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8/7/2019 RadarFundamentals
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RADAR SYSTEMS
Presented by
Al Scottof
Besser Associates, Inc.
www.BesserAssociates.com
Sponsored by
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COURSE OUTLINE
• How radar works
•
Measurement of target range and velocity• Measurement of angle
• Antennas
• Electronically Steered Array antennas (ESA)
•
Synthetic Aperture Antennas (SAR)
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RADAR FREQUENCY BANDS
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MAJOR TECHNOLOGY ADVANCEIN RADAR IN THE LAST 15 YEARS
Signal processing required for new radar and EWtechniques is rapidly increasing.
Defined as MOPS = Million operations per second
Commercial Off The Shelf (COTS) computer chips
meet MOPs needs but won’t meet environmental
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RADAR VELOCITY MEASUREMENT
Reflected signal is shifted in frequency by velocityReflected signal is shifted in frequency by velocity of targetof target
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CALCULATION OF VELOCITY FROMDOPPLER FREQUENCY SHIFT
Velocity (MPH) =Velocity (MPH) = Doppler shift (Hz)____ Doppler shift (Hz)____
3.9 x RF frequency (GHz)3.9 x RF frequency (GHz)
Example:Example:
Doppler shift = 1 kHzDoppler shift = 1 kHzRF frequency = 10 GHzRF frequency = 10 GHz
Velocity = 1000 / 3.9 x 10 = 25.6 MPHVelocity = 1000 / 3.9 x 10 = 25.6 MPH
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SIMPLE DOPPLER RADAR
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CIRCULATOR
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RADAR RANGE MEASUREMENT
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CALCULATION OF RANGE FROMECHO DELAY TIME
Target range (feet) = 500 x Echo delay time (Target range (feet) = 500 x Echo delay time (microsecmicrosec))
Example:Example:
Echo delay time = 10Echo delay time = 10 microsecmicrosecTarget range = 500 x 10 = 5000 feetTarget range = 500 x 10 = 5000 feet
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A SCOPE PRESENTATION
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PULSE RADAR BLOCK DIAGRAM
TransmitterReceiver
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CLUTTER
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CLUTTER SUPPRESSION USING MTI
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PULSE DOPPLER RADAR
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VELOCITY AMBIGUITY
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RANGE AMBIGUITY
PRF for unambiguous range = 92 miles/PRF (kHz)
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RANGE-VELOCITY AMBIGUITY
TRADE OFF
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PRF SWITCHING
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RANGE RESOLUTION
Range resolution (feet) = 500 x pulse length (µµµµsec)
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PULSE COMPRESSION RADAR
Time length of compressed pulse (µµµµsec) = 1/RF frequency sweep (MHz)
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SURFACE ACOUSTIC WAVE
DELAY LINE
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RADAR ANGULAR MEASUREMENT
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REASON FOR POOR ANGULAR
RESOLUTION
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ANTENNA PROPERTIES
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TYPES OF PARABOLIC ANTENNAS
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TECHNIQUES TO IMPROVE
ANGULAR RESOLUTION
Larger antenna
Higher frequency
Tracking mode Radar closer to target (in missile)
Phased array radar
Synthetic aperture radar (SAR)
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BEAM MOVEMENT IN A
PARABOLIC DISH ANTENNA
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RADAR TRACKING MODE
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COMPARISON OF SEARCH AND
TRACKING ANTENNA BEAMS
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BEAM MOVEMENT IN A
PHASED ARRAY ANTENNA
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PHASED ARRAY ANTENNA
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T/R MODULE
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ADVANTAGES OF ESAs
Radar cross section (RCS) reduction
Extreme Beam Agility
• Beam placed anywhere with +/-60o cone in < 1 millisecond
• Tracking can be established the instant a target is detected
• Single target tracking accuracies obtained against
• multiple targets.
• Targets for missiles controlled by the radar can be trackedeven when they are outside the radar’s search volume.
• Dwell times can be individually optimized to meet detectionand tracking needs.
High Reliability
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SYNTHETIC APERTURE RADAR (SAR)
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RESOLUTION OF
SYNTHETIC APERTURE RADAR
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COMPARISON OF PHOTOGRAPH
TO SAR IMAGE
AerialAerial
photographphotograph
SAR image fromSAR image from
many timesmany timesgreater rangegreater range
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