Pulse Doppler Effect

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Pulse Doppler Effect

  1. 1. Pulse Doppler SpectrumByTariq Kanher
  2. 2. Pulse Doppler SpectrumPulse Doppler ClutterGround Clutter in Stationary RadarGround Clutter in Moving RadarSidelobe ClutterMain Beam ClutterSingle Target TrackingMultiple Target TrackingAgenda
  3. 3. Pulse Doppler Spectrum
  4. 4. Pulse Doppler Spectrum
  5. 5. Pulse Doppler Spectrum
  6. 6. Pulse Doppler Spectrum
  7. 7. previous figure show the unfolded spectrum in caseof horizental motion of radar, with a velocity VR .The clutter free region in define as that portion of thespectrum in which no ground clutter can exist.The side lobe clutter region, 4VR /λ in width, containsground clutter power from the side lobes of theantenna, although the clutter power may be belowthe noise level in part of the region.Pulse Doppler Spectrum
  8. 8. Altitude line clutter, which is due to ground clutter atnear normal incidence directly below the radarplatform, is at zero Doppler if there is no verticalcomponent of platform velocity.A discrete target return in the main beam is shown atfT = f0 + 2VR /λ cos (Ψo) + 2VT /λ cos (ΨT) ,where thetarget velocity is VT with an angle between the targetvelocity vector and radar target line of sight.Pulse Doppler Spectrum
  9. 9. The main beam region , located at f0 + 2VR /λ cos(Ψo)contains the strong return from the main beam ofantenna striking the ground at scan angle of Ψomeasured from the velocity vector.Rain and chaff clutter may also be large when themain beam illuminates a rain or chaff cloud. Motiondue to winds may displace and/or spread the return infrequency.Pulse Doppler Spectrum
  10. 10. Clutter returns from various scatters have a stronginfluence on the design of a pulse Doppler radar aswell as an effect on the probability of detection ofpoint targets.PULSE DOPPLER CLUTTER
  11. 11. When the radar is fixed with respect to theground, both main-beam and side lobe clutter returnsoccur at zero Doppler offset, the transmit frequency.The side lobe clutter is usually small compared withmain beam clutter.The clutter can be calculated as in a pulse radar, thenfolded in range as a function of the PRF.GROUND CLUTTER IN A STATIONARYRADAR
  12. 12. When the radar is moving with a velocity VR theclutter is spread over the frequency domain asillustrated in figure for special case of horizontalmotion.The fold over in range and Doppler is illustrated innext Fig for a medium-PRF radar where the clutter isambiguous in both range and Doppler.Ground Clutter in a Moving Radar
  13. 13. The radar platform is moving to the right at 1000kmwith a drive angle of 10 degree.The narrow annuli define the ground area thatcontributes to clutter in the selected range gate.The five narrow hyperbolic bands define the area thatcontributes to clutter.Ground Clutter in a Moving Radar
  14. 14. The entire clutter spectrum can be calculated for eachrange gate by Equation next slide, if the antennapattern is known in the lower hemisphere.In preliminary system design, the exact gain functionmay not be known, so that one useful approximationis that the side lobe radiation is isotropic with aconstant gain of GSL .Side lobe Clutter
  15. 15. The main-beam clutter-to-noise power can beapproximated from equationThe summation limits are the lower and upper edgesof the smaller of the transmit and receive beams.Main-Beam Clutter
  16. 16. Main-Beam Clutter
  17. 17. Tracking can be identical to a congenital pulse radarusing mono pulses, sequential lobbing or conical scan.Mono pulse is more difficult to mechanize because ofthe problem of phase and amplitude matching of themultiple receiver channels.Single-Target Tracking
  18. 18. Multiple target tracking can be accomplished inseveral ways.One, track while scan , is to use normal search modewith FM or multiple PRF ranging and store therange, angle and Doppler of the reported detection inthe computer.Multiple-Target Tracking
  19. 19. A second method of multiple-target tracking, pause-while-scan, particularly applicable to electronic scanantennas, is to scan in a normal search pattern pauseon each search detection, and enter a single-targettrack mode for a brief period.
  20. 20. PULSE DOPPLER RADARWilliam H. LongDavid H. MooneyWilliam A. SkillmanWestinghouse Electric CorporationReference

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