RadarFundamentals

8/7/2019 RadarFundamentals

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1www.BesserAssociates.com

RADAR SYSTEMS

Presented by

Al Scottof

Besser Associates, Inc.

www.BesserAssociates.com

Sponsored by






















COURSE OUTLINE

• How radar works

•

Measurement of target range and velocity• Measurement of angle

• Antennas

• Electronically Steered Array antennas (ESA)

•

Synthetic Aperture Antennas (SAR)






RADAR FREQUENCY BANDS




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




RADAR VELOCITY MEASUREMENT

Reflected signal is shifted in frequency by velocityReflected signal is shifted in frequency by velocity of targetof target




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




SIMPLE DOPPLER RADAR




CIRCULATOR




RADAR RANGE MEASUREMENT




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




A SCOPE PRESENTATION




PULSE RADAR BLOCK DIAGRAM

TransmitterReceiver




CLUTTER




CLUTTER SUPPRESSION USING MTI




PULSE DOPPLER RADAR




VELOCITY AMBIGUITY




RANGE AMBIGUITY

PRF for unambiguous range = 92 miles/PRF (kHz)




RANGE-VELOCITY AMBIGUITY

TRADE OFF




PRF SWITCHING




RANGE RESOLUTION

Range resolution (feet) = 500 x pulse length (µµµµsec)




PULSE COMPRESSION RADAR

Time length of compressed pulse (µµµµsec) = 1/RF frequency sweep (MHz)




SURFACE ACOUSTIC WAVE

DELAY LINE




RADAR ANGULAR MEASUREMENT




REASON FOR POOR ANGULAR

RESOLUTION




ANTENNA PROPERTIES




TYPES OF PARABOLIC ANTENNAS




TECHNIQUES TO IMPROVE

ANGULAR RESOLUTION

Larger antenna

Higher frequency

Tracking mode Radar closer to target (in missile)

Phased array radar

Synthetic aperture radar (SAR)




BEAM MOVEMENT IN A

PARABOLIC DISH ANTENNA




RADAR TRACKING MODE




COMPARISON OF SEARCH AND

TRACKING ANTENNA BEAMS






BEAM MOVEMENT IN A

PHASED ARRAY ANTENNA




PHASED ARRAY ANTENNA






T/R MODULE




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




SYNTHETIC APERTURE RADAR (SAR)




RESOLUTION OF

SYNTHETIC APERTURE RADAR




COMPARISON OF PHOTOGRAPH

TO SAR IMAGE

AerialAerial

photographphotograph

SAR image fromSAR image from

many timesmany timesgreater rangegreater range



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RadarFundamentals