ESPTR: Pulsed Doppler Radar - Serwer pracowniczy...

Radar types Pulsed Doppler Radar Clutter �ltering

ESPTR: Pulsed Doppler Radar

Jacek Misiurewicz

April 13, 2015

Jacek Misiurewicz ESPTR: Pulsed Doppler Radar


Radar types

By transmit waveform:I Continuous wave

I Doppler only (police, toilet, security...)I FMCWI Noise radars

I Pulsed

I Passive

By usage:

ATC Air Tra�c Control

I Maritime: harbour, navigation

I Car mounted: parking, safety...

I Airborne: collision, meteo, �ghter, Joint Stars, Bryza

I Satellite (EarthObservation)

By scan: �xed, pivot, rotary, electronic (+ conformal)Search or tracking mode.



Meteo radar

I Imaging of water/ice inatmosphere

I Velocity, turbulence, windpro�lers (VHF)

Techniques: Doppler, polarimetry,3D imaging...Frequency bands:

I L = 1-2 GHz: clear air turbulence study,

I S = 2-4 GHz: far range observation

I C = 5.470-5.725 GHz: medium range (TDWR),

I X = 9-10.5 GHz: small particles (cloud development)



Velocity measurement

−→Doppler shift measurement

xR(t) = AT (t−R0/c−vt/c)e jφM(R0/c+vt/c) e j(ωt)e−jω(R0/c)e−jωvt/c

Example: 10GHz, 70 m/s ....

I Min velocity: ground/sea/meteo clutter (ATC), time-on-target(METEO)

I Max velocity (frequency): (inverse of) modulation period



Bistatic radar network

dBZ: dB w.r.t. 1mm6m−3 (number of drops per unit volume andthe sixth power of drop diameter).



Airborne Pulse-Doppler radarSearch radar: AWACS and Bryza-1RM

(wikimedia

commons)Jacek Misiurewicz ESPTR: Pulsed Doppler Radar


Airborne Pulse-Doppler radarFighter - multifunction radar

Mechanically scanned Electronically scannedMiG-29 radar (wikimedia commons)



ATC radar

Transmitter: Pulsed chirp (or other modulation).Common: Antenna, scan mechanism, waveguides, rotary joint, T/RswitchReceiver:

I Protection, LNA, mixer, IF, pulse compression, quadraturedemodulation (sin/cos problem −→@blackboard), range gate−→range-azimuth plane

I Clutter �lter, CFAR, detection, integration, 2nd threshold(−→raw video)

I Object extraction (clustering raw video �white� areas into−→plots)

I Track initiation, plot to track association, tracking (−→tracks)



A targetRaw video (unthresholded) - two scans overlaid



ATC radar display

−→PPI display (other displays are history now)

(from radartutorial.eu)



Clutter

Ground/meteo clutter Sea clutter

from radartutorial.eu



MTI/MTD

I Clutter is low-pass (in a stationary radar): use a HF �lter

I Blind speed problem −→vary the PRF

MTI pulse-to-pulse stagger

MTD block stagger

Filter characteristics with stagger: poor!−→variable coe�cient �ltersMTD: FFT �lter bank (or equivalent)Weather clutter: non-zero Doppler, complex �lter coe�cients,adaptive �lters (MTI)Velocity measurement (CRT with MTI or MTD).



Blind speed

from radartutorial.eu



MTI/MTD sampling

MTI

Incoherent processing −→ integration gain by averaging noise

MTD

Coherent processing −→ integration gain by accumulating energy& averaging noise!



CFAR

Constant False Alarm Rate



Pulse compressionTechnically � just a matched �lter....

PC with a frequency-dependent delay system (From radartutorial.eu)

Compression ratio: BT product.

I Chirp (−→compression line, electromechanical �lter)

I Bi- and polyphase

I Pseudorandom

Range sidelobes.Warning: some people use the term �compression� for �deramping�

−→ see the lecture on FMCW radar



ECM/EPM

Electronic CounterMeasuresElectronic Protection Measures (a.k.a. ECCM - ElectronicCounter-CounterMeasures).Cha�.Jamming: detection + diversity, agility.Adaptive jamming/false echoes −→pulse coding, pulse stagger


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