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1 SINGLE TGT TRACKER (STT) TRACKS A SINGLE TGT AT FAST DATA
RATE.
DATA RATE 10 OBS/SEC. EMPLOYS A CLOSED LOOP SERVO SYSTEM
TO KEEP THE ERROR SIGNAL SMALL.
MISSILE TGTS
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(ADT)
SURVEILLANCE TRACKING RADAR. .
CAN TRACK HUNDREDS/ A FEW
THOUSAND TGTSSIMULTANEOUSLY.
TRACKING IS OPEN LOOP.
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ELECTRONICALLY STEERED PHASED
. LARGE NO OF TGTS CAN BE HELD
ON TRACK.
HIGH DATA RATE (LIKE IN STT)
BEAM IS ELECTRONICALLY
POSITION TO ANOTHER IN A FEW
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SCANS A LIMITED ANGULAR SECTOR TO MAINTAIN
TRACKS SIMULTANEOUS TRACK & SEARCH
DATA RATE : MODERATE
CAN TRACK A NUMBER OF TARGETS.
EQUIVALENT OF TRACK WHILE SCAN IS ADT :
ANGULAR SECTOR, USUALLY IN BOTH AZIMITH &ELEVATION.
,NARROW BEAMWIDTH PENCIL BEAM; OR WITH TWOORTHOGNAL FAN BEAMS (ONE FOR AZIMUTH AND
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AMPLITUDES GIVES THE LOCATION OF THETGT WRT ANT. AXIS.
THE AMPLITUDE AND THE SENSE OF ERRORSIGNAL CAN BE USED TO GENERATE THECORRECTIVE SIGNAL WHICH WITH THE
HELP OF SERVO CONTROL CAN BE USED TO
TARGET ON THE ANTENNA AXIS.
WHEN TGT X-SECTION CHANGES BETWEEN
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TRACKING & RADAR BLOCK DIAGRAM
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SIGN OF O/P OF PHASE SENSITIVEDETECTOR INDICATES THE DIRECTION OFTHE ANGLE ERROR RELATIVE TO THE
.
ANGLE ERROR ; MAGNITUDE IS
PATTERN.
SIGNAL.
FOR DETERMINING THE SIGN OF THEANGLE MEASUREMENT.
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ANGLE TRACKING
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ANGLE TRACKING
BEAM SHOULD BE MOVED TO THE RIGHTTO COINCIDE BORESIGHT & TGT
.
BORESIGHT POSITION 0 IS LOCATED INTHE DIRECTION OF THE TARGET.
THE ABOVE TWO BEAMS ARE SAID TO BE
SQUINTED WITH A SQUINT ANGLE.
BORESIGHT DIRECTION : CROSSOVER OF 2
. AIM IS TO POSITION THE 2 BEAMS SO
THAT = TGT ON THE BORESIGHT
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HYBRID JUNCTIONS
OPERATION DEPENDS ON LENGTHS BETWEEN PORTS AND
HENCE THE DEVICE IS FREQ. SENSITIVE
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TWO COORDINATE MTR (AMP COMPARISON)
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SUM PATTERN : A+B +C +D
AZIMUTH DIFF. PATTERN : (A+B) (C +D)ELEVATION DIFF. PATTERN : (B+D) (A+C)
AGC ENSURES THAT ANGLE ERRORSIGNAL IS NOT EFFECTED BY CHANGESIN SIG. AMPLITUDE.
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LIMITATIONS TO TRACKING ACCURACY
GLINT/ANGLE NOISE/TGT NOISE
RECEIVER NOISE
AMPLITUDE FLUCTUATIONS OF TGT ECHO
OTHERS (MECH PROPERTIES OF ANT,
SERVO SYSTEM ETC) GLINT OCCURS WITH COMPLEX TGTS
WHICH HAVE MORE THAN ONE
ECHOS FROM MULTIPLE SCATTERERS
DIFF. WAVE TILTS.
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GLINT FROM A COMPLEX TGT CAUSES
;RESULTING IN AN ERROR IN THE
GLINT SOMETIMES CAN CAUSE BREAK.
BREAK- TRACK OCCURS WHEN THE
BORESIGHT OF THE TRACKINGANTENNA POINTS OUTSIDE THEANGULAR EXTENT OF THE TARGET.
GLINT IS A MAJOR SOURCE OF ERROR,WHEN MAKING ANGLE MEASUREMENTS,ESPECIALLY AT SHORT RANGES.
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CONICA SCAN (CON - SCAN) & SEQUENTIALLOBING A SINGLE ANTENNA BEAM IS TIME SHARED TO OBTAIN
TIME SHARING A SINGLE ANT. BEAM IS SIMPLER ,USES LESSEQPT THAN SIMULTANEOUS BEAMS BUT IT IS NOT AS
.
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SQUINT ANGLE IT IS THE ANGLEBETWEEN THE AXIS OF ROTATION AND
A TARGET LOCATION
SINCE THE TARGET IS OFFSET FROM THE,CAUSES MODULATION OF THE AMP. OF
TO BEAM ROTATION FREQ.(CONICALSCAN FREQ)
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CONICAL SCAN TRACKING RADAR
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TYPICAL CONICAL SCAN
REV/SEC
THE PLANE OF POLARISATION ROTATING FEED IT CAUSES THE
PLANE OF POLARISATION TO
ROTATE. NUTATING FEED IS PREFERED !!
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COSRO CONICAL SCAN ON
MILITARY CONICAL SCAN AND LOBE
SWITCHING TRACKING RADARS AREVULNERABLE TO ECM, SINCE CONICAL.
A HOSTILE ECM JAMMER CAN DISRUPTCONICAL SCAN TRACKING OF RADAR
RADAR SIGNAL WITH AN AMP.MODULATION THAT IS THE INVERSE OF
.
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COUNTERMEASURE ISCALLED INVERSE GAIN
CONICAL SCAN TRACKING
TRACKING SYSTEMS
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CONICAL SCAN FREQ BY ECM JAMMER) TRACKING RADAR ILLUMINATES THE
TARGET WITH NON SCANING BEAM
AND APPLY CONICAL SCANNING ONRECEIVE ONLY
HENCE THE NAME COSRO
ANALOGOUS OPERATION WITHSEQUENTIAL LOBING IS CALLED LORO
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CONICAL SCAN SEQUENTIAL LOBING.
LOBE SWITCHING ANTENNA PATTERNS
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CONICAL SCAN CONTDTHE DIFFERENCE IN AMPLITUDE BETWEEN
THE VOLTAGES OBTAINED IN THE TWO
SWITCHED POSITIONS IS A MEASURE OFANGULAR DISPLACEMENT OF THE TGTFROM THE SWITCHING AXIS.
THE DIRECTION IN WHICH TO MOVE THE
SIGHT IS FOUND BY OBSERVING WHICH
SIGNAL.
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PULSES BEFORE LOW PASS
THE ENERGY AT THE CONICAL
ANALOG TO DIGITAL CONVERSION.
THIS PULSE STRETCHING IS DONE.
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COMPARED WITH CONICAL SCAN FREQFOR PROPER FILTERING AND AVOIDINGINACCURACY OF THE ANGLE
MEASUREMENT THERE MUST BE ATLEAST 4 PULSES
DURING EACH REVOLUTION OF THE
OBTAIN UP DOWN AND RIGHT-LEFT
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TIMES THAT OF CONICALSCAN FREQUENCY; BUT IT IS
MORE THAN 10 TIMES
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COMPARISON TRACKERS 1. S/N RATIO- IT IS GREATER IN
MONOPULSE RADAR THAN IN CONICAL
SCAN RADAR IT IS BECAUSE IN MONOPULSE,
ANTENNA VIEWS TARGET AT THE PEAK
OF ITS SUM PATTERN. CONICAL SCAN RADAR VIEWS THE TGT
AT SOME ANGLE OFF THE PEAK OF THE
.
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.
MONOPULSE (DUE TO 1) IN
3. COMPLEXIT Y : MONOPULSERADAR IS MORE COMPLEX, DUE
AT THE ANTENNA & 3
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. COMPARISON TRACKERS (contd )
CONICAL SCAN RADAR HAS ONLY ONERECEIVING CHANNEL & USES A SINGLE
.
HOWEVER, DUE TO SOLID STATE AND,
SELDOM A REASON FOR NOT CHOOSING
MONOPLUSE. 4. MINIMUM NO OF PULSES : MONOPULSE
SINGLE PULSE
MINIMUM OF 4 PULSES PER REVOLUTIONOF THE BEAM TO EXTRACT AN ANGLEMEASURMENT IN TWO COORDINATES.
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.
MEASUREMENT AND THEN
MEASUREMENTS TO OBTAIN THE
CONICAL SCAN RADAR, INTEGRATES
,THEN EXTRACTS THE ANGLE
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COMPARISION TRACKERS (CONTD)
.
6 . SUSCEPTIBILITY TO ECM
CONICAL SCAN RADAR IS MORESUSCEPTIBLE TO ECM,
A WELL DESIGNED MONOPULSETRACKER IS MUCH HARD TO DECEIVE.
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-
MONOPULSE TRACKERS ARE USED WHENGOOD ANGLE ACCURACY IS RE UIREDAND
WHEN SUSCEPTIBILITY TO ECM IS TO BEMINIMISED.
APPLICATION CONICAL SCAN
TRACKER IT IS USED BECAUSE OF LOWER COST AND
REDUCED COMPLEXITY.
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MANUAL TRACKING OF
REPLACED BY CLOSED LOOPAUTOMATIC TRACKING,
TRACKER.
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TRACKING IN RANGE
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TRACKING IN RANGE ( CONTD )
LESS THAN THAT OF THE LATE GATE.
THE SIGNALS IN THE TWO GATES ARE
SUBTRACTED TO PRODUCE THE DIFFERENCEERROR SIGNAL
.FAR THE PAIR OF GATES ARE FROM THE
.
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AUTOMATC GAIN CONTROL
: ERROR SENSITIVITY IN SPITE OFAMPLITUDE FLUCTUATIONS OR CHANGES
RANGE AGC SIGNALNEGATIVE DC VOLTAGE
VOLTAGE
CONSTANT ANGLE ERROR SENSITIVITYPROVIDES STABLE TRACKING. AGC AVOIDS SATURATION BY LARGE
SIGNALS
AGC ALSO ATTEMPTS TO REMOVE THE NOISE LIKE AMPLITUDE OF THE TGT ECHO
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AGC (contd)
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AGC (contd)
HOWEVER THE GAIN OF THE AGC
AS TO SUPPPRESS THE ERROR.
THE REQUIRED DYNAMIC RANGE
VARIATION IN RANGE OVER WHICH
EXPECTED VARIATION IN TGT..
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EX : RANGE VARIATION = 40 DB
VARIATION = 40 DB
PARAMETERS = 10 DB
DYNAMIC RANGE (FOR RX AGC)= 90 DB
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A TRACKING RADAR MUST
TARGET BEFORE IT CANOPERATE AS A TRACKER.
CARE TO COVER THE ENTIRE
EFFICIENTLY.
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g a
ANTEENA ISCONTINOUSLY ROTATED
LOWERED IN ELEVATION.
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IT CONSISTS IN RAPID CIRCULAR
AXIS OF THE ANTEENA, COMBINED
THE AXIS OF ROTATION. IT IS
LARGER IN ONE DIMENSION THANANOTHER.
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SPIRAL SCAN (Fig c) :
THIS SCAN COVERS AN ANGULAR SEARCHVOLUME WITH CIRCULAR SYMMETRY.
BOTH SPIRAL SCAN & PALMER SCANSUFFER FROM THE DISADVANTAGE THATALL PARTS OF THE SCAN VOLUME DO
SCANNING SPEED IS VARIED DURING THE.
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IN A UNIFORM MANNER. IT IS A CONVENIENT MEANS
SECTOR, RECTANGULAR IN.
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NODDING SCAN (Fig e) IT IS PRODUCED BY OSCILLATING THE
ANTEENA BEAM RAPIDLY IN ELEVATION.
IT IS USED TO COVER A LIMITED SECTOR
OBTAIN A HEMISPHERICAL COVERAGEELEVATION ANGLE UP TO 900 AND
AZIMUTH SCAN ANGLE UPTO 3600 )
USED IN HEIGHT FINDING RADARS.