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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
50/119
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
51/119
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.
53/119
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
54/119
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.
55/119
LOGARITHMIC RECEIVERCOMPARISON WITH LINEAR
RECEIVER
Pout
Pinlinear receiver
saturation pointlog receiver
saturation point
linear receivercharacteristic
log receivercharacteristic
40 to 50 dB
56/119
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.
57/119
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.
58/119
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
59/119
•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
61/119
•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
62/119
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
63/119
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
65/119
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
66/119
• 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
67/119
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.
68/119
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.
69/119
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
70/119
SIDELOBE BLANKING
-20° +20°0
main antenna pattern
auxiliary sidelobeblanking antennapattern
degrees offmainbeam axis
P
antenna patterns
71/119
LO
IF
IF
Detector
High pass filter
Amplitude comparator
High – pass filter
Gate
Gate driver
detector
Main antennaRadar video
Auxiliary antenna
Side lobe blanking
75/119
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.
76/119
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.
77/119
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.
78/119
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.
79/119
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
80/119
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.
82/119
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.
84/119
POLARIZATION SCREENS AND REFLECTORSPRINCIPLE
a. polarization screen for vertically polarized radar signal
b. polarization reflector for vertically polarized radar signal
85/119
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.
86/119
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