CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
FREQUENCY-CODED RADAR CLEAR FREQUENCY SELECTOR
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A graduate ~ork project submitted in partial .sat~
isfaction of the requirements for the degree of
Master of Science in
Engineering
by
Charles Matthew Holmes, Jr.
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'The graduate work project of Charles Matthew Holmes, Jr.
is approved:
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C.l\.LIFORNIA S'I'.A'I'E UNIVERSITY, NORTHRIDGE
Nay, 1975
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'l'A,BLE OF CONTEN'l'S
LIST OF' SYMBOLS •.•
ABSTRACT . ... " .
.I!\fTRODlJC'I.'ION.
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PRINCIPLE OF OPERl\.TION •••••••••••••••••••••••••• 3
EQUIPMENT EMPLOYED IN TESTING .•..••••••••••••••• 8
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. TESTING PROCEDURES ••••••••••••••••
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DISCUSSION ...••.•••..••••
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BIBLIOGR...T'iPHY.
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APl'ENDIX ......... . . . . . . . . . . • ~ . . . . . . . ~. ~ . . . . . . . . . . . . 24
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LIST OF SYMBOLS
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Hz
Hertz
kHz
Kilohertz
MHZ
Megahertz
PRR
Pulse repetition, rate
dB
Decibel
DINA
Direct noise amplif.ication
CFSC
Clear frequency
select circuit
TW'r
'!'raveling wave tube
RF
Radio frequency
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ABSTRACT
FREQUENCY-CODED RADAR CLEAR FREQUENCY SELECTOR
by
Charles Matthew Holmes, Jr.
Master of Science in Engineering
May, 1975
1'1
This graduate work project report deals with the test
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evaluation of the clear . frequency selec·t portion of
the frequency-coded radar simulator in an environment of
noise j annning.
During the project, tests were conducted on the
circuitry to determine its capability of selecting the
clearer frequency band of a two band radar simulator when
noise jammiri.g Kas present.
The clear frequency selector
was evaluated in an environment of direct noise amplification (uiNA)
jamming and swept noise jamming.
The objective \vas to det.ermine hmv ·t:q.is circuit will
respond to both constant noise and sweeping, intermittent
noise.
The alternate objective was to determine how much
noise power is needed on one frequency band to initiate
the selector into switching to the alternate band.
The background information as to how this clear
. frequency selector originated and its principle of
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operation are presented in this report.
The testing pro-
cedures and the test equipment used are thoroughly described.
The results obtained from the tests and the con-
clusions drawn are described in detail.
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INTRODUCTION
There is a need for defense purposes to avoid certain
types of noise· j arnming in the usage of radar.
If a
• radar can be designed to operate on two or more frequency
ba.nds, the bands that experience little or no jam>Tting can
be used for operation in lieu of the heavily
ja~ned
bands.
To do this, a circuit will be needed that is capable of
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determining the extent of the jamming on each band and
automatically switching to the "clearer" bands.
A circuit designed for these purposes, called a clear
! frequency
selector, was proposed several years ago by
l_engineers concerned with electronic warfare.
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A crudely
designed prototype was assembled, tested, and improved.
~As
additional testing progressed, more improvements in
design were made until the completed circuit, as it now
exists, was eventually achieved.
To test this circuit,
a frequency-coded radar simulator was assembled by interfacing various pieces of test equipment.
This radar
sdmulator is capabl~ of operating on two frequency bands
and, with use in conjunction with the clear frequency
selector, is capable of S'f.vitching to the nonjammed
frequency band whenever noise jamming is present.
Since no additional testing had been conducted on the
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clear frequency selector after the last design improvement,
evaluat~on
was now needed on this latest prototype
in an environment of several types of noise jamming.
Therefore, this paper will describe the tests made on
this particular circuit, the techniques involved, the
results 1 and conclusions.
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PRINCIPLE OF OPERATION
The
fr~quency-coded
radar simulator
operate~
on two
frequ"ency bands designated band A and band B; each band
is 200 MHz wide.
were
cho~en
The center
frequ~ncies
of each band
so that available test equipment could be
used to construct the radar simulator.
The 200 MHz
spectrum was chosen because a wide bandwidth such as
·this would be more difficult to jam with noise ·than a
narrower one.
The principle of operation of the radar simulator
is to passively "listen" to the environment on band A
for 256 microseconds, sample and store this information.
It then repeats this process for band B.
The d'ata from band A and band B are compared and
the circuitry within the radar simulator makes a decision
as to which band experiences the lesser noise jamming.
The clearer band is then selected for transmission the
next time the transmitter simulator is gat.ed on.
After
each pulse is "transmitted," the radar receiver "listens"
for a duration of time for the pulse to be reflected from
a target.
After this duration of time, the receiver will
once again sample the environment on band A and band B
.
---b~e-f_o_,_·e~he
transmitter transmits
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decision is made as to which band will be used each time
the transmitter is on.
The timing sequence of the fre-
quency-coded radar, its transmitter, and its receiver are
seen in Appendix A, B, and C, respectively.
This operation is accomplished by the clear· frequency
select circuit shown in Figure 1.
The 200 MHz spectrum
of the radar simulator is divided up into 15 channels,
with each channel 13.33 MHz
wide~
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During each pre.look:,
the circuitry of Figure 1 is reset and the output of the
band A receiver is fed to a read-only memory {ROM) circuit which indicates, by producing a four-bit binary word,
how many of the 15 channels experience noise jamming.
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- high output corresponds- to- channel detection..
A
This fou:c-
bit word is fed to a full adder which adds each count to
·the previous count each time a clock pulse is received.
Thus, a total count of how many channels experience jamming during the specified 256 microseconds is obtained.
The total capacity of data is 3840 bits (256 x 15).
The
output of the full adder is then entered into the store
band A register, the adder is reset, and the process is
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repeated for band B.
The magnitude of each storage is
compared and three outputs are obtained:
B, A less than B, and A equals B.
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greater than
If A is greater than
B, transmit band B will become high.
B, transmit band
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will become high.
If A is less than
If A equals B,
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STROBE
MAGNITUDE
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FIGURE. 1 '
CLEAR FREQUENCY SELECT CIRCUIT
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the output of the band select circuit will stay high on
whichever band was last high.
~he
timing sequence for
this clear £requency select circuit is shown in Figure 2.
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A
STAOOE COMPARATOR
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TIMING
SEQUE~CE
FIGURE 2
FOR CLEAR FREQUENCY SELECT CIRCUIT
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EQUIPMENT EMPLOYED IN 'fESTING
The objective of the tests was to evaluate the performance of the clear frequency select portion of the
frequency-coded radar simulator.
Therefore, it was nee-
essary to measure the band selectivity of the clear
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frequency selector as the power of noise jammers operatinsr\
on the two frequency bands was varied.
Since it was necessary to evaluate the radar simula-
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tor in an environment of constant noise and swept noise,
two laboratory-built jammers were used.
One of
~.:he
jam- .
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rners was a Direct Noise f.._mplification {DINA} jammer,
which!!
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·vms designed to operate on band B of the radar simulator.
'This j
amm~r
was constructed by cascading an li.LFRED Model
503 travelling wave tube an!plifier with a Watkins Johnson
'rype HJ-286 low noise amplifier and using the resultant
noise output.
The output of t.his jammer operated into a
400 MHz wide band pass filter with its center frequency
that of the center frequency of band B.· 'I'he band pass
filter· was used merely to concentrate the noise spec·trum
about band B instead of having an infinitely broad spec·trum of noise.
The other jammer used was a Swept Noise
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325A sawtooth generator that has a sweep rate from 100 Hz
to 500 kHz, an ALFRED Model· 265 regulated pmver supply,
and a laboratory built: backward wave oscillator assembly.
This jammer was programmed to sw·eep a 10 MHz noise spectrum a total bandwidth- of 200 HHz using a sawt.aoth modu...;..
lation.
'l'hese jammers 1 connected in series with two HewlettP~ckard
J732A variable attenuators,are shown in Figure 3
along with the CMC Model 901 counter-timer as they were
connected for testing purposes.
The procedures involved
will be described in the section titled "Testing Procedures~"
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FIGURE 3
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ASSEMBLY
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TESTING PROCEDURES
To measure band selectivity of the system, it. was
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essary to determine the percentage of time t.he frequencycoded radar simulator would operate on one band if the
opposite band received noise jamming.
It was also nee-
essary to determine the amount of time the radar simulator
vmuld spend opera·ting C?n ba:nd A and B if both bands rec-
ei ved unequaJ.--jammi:ng.
Lastly r it I.1ra,s necessary to deter-
mine how the selectivit:y of the
sysb:~m .\<.Tas
affected as the
sweep frequency of the swept j arrrrner was varied.
In the clear frequency select circuit (Figure 1) , the
"transmit band A" and "transmit band B" outputs would be·come· high when the radar. simulat:or was both transmitting·
and
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listening" on band A .• and transmitting and "listening"
.bn band B,
resp~ctively.
Therefore, it was necessary to
construct the circuit shown in Figure 3 for testing the
In this circuit, "XMIT
frequency-coded radar simulator.
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A/B" would become higl1 whenever the radar simulator was
bot.h transmitting and "listening.
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But t.he PRR would be-
come high only when the radar !';j.mulat.or was transmitting.
As a. result, the output of the AND gate \'JOuld become high
only wheri the radar simulator was transmitting on band A
or band B.
Therefore, the counter-timer would count the
number of transmits on ba11d A or B for a specified period
of t.ime.
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To determine the probability of operating. in a
certain band if the radar simulator recei-...red jamming,
a series of 30 second tests was conducted. 1
The pulse
repetition rate was multiplied by 30 to obtain the max~
imum number of pulses the
rad~r
transmitting in 30 seconds.
simulator is capable of
The counter-timer was then
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placed at the output of the radar transmitter toobtain
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the actual· number of pulses the radar Simulator transmits
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in 30 seconds.
This count was repeated 15 times to obtainll
a reasonable average.
This average was then considered
to be the maximum number of pulses the radar simulator is
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capable of transmitting on either band in a petiod of 30
seconds.
If, for any reason, a smaller number of pulse
counts is made on either band in a 30 second P Prl·
_ od, t.he
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probability of transmitting on that band can be calculated!
by dividing this count by the average obtained above.
put of the AND gate to obtain the number of times the
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The length of time of the tests was arbitrarily
chosen.
Longer tests would have resulted in more
accurate data.
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radar simulator would t.ransmit in band 1'-.. for a 30 second
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period if band B received greater noise jamming- than band
A.
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In order to do this 1 band 1>. was initially jammed
(Band B was now automatically selected for transmission
100 percent of the time) •
The jammer in band B was then
turned on and the jamming power was increased until the
counter indicated band A was clearer about 3 percent of
the time.
_This jamming power in band B was recorded and
the number of transmit counts obtained·in.a 30 second
interval in band A was also recorded.
The power in b-and
B was then increased in certain increments and rec6rded
while the counts in band A were also recorded.
these counts was divided by the
average
Each of
'maXirtmm number
of-~
pulses ca.lculated above to obtain a probability of transmi tting in band A if
certain level.
thE~
jamming power in band B was at a
'£his j anuning pov1er in band B was then in-
creased until band
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cent of the time.
'l'hese tests were conducted using swept_
\.Yas chosen for tra:nsmissi(;n 100 per:-
jammer sweep rates of 500 kHze 100 kHz 1 and 10 kHz.
A·
graph was then constructed using this information with
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jarruner power increase on the ordinate and probability on
the abscissa.
swept jammer
kHz.
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Three plots
swe(~p
we~e
made on this graph for
frequencies 500 kHz, 100 kHz 1 and 10
The above was then repeated for a probability of
on band A.
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The above tests for probability of transmitting on
band B with increased jamming on band A were then repea·ted for assorted swept jammer sweep frequencies
ranging from 100 Hz to 500 kHz.
The objective was to
make a plot on 4-cycle semi-log paper of the change in
60 percent, 70 percent, 80 percent, and 90 percent.
Although these plots were not linear, interpolation was
used ·to calculate the jammer power change for these
probabilities.
It is estimated that the error intro-
duced by using interpolation is very slight.
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RESULTS & DISCUSSION
The graph showing how the probability of. transmitting
on a certain band varies as DINA jamming on the opposite
band varies is shown· in Figure 4.
this graph is shown in Figure 5.
The expand(':!d view of
1·he graph showing how
the probability of transmitting on a certain band varies
as· swept jamming on the opposite band varies is shown in
Figure 6.
Figures 4 through 6 show how the probabilities
vary as the sweep frequency of the swept jammer varies.
Although the DINA jammer power is dominant in Figu-res 4
·and 5, swept power is still present on the opposite band
so that a det:e:r:mination of how the radar simulator reacts
to both types of jamming can be obtained.
Likewise, in
Figure 6, DINZ.i jamming is also present on the opposite
band.
Figures 4 through 6 show that a swept jammer requires
a greater increase of power than does .::; DINA jammer to
cause the
frequency~coded
radar to transmit on the oppos-
ite band 100 percent.of the time.
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ja~~er,
This is because, with a DINA
ously present.
noise is continu-
However, since the receiver bandwidth
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is 200 MHz and the noise bandwidth of the swept jammer is
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only 10 MHz, only part of the spectrum of the radar simulator redeives noise
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any one time.
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This is further
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-Bubstantiated in Figure 6.
In thj s gra.ph, a great.er
increase of januner power is required to achieve 100
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percent probability v.'hen the swep·t jammer is sweeping at
a rate of 10 kHz than when it is sweeping at a rate of
500 kHz.
Although the noise spectrum is only 10 MHz wide,!
·the radar simulator receives noise ]J1ore often at a 500
kHz rate than at a 10 kHz rate.
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Therefore, from Figures
4 through 6, it is concluded t.hat the DINA jammer has a
greater ipfluence on the frequency-coded radar
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than does the swept jarM1er when the latter is sweeping
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at a rate of 500 kHz or less.
The gra.ph of change in swept j arnmer power versus swept.
jammer sweep frequencies is shown in Figure 7.
This graph
shows a sharply decreasing slope from 20Q Hz to about
2 kHz for all probability levels.
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Figure 7
Plat of Cha.nge in Jammer Po~t1er vs. Jammer Sweep Frequency on Band A for
50%) 60%, 70%, 80% & 90% Probabilities of Transmitting on Band B
L._ _ _ _,
·-----'--------------·--·----------------.
r
!-->
0
21
Above this latter sweep frequency, the slope begins to
decrease,so·that the increase of jammer power required
II
to maintain a certain probability level gets increasingly smaller as the jammer sweep frequency increases.
Above 2 kHz, almost all probability levels coincide:
indicating that a very small increase of. jammer power
will cause the frequency-coded radar to tra.nsmit more
often in the frequency band t.hat is not being jammed or
has the lesser jamming.
At a jammer sweep frequency of
about 100kHz andabove, all probability levels almost
overlap,indicating that a power increase of less than
ldB will cause the radar simulator to transmit in the
.clearer band up to 100 percent of the time.
Therefore,
from Figure ?,it is concluded that the increase of
swept jammer power required to cause the frequency-coded
radar to transmit in the clearer band decreases as the
sweep frequency increases.
L_
_______________I
\
r-----CONCLUSIONS
In an environment in which constant noise (DINA)
j
ammi~1g
is present, the clear frequency select portion
of the frequency-coded radar simulator has the ability
to switch to the clearer band very quickly.
In tests
-conducted, the probability of transmittin<J on the
clearer band rose from zero percent to·lOO percent with
a ldB increase of jamming power.
a power increase of 1. 26 times.
under
actua~
This is equivalent to
Since noise januners used
conditions transmit power in the hundreds
of \vatt.s,. the clear frequency selector would switch tothe clearer band instantaneously.
Hov1ever, in an environment of swept noise jamming,
the speed.with which the clear frequency selector switches
to the clearer band is dependent upon the sweep speed of
i:he jamr.1er.
Faster sweep rates 1 \vhich are required for
more effec·ti ve jamming, will cause faster svli tching to
the clearer band.
I___________________ _
I
(
22
...--------------------------·--------
l
BIBLIOGRAPHY
Skolnik, Merrill I.
Introduc~ion to Radar Systems.
New York: McGraw-Hill Book Co., Inc., 1962
TP~73-54 Countermeasures Progress Report CounterCountermeasures 'I'echnology. February-Apri.l--197 3-
TP-74-33 Countermeasures Progress Report CounterCo~nt~rmeasures Technology.
November 1973:=;January 1974.
SMS-TG-670-01 Introduction to CCM Operational Techniaues.
September 19 6 7 -.-.--------·----···--------··"--.-·-----·------------~----
23
j
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APPENDIX
II .
I
24
-·
Ir - - - - · - --
1
I
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II·
·------------~------------
Transmitter and Receiver operate on t\·:c bands (A&B)
each band 200 MHz wide. Which band receives less
jamming is the band the Transmitter &Receiver
next.operate.
.AI
Transmitter
r~r L _____
Ii
l
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!
Period
+--.
Receiver
.
Loca1 Oscillator
__,,
·----------------------~~
__
~ AOr B
I
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' r2_5_6' mj
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1
local Oscillator
Listen A
·
1 ·..
-----1,
cro$.e.c.ol'
A
.....___ _ _ __
I
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Local Oscillator
Listen B
If A is less than B Next
listen B; decide.
puls~
transmit A; receiver local.ostillator on A; listen A;
If A is greater than B Next pulse transmit 8; receiver 1oca1 oscillator on B; listen
A; listen B; decide. APPENDIX A-Timing Sequence F' ..requency Coded Radar
L--------·--
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