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ECCM IN RADARS

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1/119 ELECTRONIC PROTECTION
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ELECTRONIC PROTECTION

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• DEFINITION : ECCM IS THE ACTION TAKEN TO

ENSURE FRIENDLY EFFECTIVE USE OF THE EM

SPECTRUM DESPITE THE ENEMY’S USE OF ECM OR ESM.

• IT IS DEFENSIVE ARM OF EW

• ECM AND ECCM DEVELOPMENTS ALWAYS FOLLOW

EACH OTHER.

• ECCM : MOSTLY CONCERNED WITH TECHNIQUES

WHICH ARE BUILT IN DURING THE DESIGN OF

ELECTRONIC EQUIPMENT

• ECM : WHEREAS, ECM USUALLY REQUIRES

SEPARATE EQUIPMENT WHICH IS DEVELOPED ON THE

ESM DATA COLLECTED ON THE ENEMY EQUIPMENT.

ECCM

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• ECM AND ECCM DEVELOPMENTS ALWAYS

FOLLOW EACH OTHER

• THE ABILITY OF A RADAR OPERATOR

IMPORTANT TO

• TO RECOGNISE AN ECM BEING USED BY

THE ENEMY WITHOUT LOSS OF TIME

• USE THE BEST SUITED ECCM AVAILABLE

TO HIM WHICH WILL PROVE TO BE THE

DECIDING FACTOR

ECCM

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•PREVENTION OF RADAR SATURATION

•ENHANCEMENT OF SIGNAL TO JAMMING RATIO

•DISCRIMINATION OF DIRECTIONAL INTERFERENCE

•REJECTION OF FALSE TARGETS

•MAINTENANCE OF TARGET TRACKS

•COUNTERACTION OF ESM

•RADAR SYSTEM SURVIVABILITY

OBJECTIVES 0F ECCM

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ECCM TREE

Antenna Related ECCMs

ECCM

ANTI ESM ANTI ECM

EEP EESOperational Measures

Training

MeasuresTechnical Measures

Receiver Related ECCMs

Transmitter Related ECCMs

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ANTI-ELECTRONICS

SUPPORT MEASURES

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ECCM IS TO COUNTER AND DETECT THE ENEMY

ESM ACTIVITY BY

• JUDICIAL IMPOSITION OF

ELECTRONIC EMISSION POLICY (EEP)

• AND MEASURES INVOLVING ELECTRONIC

EMISSION SECURITY (EES)

AIM OF ANTI-ESM

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ELECTRONIC EMISSION POLICY

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•ELECTRONIC EMISSION POLICY (EEP) IS A COMMAND FUNCTION.

•IT LAYS DOWN RESTRICTIONS ON THE USE OF ELECTRONIC SYSTEMS OF OPERATIONS.

•IT IS EVOLVED AT THE FIELD FORCE LEVEL AND IS CONVEYED TO THE LOWER FORMATIONS THROUGH OPERATIONAL ORDERS AND INSTRUCTIONS

•EEP IS THE POLICY WHICH LAYS DOWN

• DEGREE OF FREEDOM ALLOWED IN THE USE OF ELECTRONIC SYSTEMS TO COUNTER ENEMY’S CAPABILITY TO DETECT, IDENTIFY AND LOCATE OWN EMITTERS FOR EXPLOITATION BY HOSTILE ACTION AND EXERCISE CONTROL OVER OWN EMISSIONS TO MINIMIZE ELECTROMAGNETIC INTERFERENCE

EEP

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•IT REDUCES THE REACTION TIME AVAILABLE TO THE ENEMY

ESM ORGANIZATION

• TO ACQUIRE INTELLIGENCE

• STUDY THE TECHNICAL PARAMETERS OF OUR

ELECTRONIC SYSTEMS. 

•IT DENIES INTELLIGENCE THAT MAY BE GAINED BY THE

ENEMY THROUGH INTERCEPTION. 

•IT ENABLES A BETTER CONTROL ON ALL EMISSIONS AND

THERE BY HELPS TO REDUCE THE PROBLEMS OF EMI

PURPOSE OF EEP

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BASIC CONSIDERATIONS FOR EEP

•THE OPERATIONAL NECESSITY TO OPERATE AN ELECTRONIC EQUIPMENT

•THE RISK OF INTERCEPTION OF FRIENDLY EMISSIONS BY ENEMY’S ESM RECEIVERS

•THE VALUE OF SUCH INTERCEPTIONS TO THE ENEMY COULD BE A DECIDING FACTOR IN THE JUDICIOUS USE OF FRIENDLY ELECTRONIC EMITTERS.

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•THERE SHOULD BE SEPARATE PEACE TIME AND WARTIME POLICY.

•THIS POLICY SHOULD BE CONSTANTLY UNDER REVIEW AND LINKED UP WITH THE CHANGES IN THE ENEMY CAPABILITIES AND NEW TECHNICAL DEVELOPMENTS.

•EEP IS NOT STATIC POLICY.

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ELECTRONIC EMISSION SECURITY

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ELECTRONIC EMISSION SECURITY (EES)

ONCE THE EMISSION POLICY HAS BEEN DECIDED MEASURES

ARE TAKEN TO ENSURE THAT THE ENEMY’S ESM

ORGANIZATION GETS THE LEAST POSSIBLE INFORMATION

FROM OWN ELECTROMAGNETIC TRANSMISSIONS. THIS IS

KNOWN AS EES. THE BASIC CONSIDERATIONS FOR EES ARE :-

(A) THE DIRECTION OF TRANSMISSION.

(B) THE FREQUENCIES OF TRANSMISSION.

(C) SECURITY OF TYPES OF EMITTERS AND

CHARACTERISTICS OF ELECTRONIC SYSTEMS.

(D) OBSERVANCE OF SECURITY RULES AND SAFETY

MEASURES.

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ANTI-ELECTRONIC COUNTER MEASURES

AIM OF ANTI ELECTRONIC COUNTER MEASURES IS TO REMOVE OR REDUCE THE EFFECTIVENESS OF THE ENEMY’S ECM. THESE COUNTER COUNTER MEASURES HAVE FOLLOWING THREE ASPECTS:-

•ORGANIZATIONAL.

•TRAINING.

•TECHNICAL.

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ANTI-ELECTRONIC COUNTER MEASURES

ORGANIZATIONAL ASPECTS

•FREQUENCY DIVERSITY AND PROCEDURE FOR CHANGING OVER TO ALTERNATIVE FREQUENCIES WITHOUT CAUSING CONFUSION.

• PROCEDURE FOR IMPOSITION OF RADIO SILENCE.

• PROCEDURE AND ORGANIZATION OF GETTING D/F CUTS IN CASE OF JAMMING BY MORE THAN ONE RADAR IS EXPERIENCED. 

• DESTRUCTION OF JAMMER ON PRIORITY. 

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ANTI-ELECTRONIC COUNTER MEASURES

ORGANIZATIONAL ASPECTS

• LOCATION OF RADARS TO PROVIDE BACK UP TO EACH OTHER.

• PROVISION OF ALTERNATIVE COMMUNICATION CHANNELS. 

• USE OF HIGHLY MOBILE EQUIPMENT WITH PRE-SELECTED ALTERNATE SITES.

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ANTI-ELECTRONIC COUNTER MEASURES

TRAINING ASPECTS

• TRAINING OF OPERATOR IN REALISTIC ECM ENVIRONMENT.  

•TRAINING CO-ORDINATION OF ECCM EFFORTS.

•TRAINING IN SECURITY ASPECTS. 

•THE OPERATOR SHOULD BE ABLE TO RECOGNIZE AND REPORT JAMMING. 

•ABILITY TO WORK WITH MINIMUM POWER TO AVOID DETECTION. 

•ABILITY TO RECOGNIZE OWN RADAR AND COMMUNICATION SIGNATURES. 

•HIGH MOTIVATION.

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ANTI-ELECTRONIC COUNTER MEASURES

TECHNICAL ASPECTS 

THE MOST EFFECTIVE MEASURES TO COMBAT ECM IS AN

UP-TO-DATE PIECE OF EQUIPMENT OPERATED BY A WELL

TRAINED OPERATOR. FEW OF THE IMPORTANT TECHNICAL

ASPECTS COMMON TO BOTH RADAR AND

COMMUNICATION ARE:-

• CODING OF TRANSMISSION. 

• USE OF DIFFERENT MODULATIONS. 

• QUICK CHANGE OVER OF FREQUENCY AND MULTI-

CHANNEL TRANSMISSION. 

• HIGHLY DIRECTIVE ANTENNA WITH SIDE LOBES AS LOW

AS POSSIBLE. 

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ANTI-ELECTRONIC COUNTER MEASURES

TECHNICAL ASPECTS 

• HIGH POWER OUTPUT WITH SELECTIONS AVAILABLE TO OPERATE AT LOW POWER (1/4, 1/2 OR FULL POWER). 

• SELECTION OF SITE TO IMPOSE NATURAL BARRIERS TO THE ENEMY ESM ORGANIZATION. 

• MOBILITY OF THE EQUIPMENT.

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ANTI ECM MEASURES

THE MAJOR ECM THREATS TO A SURVEILLANCE RADAR INVOLVE :

(A) NOISE JAMMING

(B) DECEPTION JAMMING

(C) CHAFF

(D) DECOYS AND EXPENDABLES

(E) ANTI RADIATION MISSILES

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TRANSMITTER RELATED ECCM

•HIGH POWER OUTPUT

•FREQUENCY AGILITY

•FREQUENCY DIVERSITY

•PRF STAGGERING

•PRF JITTER

•PULSE COMPRESSION

•INCREASING TRANSMITTER FREQUENCY

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TRANSMITTER RELATED ECCM

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POWER

•INCREASING THE RADAR TRANSMITTED POWER INCREASES THE EFFECTIVE RADIATED POWER (ERP) WHICH IN TURN INCREASES THE RADAR RANGE AND THE BURN THROUGH RANGES (BTR).

•THE OPTIONS OF OPERATING THE RADAR AT 25 %, 50% AND 100% ( 1/4,1/2 AND FULL POWER ) POWER SHOULD BE AVAILABLE TO THE OPERATOR WHICH WILL GIVE THE OPERATOR THE FLEXIBILITY TO OPERATE THE RADAR AT LOW POWER TO AVOID DETECTION BY ENEMY ESM RECEIVER AND ALSO INCREASE THE POWER IN CASE OF JAMMING EXPERIENCED.

TRANSMITTER RELATED ECCM

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FREQUENCY

•TRAINING AND OPS FREQUENCIES SHOULD BE DIFFERENT.

•THE WAR FREQUENCIES COULD BE KEPT A SECRET.

•THE TWO FREQUENCIES CAN NOT BE VERY FAR APART

MAINLY DUE TO THE LIMITATIONS OF THE MICROWAVE

COMPONENTS WHICH PERMIT ONLY + 10 % VARIATION FROM THE

CENTRAL FREQUENCY, BEYOND WHICH THE COMPONENTS LIKE

WAVE GUIDE AND ANTENNA BECOMES UNMATCHED AND CAUSE

CONSIDERABLE ATTENUATION.

•THE TWO WIDELY USED TECHNIQUES AS ANTI ECM

MEASURES ARE :

• FREQUENCY AGILITY

• FREQUENCY DIVERSITY

TRANSMITTER RELATED ECCM

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FREQUENCY AGILITY

• THE ECCM TECHNIQUE WHERE THE FREQUENCY OF A RADAR IS

CHANGED IN ORDER TO FORCE THE ENEMY JAMMER TO SPREAD

HIS AVAILABLE POWER OVER A SIGNIFICANTLY INCREASED RF

BANDWIDTH.

• THE INTENDED EFFECT IS TO REDUCE THE JAMMING DENSITY.

• THIS IS ALSO CALLED FREQUENCY JUMPING, HOPPING

• THE NUMBER OF INDIVIDUAL SPOT FREQUENCIES AVAILABLE ARE

A FUNCTION OF COST.

• THE FREQUENCY AGILITY MODE MAY BE ON A BURST-TO-BURST

OR PULSE-TO-PULSE BASIS

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FREQUENCY DIVERSITY

• AN ECCM TECHNIQUE IN WHICH THERE IS A SIMULTANEOUS

OR NEARLY SIMULTANEOUS OPERATION OF ELECTRONIC

SYSTEMS PERFORMING SIMILAR FUNCTIONS AND WHERE THE

SYSTEMS NORMALLY USE WIDELY SEPARATED

FREQUENCIES. THIS MAY TAKE THE FORM OF A NUMBER OF

SEARCH RADARS OF A DEFENCE COMPLEX OPERATING AT

DIFFERENT FREQUENCIES. IT RESULTS IN SPREADING THE

AVAILABLE JAMMER POWER. IT IS ALSO KNOWS AS BAND

DIVERSITY, MULTIPLE RADAR, DUAL RADAR AND RF

DIVERSITY.

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PRF AGILITY

• IT HELPS THE RADAR TO INCREASE ITS CAPABILITIES IN A MULTI

ELECTRONIC ENVIRONMENT

• IN THIS CASE THE RADAR PRF IS CHANGED

– MANUALLY BETWEEN TWO OR MORE FREQUENCIES

– RAPIDLY VARIED AT A RANDOM RATE SO THAT FALSE TARGETS

APPEAR TO JITTER OR BECOME FUZZY ON THE SCOPE (PRF JITTER)

– SWITCHING PRF TO DIFFERENT VALUES ON A PULSE TO PULSE

BASIS SUCH THAT THE VARIOUS INTERVALS FOLLOW A REGULAR

PATTERN (PRF STAGGER). OTHER NAMES OF THIS TECHNIQUE ARE

PRF SHIFTING , PRF SLIDING AND VARIABLE PRF.

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STAGGERED PRF

• HIGH PRF RADARS ARE SHORT-RANGE TRACKING RADAR. 

• SHORT RANGE WEAPONS HAVE HIGH PRF RADARS.

• A STAGGERED PULSE TRAIN IS FUNDAMENTALLY A BASIC PRF

WITH THIS SAME PRF IMPRESSED UPON ITSELF ONE OR MORE

TIMES.

• THE NUMBER OF LEVELS (OR POSITIONS) IS THE NUMBER OF TIMES

THE BASIC PRF IS INTEGRATED IN THE PULSE TRAIN.

• EACH LEVEL HAS THE SAME CHARACTERISTIC PRF AND PW, BUT

THE TIME TO FIRST EVENT FOR EACH LEVEL IS DIFFERENT.

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STAGGERED PRF AS EP TECHNIQUE

P

false targetsPRI

variation

Scope staggered PRF

time / range

true target

false targets

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JITTER PRF

• IN JITTER MODE, THE TIME BETWEEN SUCCESSIVE PULSES, IS

ALLOWED TO VARY IN A TOTALLY RANDOM MANNER OVER A

SERIES OF SET INTERVALS AS LONG AS THE MAXIMUM RANGE

CONDITION IS MET.

• THE PRI CAN BE MODULATED BY A WELL-DEFINED FUNCTION:

– A SLIDING PRI VERY SLOWLY INCREASES/DECREASES THE PRF.

– A RAMP PRI DECREASES THE INTERVAL WITH A CYCLIC RAMP

FUNCTION.

– A MODULATED PRI VARIES THE INTERVALS IN A SINUSOIDAL OR

TRIANGULAR MANNER.

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PULSE COMPRESSION

• TO TRANSMIT MORE POWER, ( FOR LONGER DETECTION RANGE

AND GREATER BTR) PULSE WIDTH ,(PW) SHOULD BE MORE.

• HOWEVER , WIDENING THE PW HAS THE UNDESIRABLE EFFECT OF

REDUCING THE RADAR RANGE RESOLUTION.

• PULSE COMPRESSION ACHIEVES THE ADVANTAGE OF SHORT

PULSE AND LARGE RADIATED ENERGY.

• PULSE COMPRESSION IS ACHIEVED BY TRANSMITTING A LONG

PULSE CONTAINING EITHER PHASE OR FREQUENCY MODULATION

IN ORDER TO INCREASE THE SIGNAL BAND WIDTH (B) AND ON

RECEPTION THE LONG PULSE IS COMPRESSED BY A MATCHED

FILTER IN ORDER TO GET A SHORT PULSE.

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PULSE COMPRESSION

• NEXT FIG SHOWS TWO RECEIVED LONG PULSES FROM TWO CLOSE TARGETS AS THE ECHOES OVERLAP THUS CAN NOT BE SEPARATED IN RANGE AND WILL BE PRESENTED AS A SINGLE TARGET. AFTER COMPRESSION THE ECHOES ARE TIME SEPARATED AND CAN BE RESOLVED IN RANGE.

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Time/Range

Amplitude

Fig.2(b) Compressed pulse from adjacent ranges

Time/Range

Amplitude

Fig. 2(a). Received pulse from adjacent ranges

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RECEIVER RELATED ECCM

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RECEIVER RELATED ECCM

• CFAR (CONSTANT FALSE ALARM RATE)

• MOVING TARGET INDICATOR

• STC (SENSITIVITY TIME CONTROL)

• IAGC ( INSTANTANEOUS AGC)

• LEADING EDGE TRACKING

• LOGARITHMIC AMPLIFIER

• PULSE LENGTH DISCRIMINATOR (PLD)

• DICKIE FIX

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CONSTANT FALSE ALARM RATE (CFAR)

• AN OPERATOR TRACKS THE TARGET ON THE SCOPE MOST EFFICIENTLY

WHEN THE NOISE PRESENT ON THE SCOPE REMAINS CONSTANT

IRRESPECTIVE OF THE SIGNAL CONDITIONS.

• IN THIS TECHNIQUE THE RECEIVER SENSITIVITY AUTOMATICALLY GETS

ADJUSTED DEPENDING UPON THE VARIATIONS IN NOISE LEVEL. IN THE

PRESENCE OF NOISE JAMMING THIS TECHNIQUE DECREASES THE EFFECT

OF RADAR RECEIVER SATURATION AND MAINTAINS CONSTANT NOISE

LEVEL AND MINIMISES THE FALSE ALARMS.

• THIS TECHNIQUE HAS BEEN DEVELOPED TO PREVENT OVER LOADING OR

SATURATION OF RECEIVER CAUSED BY A STRONG NOISE JAMMER.

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CONSTANT FALSE ALARM RATE (CFAR)

• THE CFAR CAPABILITY IS ACHIEVED BY CONTINUOUSLY

MONITORING THE NOISE LEVEL, FINDING ITS AVERAGE

VALUE, AND INCREASING OR DECREASING THE

THRESHOLD LEVEL ACCORDING TO THE VALUE.

• CFAR HAS THE FOLLOWING ADVERSE AFFECTS:-

– AS THE PICTURE ON THE SCOPE REMAINS CONSTANT,

THE OPERATOR DOES NOT EVEN NOTICE THAT THE

RADAR HAS BEEN JAMMED. 

– NO TARGET IS PICKED UP UNLESS IT IS VERY STRONG.

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RAW VIDEO MONITORING

• CFAR RECEIVERS, THEREFORE DO NOT HAVE GOOD

ECCM CAPABILITIES.

• IN MOST OF THE AUTOMATIC SYSTEMS, SEPARATE

SCOPE IS PROVIDED, WHERE THE VIDEO IS PROCESSED

IN NORMAL (ANALOG) WAY.

• BY MONITORING THIS SCOPE THE OPERATOR CAN

ALWAYS FIND OUT PRESENCE OF JAMMING. THEN HE

CAN TAKE NECESSARY ACTION TO COUNTER IT. THIS

SCOPE IS CALLED RAW VIDEO SCOPE.

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PULSE INTEGRATION

• IF THE SIGNALS-TO–NOISE RATIO IS HIGH, THE AMPLITUDES OF THE

SIGNAL PULSES WILL GENERALLY BE GREATER THAN THOSE OF

THE NOISE PULSE.

• IF THE SIGNAL–TO-NOISE RATIO IS LOW A SINGLE PULSE IS

VIRTUALLY INDISTINGUISHABLE FROM A SINGLE NOISE PULSE AND

SO TARGET DETECTION BASED ON A SINGLE TARGET PULSE IS

IMPOSSIBLE.

• AS THE RADAR ANTENNA PATTERN SWEEPS PAST A TARGET

SEVERAL RADAR PULSES WILL BE REFLECTED WITHIN THE TIME

THE RADAR BEAM SWEEPS THE TARGET KNOWN AS DWELL TIME.

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• INSTEAD OF CONSIDERING EACH PULSE SEPARATELY

TO DECIDE WHETHER A TARGET IS PRESENT, A

NUMBER OF PULSES CAN BE ADDED TOGETHER AND

THE DECISION MADE ON THE BASIS OF THE SUM. THIS

PROCESS, CALLED INTEGRATION, CONSIDERABLY

IMPROVES THE ACCURACY OF THE DECISION.

• NOISE IS A RANDOM PHENOMENON WHEREAS AN

ECHO SIGNAL IS NOT. THEREFORE THE SUM OF A

NUMBER OF PULSES CONSISTING OF NOISE ALONE

WILL BE CONSIDERABLY DIFFERENT FROM THE SUM

OF A NUMBER OF PULSES CONTAINING A SIGNAL

PLUS NOISE.

PULSE INTEGRATION

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MOVING TARGET INDICATOR (MTI)

• THIS IS AN ANTI CLUTTER TECHNIQUE THAT LIMITS THE

DISPLAY TO INDICATE ONLY THE MOVING TARGET.

• THE TECHNIQUE DISCRIMINATES THE MOVING TARGETS FROM

A BACKGROUND OF CLUTTER OR STATIONARY CHAFF

PARTICLES BY USUALLY RECOGNIZING THE FREQUENCY

DOPPLER SHIFT.

• WHEN A TARGET MOVES WITH RESPECT TO THE RADAR

TRANSMITTER, THE REFLECTED SIGNAL RECEIVES A

FREQUENCY (PHASE) SHIFT PROPORTIONAL TO VELOCITY.

• AT MICROWAVE FREQUENCIES AND FIGHTER AIRSPEEDS THE

DOPPLER SHIFT IS UP TO 20 KHZ. RADARS CAN USE THIS

FREQUENCY/PHASE SHIFT AS AN EXCELLENT TRACKING

METHOD AND ECCM.

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MOVING TARGET INDICATOR (MTI)

• THE PERIOD (WAVELENGTH) OF 20 KHZ IS 200 MICROSECONDS.

• TO RECOVER THIS 20 KHZ SHIFT FROM THE ORIGINAL RADAR SIGNAL, THE ORIGINAL MUST BE CW OR A PULSE TRAIN WITH PULSES OF A PERIOD SEVERAL TIMES LONGER THAN 200 MICROSECONDS (A "PULSE DOPPLER" RADAR).

• SYSTEMS WHICH RECOVER THE SHIFT AS A DISCRETE FREQUENCY ARE CALLED DOPPLER RADARS WHILE THOSE CIRCUITS WHICH ONLY MEASURE PULSE-TO-PULSE FREQUENCY/PHASE DIFFERENCES ARE CALLED MOVING TARGET INDICATORS (MTI).

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Moving Target Indicator (MTI)

• MTI USES A PHASE DETECTOR TO PROVIDE ZERO AMPLITUDE (NO INPUT) SIGNALS TO THE TRACKING COMPUTER AND DISPLAY SCREENS FROM FIXED TARGETS SUCH AS WEATHER AND GROUND RETURN.

• ANOTHER METHOD OF MTI IS TO COMPARE THE TARGET LOCATION ON A PULSE-TO-PULSE BASIS. IF THE TARGET RETURN OCCURS AT EXACTLY THE SAME TIME (RANGE) ON TWO OR MORE SUCCESSIVE PULSES, IT DID NOT MOVE AND HENCE IS NOT APPLIED TO THE COMPUTER AND DISPLAY SCREEN. HERE IT IS PRIMARILY USED TO ELIMINATE CLUTTER.

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MOVING TARGET INDICATOR (MTI)

• TO ACHIEVE THIS THE BIPOLAR VIDEO SIGNAL IS FED INTO A DELAY

CHANNEL WHICH PROVIDES A TIME DELAY EQUAL TO ONE PULSE

REPETITION INTERVAL (PRI).

• THE OUTPUT OF THE DELAY CHANNEL IS SUBTRACTED FROM THE UN-

DELAYED SIGNAL. THE FIXED TARGET WITH UNCHANGING

AMPLITUDES FROM PULSE TO PULSE ARE CANCELLED ON

SUBTRACTION. FOR MOVING TARGETS THE OUTPUT OF THE

SUBTRACTION IS STILL A BIPOLAR VIDEO.

• THE PROBLEM WITH OLD MTI WAS THAT WHENEVER THE CHAFF HAS

SOME SPEED, IT COULD NOT BE REJECTED FULLY. NOW DIGITAL

MTIS HAVE ADOPTIVE CIRCUIT, WHICH CAN SHIFT THE NULL OF THE

CHARACTERISTIC TO ANY CLUTTER OR CHAFF SPEED SO AS TO

REJECT IT.

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Moving Target Indicator (MTI)

Undelayed bipolar video

Delay – line PRI

Subtractor

Full-wave rectifier

Video amplifier

From the phase detector

Delayed bipolar video

To video display

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SENSITIVITY TIME CONSTANT (STC)

• THIS IS A METHOD OF VARYING THE GAIN OF THE RADAR

RECEIVER DURING THE PRI TO PREVENT OVER LOADING OF THE

RECEIVER FROM NEARBY TARGETS AND SURFACE CLUTTER

RETURNS. THE RECEIVER GAIN STARTS OUT LOW AT NEAR

RANGES AND INCREASES TO MAXIMUM AT FAR OUT RANGES.

Fig. 5. Sensitivity Time Control

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LEADING EDGE TRACKING

• USED IN PULSED RANGE TRACKING RADAR TO DEGRADE THE

EFFECT OF RGPO TECHNIQUE

• IT ALLOWS TO DISCRIMINATE BETWEEN THE TRUE ECHO

SIGNAL AND THE SOMEWHAT DELAYED ECM SIGNAL.

• THE LEADING EDGE TRACKING (LET) CIRCUITS ALLOW TO

TRACK THE LEADING EDGE OF THE VIDEO ECHO PULSE

WHEREAS THE CONVENTIONAL RANGE TRACKER USES EARLY

GATE/ LATE GATE TO PERFORM TRACKING.

• A DECEPTION JAMMER GENERATES A FALSE ECHO DELAYED

FROM THE TARGET ECHO BY A FEW TENS OF NANOSECONDS

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Leading Edge Tracking

• ONCE THE RADAR AGC IS CAPTURED, CONVENTIONAL RANGE

TRACKING CIRCUIT WILL BE STOLEN BY THE FALSE ECHO.

• IN THE CASE OF LEADING TRACKING, THE VIDEO PULSE IS

DIFFERENTIATED.

• TWO VERY SHORT PULSES ARE OBTAINED AT TIMES

CORRESPONDING TO

– LEADING EDGES OF THE TARGET PULSE

– LEADING EDGE OF THE FALSE ECHO SIGNAL.

• THE FIRST LEADING EDGE PULSE IS THEN TRACKED WITH A SPLIT

GATE JUST LARGE ENOUGH TO ENCOMPASS ITS SHORT DURATION.

• THE LEADING EDGE OF THE FALSE ECHO SIGNAL IS THEREFORE

IGNORED.

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Leading Edge Tracking

P

t

P

t

P

t

P

t

Fig. 6 a-video signal

Fig. 6 b-leading edge differentiated pulses

Fig. 6 c-early and late LET gate (split gates)

Fig. 6 d-Leading Edge Tracking gate LET gate

LET tracking gate

Pulse from RGWOTarget pulse

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LOGARITHMIC AMPLIFIER

•A LOG AMPLIFIER IS AN AMPLIFIER, THE GAIN OF WHICH IS

PROPORTIONAL TO THE LOG OF THE INPUT SIGNAL.

•THIS RECEIVER HAS DYNAMIC RANGE OF THE ORDER OF 60 DB

AS COMPARED TO 10 TO 15 DB OF A NORMAL RECEIVER.

•IT IS VERY USEFUL TO AVOID SATURATION OF THE RECEIVER.

•THIS RECEIVER CONSISTS OF NUMBER OF IF AMP AND

DETECTOR STAGES. CURRENT OUTPUT OF EACH STAGE IS

ADDED IN PROPER WAY TO GIVE COMBINED OUTPUT, WHICH IS

PROPORTIONAL TO THE LOG OF INPUT. AS THE INPUT SIGNAL

INCREASES IN AMPLITUDE, SOME STAGES OF THIS RECEIVER

START GETTING SATURATED DUE TO WHICH OVERALL GAIN FOR

STRONGER SIGNALS IS REDUCED.

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LOGARITHMIC RECEIVERCOMPARISON WITH LINEAR

RECEIVER

Pout

Pinlinear receiver

saturation pointlog receiver

saturation point

linear receivercharacteristic

log receivercharacteristic

40 to 50 dB

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PULSE WIDTH DISCRIMINATOR

• THIS CIRCUIT CAN ELIMINATE ANY PULSE TYPE

INTERFERENCE WHICH IS NOT OF THE SAME LENGTH

AS THE TRANSMITTED PULSE.

• IT IS THEREFORE, USEFUL FOR REDUCING CLUTTER,

SLOW SWEEP NOISE JAMMING OR DECEPTION

JAMMING WITH DIFFERENT PULSE WIDTH.

• ALL THE PULSES RECEIVED ARE DIFFERENTIATED IN

A DIFFERENTIATING CIRCUIT. THIS CREATES A +VE

AND –VE SPIKE.

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PULSE WIDTH DISCRIMINATOR

• DIFFERENTIATED OUTPUT IS NOW FED TO TWO CHANNELS.

•ONE CHANNEL DELAYS IT BY PW OF THE RADAR, THE

OTHER ONE INVERTS IT. IF THE RECEIVED PULSE IS

OF CORRECT WIDTH, TWO +VE SPIKES AT THE OUTPUT

OF THIS CIRCUIT COINCIDE AND ARE ALLOWED TO

TRIGGER A COINCIDENCE CIRCUIT. OTHERWISE THE

PULSE WHICH IS FROM THE JAMMER IS REJECTED.

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DIFFEREN-TIATOR DELAYt

a b

ce

d

a

b

c

d

e

Am

p

TIME

r

t t

COINCIDENCEAMP

INVERTOR

Fig. 8.Block Diagram and Pulse Output of a PLD Circuit

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•PURPOSE OF THIS ECCM IS TO DEGRADE THE EFFECTS OF NOISE JAMMING, CHAFF AND CLUTTER IN THE RADAR RECEIVER.

• IT IS A FAST AGC TECHNIQUE THAT USES THE NOISE SIGNAL JUST BEFORE AND AFTER THE SIGNAL PULSE IN ORDER TO CONTROL THE GAIN OF AN IF AMPLIFIER.

•THIS TECHNIQUE IS MORE SUITABLE TO A TRACKING RADAR THAN TO A SEARCH BECAUSE IT ASSUMES THAT TARGET HAS ALREADY BEEN DETECTED.

INSTANT GAIN CONTROL

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•THE CIRCUIT IS DESIGNED TO OPERATE AGAINST OFF-

FREQUENCY INTERFERENCE THAT IS INTENSE ENOUGH FOR

THE SPECTRAL SIDE BANDS OF THE SIGNAL TO INTERFERE

WITH NORMAL RADAR RECEPTION.

•THE WIDE BAND AMPLIFIER IS DESIGNED TO ACCEPT MOST

OF THE INTERFERING SPECTRUM. AFTER LIMITING, IF BOTH

SIGNALS ARE NOT PRESENT SIMULTANEOUSLY AND IF THE

LEVEL IS ABOVE THE AMPLITUDE OF THE DESIRED PULSE, THE

AMPLITUDE OF THE INTERFERING PULSE IS REDUCED RELATIVE

TO THE RADAR SIGNAL AND THEREFORE ITS SIDE BANDS ARE

REDUCED TO TOLERABLE LEVELS.

DICKE-FIX

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DICKE-FIX RECEIVER

t

IF

wide band,Bw

IFwideband

limiterA B C

narrow bandmatched,Bn

P

pointA

t

P

pointB

t

P

pointC

J

J

J

S

S

S

a-dicke-fix basic block diagram

b-waveforms

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RANGE GUARD GATE

GA t

P

GA t

P

A t

P

A t

P

GA t

P

S

J

S

S

S

SJ

a-benign situation

b-AGC capture

c-tracking gate capture

d-guard gate detection

e-tracking gate repositioning

J

G

J

G

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VELOCITY GUARD GATES

GA

P

GA f

P

P

P

P

S

J

S

a-benign situation

b-AGC capture

c-tracking gate capture

d-guard gate detection

e-tracking gate repositioning

B

GA B

GA B

G BA

B

f

f

f

f

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FAST TIME CONSTANT

R

S

R

S

targetpulse

wide ECMor

clutter pulse

targetpulse

edges of wide pulse

a-video without FTC

b-video with FTC

PPI without FTC

PPI with FTC

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• HIGH ANTENNA GAIN• HIGH DIRECTIVITY• SIDE LOBE BLANKING/

SUPPRESSION• POLARIZATION AGILITY• CONTROL OF RECEIVING BEAM PATTERN• MULTI-BEAM ANTENNA• LOBE ON RECEIVE ONLY (LORO)• CONICAL SCAN ON RECEIVE ONLY

(COSRO)

ANTENNA RELATED ECCM

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SIDE LOBE REDUCTION

• STAND OFF JAMMER EMPLOYS HIGH POWER NOISE JAMMING PENETRATING THROUGH THE RADAR SIDE LOBES.

• FALSE TARGET GENERATORS CAN ALSO INTRODUCE FALSE ECHO THROUGH THE SIDE LOBES.

• ON TRANSMIT, THE ENERGY RADIATED THROUGH THE SIDE LOBES IS SUBJECT TO BE DETECTED BY ENEMY INTERCEPT SYSTEM OF ARMS.

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SIDE LOBE REDUCTION

• FOR A GIVEN ANTENNA GAIN, SIDE LOBES REDUCTION MEANS THAT A LARGER ANTENNA APERTURE IS NEEDED.

• CONVERSELY, FOR A GIVEN SIZE OF ANTENNA, LOWER SIDE LOBES MEANS LESS GAIN AND A CORRESPONDINGLY BROADER BEAM WIDTH.

• IN ORDER TO KEEP THE BEAM WIDTH SMALL WITH LOW SIDE LOBES, A LARGER AND MORE COSTLY ANTENNA IS NEEDED.

• OTHER DESIGN PRINCIPLES INVOLVED IN LOW ANTENNA SIDE

LOBES ARE THE USE OF RADAR OBSERVANT MATERIAL (RAM)

ABOUT THE ANTENNA STRUCTURE, THE USE OF A FENCE ON

GROUND INSTALLATIONS, AND THE USE OF POLARIZATION

SCREENS AND REFLECTORS.

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SIDE LOBE BLANKING

• THIS TECHNIQUE PREVENTS SOME OF THE UNWANTED PULSE ENERGY THAT

ENTERS THE SIDE LOBE OF A RADAR ANTENNA FROM ADVERSELY AFFECTING

THE RADARS OPERATION.

• SLB CAN BE USED ON SEARCH RADARS, TRACKING RADARS AND IN MISSILE

GUIDANCE SYSTEMS.

• THE SLB SYSTEM EMPLOYS AN AUXILIARY OMNI-DIRECTIONAL ANTENNA

COUPLED WITH AS AUXILIARY RECEIVING CHANNEL, SO THAT TWO SIGNALS FROM

A SINGLE SOURCE ARE AVAILABLE FOR COMPARISON. BY CHOOSING THE

AUXILIARY ANTENNA GAIN SLIGHTLY HIGHER THAT THE A MAIN ANTENNA SIDE

LOBE GAIN, SIGNALS ENTERING THE SIDE LOBES CAN BE DISTINGUISHED FROM

THOSE AFFECTING THE MAIN BEAM. THE JAMMING SIGNALS AFFECTING THE SIDE

LOBES CAN THEREFORE BE SUPPRESSED

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SIDELOBE BLANKING

-20° +20°0

main antenna pattern

auxiliary sidelobeblanking antennapattern

degrees offmainbeam axis

P

antenna patterns

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LO

IF

IF

Detector

High pass filter

Amplitude comparator

High – pass filter

Gate

Gate driver

detector

Main antennaRadar video

Auxiliary antenna

Side lobe blanking

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POLARISATION CANCELLER

• THE POLARIZATION CANCELLER ECCM TECHNIQUE IS USED TO DEGRADE THE EFFECTIVENESS OF CIRCULARLY POLARIZED JAMMING. IT HAS SAME ACTION AGAINST ELLIPTICAL OR SLANT POLARIZED JAMMING SIGNALS.

• IT CAN BE IMPLEMENTED ON SEARCH OR TRACKING PULSED RADARS.

• POLARIZATION CANCELLER TECHNIQUE IS BASED ON THE PRINCIPLE THAT THE POLARIZATION COMPONENTS OF A SINGLE JAMMING SIGNAL CAN BE CORRELATED BECAUSE BOTH OF THEM COME FROM THE SAME POINT, WHEREAS THE POLARIZATION COMPONENTS OF A REFLECTED TARGET SIGNAL ARE NOT GENERALLY IN-PHASE AND WILL NOT BE CORRELATED.

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POLARISATION CANCELLER

• THIS IS DUE TO THE FACT THAT AN ACTUAL TARGET IS A COMPLEX SCATTERER, REFLECTING TO THE RADAR RECEIVER A COMPLEX AND FLUCTUATING SIGNAL. THE CORRELATION BETWEEN THE TWO COMPONENTS OF A SINGLE POINT NOISE JAMMING SIGNAL ALLOWS TO CANCEL IT BY SOME AMOUNT.

• THE BASIC IMPLEMENTATION OF A POLARIZATION CANCELLER, USES AN ADDITIONAL CHANNEL IN THE RADAR RECEIVER WHICH MATCHES AMPLITUDE AND TIME DELAY WITH THE MAIN RADAR RECEIVER CHANNEL. THE MAIN CHANNEL AND THE AUXILIARY CHANNEL ARE EQUIPPED WITH CROSS- POLARIZED ANTENNAS.

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POLARISATION CANCELLER

• IF NO JAMMING SIGNAL IS DETECTED, THE RADAR OPERATES WITH HORIZONTAL POLARIZATION ON THE MAIN CHANNEL.

• WHEN A CIRCULARLY POLARIZED NOISE JAMMING IS DETECTED, THE POLARIZATION CANCELLER IS ACTIVATED AND TWO CHANNELS ARE USED.

• THE CIRCULARLY POLARIZED JAMMING SIGNAL PRESENTS TWO COMPONENTS, WHICH WILL BE DETECTED IN THE MAIN AND AUXILIARY CHANNELS.

• SINCE THE VERTICAL AND HORIZONTAL COMPONENTS OF THE CIRCULARLY POLARIZED JAMMING SIGNAL ARE SELDOM PERFECTLY OF EQUAL AMPLITUDE, LOGARITHMIC AMPLIFIERS ARE NECESSARY. THEY NORMALIZE ANY DIFFERENCE IN AMPLITUDE OF THE INPUT SIGNALS.

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POLARISATION CANCELLER

• REGARDLESS OF THE AMPLITUDE OF A NOISE –MODULATED INPUT

SIGNAL TO A LOGARITHMIC AMPLIFIER, THE INPUT SIGNAL AMPLITUDE

MODULATION WILL APPEAR AT THE OUTPUT WITH THE SAME

AMPLITUDE DEVIATION.

• THE OUTPUT SIGNAL OF THE LOG –AMPLIFIER DETECTOR IS AC

COUPLED SO THE ONLY THE NOISE MODULATION IS ALLOWED TO

PASS, THE DC COMPONENT OF THE JAMMING BEING FILTERED OUT.

• THE TWO DETECTED COMPONENTS OF THE JAMMING SIGNAL ARE

THEREFORE EQUAL IN AMPLITUDE AND CAN BE CANCELLED WITH THE

VIDEO CANCELLER. THE CROSS POLARIZED TARGET-SKIN RETURN

WILL BE OF RANDOM AMPLITUDE AND PHASE WITH RESPECT TO THE

CO-POLARIZED TARGET SKIN RETURN AND WILL HAVE LITTLE

CANCELLATION EFFECT UPON THE CO-POLARIZED ECHO SIGNAL.

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Amplitude and time matching

Logarithmic amplitude detector

Duplexer

Radar transmitter

Video canceller

Bipolar detector

Logarithmic amplitude detector

Amplitude and time matching

Main channel

LO

Video output

Horizontal polarisation

Vertical polarisation

Auxiliary channel

Block diagram of Polarization cancellation circuit

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LOBE-ON-RECEIVE ONLY (LORO)

• IN THIS TECHNIQUE, THE TRACKING RADARS SO THAT THE

TRANSMISSION IS ON A FIXED BEAM ALIGNED WITH THE BORE-

SIGHT. THE RECEIVING ANTENNA HOWEVER SCANS AROUND

THE BORE-SIGHT.

• THE ECHO SIGNALS, THEREFORE, DO GET AMPLITUDE

MODULATED. HOWEVER, THE ECM EQUIPMENT ON BOARD

ALWAYS RECEIVES CW SIGNALS WITHOUT ANY MODULATION.

• TRANSMITTING WITH INVERSE MODULATION IS THEREFORE NOT

POSSIBLE FOR THE ECM EQUIPMENT.

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CONICAL SCAN ON RECEIVER ONLY (COSRO)

• THE PRINCIPLE OF THE CONICAL SCAN ON RECEIVE

ONLY (COSRO) TECHNIQUE IS TO PERFORM THE

CONICAL SCANNING NECESSARY FOR ANGLE

TRACKING ON RECEIVE ONLY. THE TRANSMIT BEAM

REMAINS POINTED AT THE TARGET, PRODUCING AN

UN-MODULATED RF PULSE TRAIN AT THE TARGET.

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POLARIZATION SCREENS AND REFLECTORSPRINCIPLE

a. polarization screen for vertically polarized radar signal

b. polarization reflector for vertically polarized radar signal

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NARROW ANTENNA BEAM

• ANOTHER METHOD WHICH IS EMPLOYED TO REDUCE

THE EFFECT OF MAIN BEAM NOISE JAMMING IS TO

RAISE THE TRANSMITTER FREQUENCY IN ORDER TO

NARROW THE ANTENNA’S BEAMWIDTH.

• THIS RESTRICTS THE SECTORS WHICH IS BLANKED

BY MAIN LOBE NOISE JAMMING AND ALSO PROVIDES

A STROBE IN THE DIRECTION OF THE JAMMER.

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STACKED BEAM• IN A STACKED BEAM RADAR, SEVERAL SIMULTANEOUS

OVERLAPPING BEAMS ARE FORMED, EACH AT A DIFFERENT

ANGLE OF ELEVATION.

• EACH BEAM IS TRANSMITTED AT A DIFFERENT FREQUENCY SO

THAT MUTUAL INTERFERENCE BETWEEN BEAMS IS REDUCED

AND THE TARGET AMPLITUDE IN ADJACENT BEAMS CAN BE

COMPARED.

• EACH BEAM FEEDS A SEPARATE RECEIVER AND TARGET

ELEVATION ANGLE IS OBTAINED BY BEAM COMPARISON

Stacked Beams


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