the modulator must be limited
to values lying within the limits of 0 to ~r radians. This condition may be
satisfied by an appropriate narrowing and orientation of the beam pattern of
the smitting array at an angle. The direcCion of their zero emission must
satisfy the conditions:
e~ tt _ o~,
sln - kP~~ ; sln W~ - kP D~ ~ ~~5~
where k= 2/ a is the wave number; Da ia the distance between array elements.
P P
Let us note tYeat the separation of sectors in complex-coupled light fields can
be produced without rotating emittera, if their beam patterns are narrowed correct-
ly (Figure 5).
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~~X~) y~~X~l .
.
~ ~~aw~ ` . ~ , f I ox~~a~1
~j . x~ ~ ~ ~ .
o sin ~ sins~ v ~sin~ X~.
Figure 3 .
, ~ ~~X~~ ~~X~ j
Gxm(dv) . ax~f~~1 ` "
~ ~
~
% ~ ~ ~
, / ~0. - ~X~ 0% .
X~
sing~ s~n~pQj 0 -siD~ 0 Sll?~o Sinlp ~
Figure 4
-
~*~x~) , ; _ .
?
' ! ; ~ .
. ~ j - 1~ ,
\
, ~ ~ 0 ~ .D i
.o -sinsa - P ~in~
Figure 5
Thus, it is theoretically possible to separate sections of unique correspon-
dence to the scanning sector in the optical system by introducing a three-di-
mensional carrier with a period of Tpr > dm, with rotation and adequate
narrowing of the beam patterns of C.he array emitters. As illustrated by an
artificial aperture station, it can be shown to be possible to implement this
reception in practice. In stations of side scanning, s3gnal processing involves
the use of a natural phase incursion from "channel" to "channel" due to the
Doppler component. For this purpose, the pattern of the on-board antenna
(i.e., the pattern of the individual emitter) ia appropriately rotated within .
the arr:y. The period of the three-dimensional carrier may be much greafer
than d~ here. The necessary narrowing of the pattern is easy to implement,
since the size of the on-board antenna can be made several times greater
than the distance between elements.
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, .
As concerns other problems: parallel scanning, focal synthesis, processing
signals of circular antenna arrays, practical realization of the require-
ments necessary to separate sectors in an optical system is encumbered by
man} technical problems. The use of a three-dimensional carrier having
a rather large periud (TPr > dm) would require the use of narrow beam patterna
of the emitters A~ 90�. To shape such a pattern the aperture of the in-
dividi~al element would have to be
D,> 1,5).P, (16)
- where ~P is the radiosignal wavel~�ngth. The period of installation of emitters
in contrast to a synthesized antenna should be of the same magnitude Da. In
this connection, a problem of polyvalency arises which results from the presence
of interference lobes in the scanning sector. The array factor and the width
of the pattern of the elements is in a relationship where the unique scanning
can be guaranteed within the sector not to exceed � aresin a ~�20�. In prob-
_P ~
2D
a
lems of focal synthesis and signal processing of circular arrays, the emitter
period should be on the order of ap/2; it is thus impossible to shape the
emitter beam pattern in conformity with requirements [15].
. ~(~p) ~
Q~ - ; .
, ~ . \
i ~
~ ~
i .
- ~
_ ~
0 ~ a ~sin~p
~(~p) ~
bJ ~ ~ ~ ~
i ~ . ~ .
i '
~~`i \~i- .
-!~2 0 >~2 . Su~y~
Figure 6
An Ldeal example of using a three-dimensional carrier having a period exceeding
the interval between c:hannels in a modulator is a tranaparency with the record-
ing of the signals of a s3de scanning atation. In problema of processing
signals of antenna arrays in real time, the uae of such a modulator is limited
to a system of parallel scanning with a sector not to exceed 40�. In this
case the problem can be tackled with the use of an optoelectronic modulator.
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Let us consider the use of a three-dimensional carrier in a modulator,
with a small period (T � d). In this case, the orientation of the
carrier is possible algng an axis in which are situated the channels of
Che modulator, and in the direction perpendicular to it. Practical relia-
zation of a modulator with a small period of carrier depends on the nature
of the preliminary signal proceasing and the type of modulating medium.
Let us consider optoelectronic modulators. If nonlinear processing and electron
beam recording are used in the system, the three-dimensional frequency can
~
be obtained as a result of linear change in the frequency of the reference
field. Three-dimensional modulators of this type are based on the longitu-
dinal optoelectronic effect. The electron beam governs the three-dimensional
distribution of potential on the surface of fihe optoelectronic modulator.
The passing light flux is modulated in conformity with the recorded potential
relief. The situation is much more complicated with optoelectronic modulators
operating in real time, which use linear processing of the signal and time ~
modulation. To obtain a three-dimensional carrier with sma11 period here,
it is�_necessary to greatly expand the number of, channels of the modulator
as compared to the number of array elements; this, in turn, requires the use
of dividers which can be used to distribute the signal of each array element
to several modulator channels. In the sector between tr.e divider and the
modualtor are introduced phase shifts; using them, a three-dimensional
carrier frequency is established. In this way, in optoelectronic modulators
operating in real time, the production of three-dimensional frequency runs
up against real problems.
In ultrasonic modulators, the three-dimensional carrier is realized more natu-
rally: it is a propagating ultrasonic wave. In these modulators, a very high
degree of three-dimensional filtration of light fields is achieved, and the
angle of deflection of light flux equals 6=� a ( A is the wavelength of
n
ultrasound). In most antenna problems solved using optical devices, high separa-
tion of sectors of uniqueness of depiction is necessary. Therefore, when
~ evaluating the basic indicators of optoelectronic and acoustooptical modulators,
this notion is decisive. In this comiection, it is advisable to examine
several basic properties of acoustooptical modulators.
Several Properties of Acoustooptical Modulators
Let us consider the most essential properties of ultrasonic modulators. In
optical signal processing devices of multichannel antenna systems, it is
very important to obtain a very high isolation between modulator channels
(up to 20 dB), to insure nearly complete identity of channels, processing
of broad-band signals and long signals. Let us estal~.lish a connection
between these requirements and the modulator parameters which correspond
to them.
The question connected with isolation between channels becomes especially acute
as the width of piezo transducers is reduced (and their installation spacing)
in a multichannel modulator, aince with the decrease in transverse size of
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of the piezo transducers the so-called piston zone is reduced. Let us note
that the linearity of modulation conditions, i.e., transmissions in the optical
information range about amplitude-phase distribution of the SHF field in
elements of the antenna, can be achieved while operating in the piston zone
of piezo transducers of an acoustooptical modulator. The solution of this
problem is faund by using a waveguide type ~dodulator design, i.e., by using
separate sou~dguides for each soundguide channel. To manufacture waveguide
modulators, materials are required which allow mechanical and optical treatment
nad have enhanced hardaess. Furthermore, let us note that with a width of
- piezo transduers less than one millimeter,.the manufacture of a waveguide
- type modulator is a complicated technological ~ob. In some anisotropic
crystals~ the required values of isolation between channels are achieved
by selecting completely defined directions of propagation of the acoustic
wave. Thus, in paratellurite with a direction (110) and diffraction of
light on a longitudinal ultrasonic wave, monoblock multichannel modulators
can be realized using almost any technically feasible width of piezo trans-
ducers. Crystals of lead molybd~enate can be used in the same ma.nner.
Satisfaction of the requirements of linear reproduction of amplitude and
phase relationships, retention of the dynamic range and signal-to-noise
ratio is connected with the selection of a material having high value of
the coefficient of diffraction activity M2[10]. High diffraction activity
enables us to excite ultrasonic wavea witH low values of signal input power.
Let us mention that the increased diffraction activity is promoted by the use
of diffraction conditions in the modulator, close to Bragg diffraction. It
is especially important to shift to Bragg diffraction in multichannel modulators
used to correct distortion in optical range antennas [11]. It should be
added that to retain the desired signal-to-noise ratio and dynamic range,
inherent light noises of the modulator arising from the background of the con-
stant component of light flux should be reduced to the minimum. The back-
ground can be reduced by increasing the angle between the diffracted flux and
the flux of constant component, which is achieved by increasing the ultrasonic
frequency and reducing the rate of ita propagation in the medium. Of all
currently known materials, paratellurite has the lowest rate of propagation
of ultrasound. In this c~ystal there is a direction where sound propagates
at a velocity of 0.6 x 10 meters per second. Calomel cryatals also have
parameters close to paratellurite. Furthe~more, an extremely effective method
of suppressing the constant component is the use of anisotropic diffraction
with rotation of the polarization plane in the diffracted light beam.
The requirement of processing broad-band signals is solved mainly by an ap-
propriate increase in the mean frequency of altrasound. To process signals
of great length, soundguide media should be used which have a low rate of
propagation on the one hand, and low attenuation of ultrasound on the other.
To these requirements we should add the requirements common to all kinds of
light modulators: transmittance in the proper range of light wavelengths.
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The functional possibilities of coherent optical systems for processing signals
of antenna arrays is largely determined by the information input device.
The use of ul~rasonic modui~tors enahl,es the maximum utilization of the possibility
of optical systems in tackling antenna problems and some related questione.
References
1. Lambert, Arm, Aymet. OptQelectronic processing of signals in phased
antenna arrays. ZARUBEZIiNAYA RADIOELEKTRODTIKA 1968 No 8. ,
2. Bakhrakh, L.D., Mogil'nikova, K.I., Novosartova, I.A. and Rudneva,
S.G. Some questions of focal syntheeis. VOPROSY RADIOELEKTRONIKI,
- SERIYA OT, 1970, No. 12.
3. Bakhrakh, L.D., Kremenetskiy, S.A. Some problems of focal synthesis.
RADIOTEKHNIKA I ELERTRONIKA 1972 vol. XVII No 8.
4. Levis. Optical method of signal processing for directional systems with
circular arrays. ZABRUZHNAYA RADIOELEKTRONIKA 1970 No 11.
5. Bakhrakh, L.D,, Rudneva, S.G., Shverin-Kashin, V.B,. On the possibility
_ of constructing an optical device for processing signals of circular
antenna arrays. VOPROSY RADIOELEKTRONIRI, SERIYA OT, 1979 No 3.
6. Bakhrakh, I..D., Kurochkin, A.P. On the use of ogtical systems and methods
of holography to recovery beam patterns of SHF antennas by measuring
the field in the Fresnel region. DAN SSSR 1966 vol. 171, ed. 6.
7. Cutrona, L.J., Leiht, E.N., Porsello, L.J., Vivian, W.E. On the applica-
tion of coherent optical proceeding techniques to synthetic-aperture
radar. PIEEE 1966 v. 54 No 8.
- 8. Kurochkin, A.P., Troitskiy, V.I. On the apsects of recorddng complex
distributions in a three-dimensional carrier frequency. RADIOTEKHNIKA
I ELEKTRONIKA 1969 vol. XIV No 4.
9. Kurochkin, A.P., Optical simulation of an SHF antenna. RADIOTEKHNIKA
I ELEKTRONIKA 1968 v. XIII No 7.
10. Utida, N., Niidzeki, N. Materials and methods of acoustooptical deflec-
tion. TIIER 1973 v. 8 No 8.
11. Bakhrakh, L.D., Qvezov, O.B., Rudneva, S.G. and Shverin-Kashin, V.B.
Correction of SHF antenna fields and optical antennas using ultra-
sonic modulators and holographic filters. in: Radio i akusticheskaya
Polografiya [Radio and acoustic holography], Leningrad, "Nauka" 1976.
COPYRIGHT: "Radiotekhnika", 1981
8617
CSO: 1860/339
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COMMUNICATIONS~ COI~iUNICATION EQUIPMENT, RECEIVERS
AND TRANSMITTERS, NLTWORRS, RADIO PA~SICS, DATA
TRANSMISSION AND PROCESSING, INFORMATION THEORY
UDC 621.391.82:621.396.6
DETERMINING PROBABILITY OF INTERMODULATORY INTERFERENCE IN A RECEIVER
Moscow RADIOTEKHNIKA in Russian No 2, Feb 81 (manuscript received after
completion 25 Jun 80) pp 70-73
[Article by V. I. Voloshin]
[Text] In evaluating the electromagnetic compatibility (EMS) of radio devices
(RS) of communications complexes, it is necessary to determine the probability
of intermodulatory interference in receivers (IP) which occurs when several
RC complexes are transmitting at the same time [1-3]. Because complexes
usually use RS of various ranges and IP are generated by intermodulatory
emissions (II) of various orders, in contrast to [2] we will noz impo~e
, constraints on the ranges of operating frequencies of RS and ordprs of II.
Furthermore, we will limit our examination to the frequency-energy conditions
of IP wlnerability of a receiver for complexes of closely situated narrow-band
RS, power of extraneous emissions and the sensitivity of side channels of
which are extremely attenuated as eompared to the output of basic emissions
and sensitivites throughout the primary channels. It can then be considered
that IP occur only as a result of II entering the primary reception channel,
- having been formed during interaction of primary emissions of the transmitters
in their output circuits [4]. When necessary, incidence of II can enter other
channels of receptton.
The frequencies of II ar~sing in simultaneous transmission of several (m) RS
equal
. 1 a 1k...t - ~~!a kf o"E- 1 f c ~ 1~
where fa, fb, f~ are frequencies of the ath~ bth~ ~th RS transmitting;
i= 1, 2, k, 1=� 1, � 2,
~et us designate the minimal and maximal frequencies of the range of the ith
RS accordingly of fin and fi~ and let us designate
. _ .
- _ . _ _
a~i -!t. - fte, J? - 2 Urd + ft.)~
ru1k...~'- ~fa kIe -I- IJi~ f~ ~fa k~b -I- -}-1J~, ~2~
~rR...~
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To determine the probability denaity of II frequency fu i k..,1~ let us use
relationships for the probability deneity of functione of random valuea (5] and
consider that RS frequeacies of comple.xes, when evaluating EMS, can be con-
sidered evenly distributed random independent quantities [6]. Based on (1)
and (2), we find that
_ _
~v rk...? � w�ek...t W~tk...r (-f)~ J~ 0. (3)
where for the case of simultaneous transmission of two RS (m = 2)
. f_~~
npN c~ ~ f < c~.
~�~k (I) ~ ~ ( k I lleele ~4~
max (lefa~ ~ k(~1bI �PN ~f S Iatk~
. - -
- Intk- 2~lAfa ( k I ela), � lntk- 2 1 refo- ~ k ~ DIb I� ~5)
With simultaneous tranamiesion of three RS (m ~ 3), the functions W~u i~(f)
are determined by relationships cited in the table for a series of frequently
encountered cases. One of these cases under the least common conditions is
examined in [7J. In the tabular formulas
.`I"~arat- 2 TI/~1-1,4; (6)
r11-r~4 are the set of numbers ~1--~4 arranged in decreaeing order:
E,~re~Q+lkl~Ie+lllsf~, E,-Ilefa+lklelb-IlleJ~l:
x~=IiaJa-Iklefe+l~lal~l, E.-Itela-IkiaJb-Ir~e~~l� (7)
? ~
- Relationships for W uik...1~f) are cited for f~ f uik...l~ because these
functions are symmetrical with respect to f uik...l'
At m> 4, the probability density of W~ (f) can be determined by me-
uik...l
thods presented in [8].
Frequency-enegy conditions of the presence of IP have the form:
~ f uik.,.1- .f / ~ ~ ~F~it...1 ~ t -I- ~ k ~ . � . -1- ~ l I ~ 9mar (g ~
Here f~ is the tuning frequency of the jth receiver; L1F~~ik...1 and qmaX is
the maximum detuning between II frequ~ncy and receiver tuning frequency and
the maximum order of II at which the action of IP appears (in intolerable
limits reception quality deteriorates in the given sense). Since output
circuits of transmitters are generally rather wide-banded and the levels
of attenuation of II become normal only for a specific relationships of fre-
quencies of transmitters fa, fb, ...f~ [9, ~.0], the relationship of DF~ik...l
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a ~
~ ~ .
a , ~
n ~ t
v ' ~ I ~
a y ~ '
_ � ~ _ a ~ ~ � ^ �
~ ~ -
r ~ ~ F
: ~ r . I a
Q ~ Iw~
~ r ~
\ I , I~ Q
t . ~ ~a
u ~
~ - y
w ~
~
O ~ ~ ~v
~ ~ ' .
y ~ .
y II ti ' ~cr
~ ~ . a ~ ~
a n .
_ ~
- o ~ � .
~ ~ �
. a
a
O y
i'~ ~ _ �
r ~ O
_ ~ a . 4 a � .
_ � ,'1 _ � a ~
a a y~oc c Q o I u
V a ~ ~ ~ - ' ~ ^a ~
^ - - ^-1 ' ~ a " o
Q cV r ~ '1 ~
a � V ~ Q ~ C , I I G
e-~ ~ o a ~ p
\'~i ~ ~ r .i ~
w' oe K a v a � 4.
W q I ~
A Q E ~ I,y ~ �rp~ a ~ ~ ,
~ V v ~ ' r
H o ~ ~ d
c ~ p ~ y
E a a u eKp IN v . �
_ _ � E ~
v ~
,
a ~
O -
d d a ' r1 , ~ Q .
- -0c - a ~ p `r
~ h ti ~ ~ ' .
~
v ~ i . ~ r Q . O '
b . O O ti1
\ S v O , I Q . d '
d t C ~ ~ d ~ ~ ~ �
s ` � ~
a E - � � .
+ - . . tl �
V V
~ ~ ~ b � a .
` d C . . a�~ I~ ' v `
~
K
- K ~ .
_ ~o C
C
1 S Q
= 5, S ~ � w r ~ '