ch8 radar signal processing
DESCRIPTION
radar signal processingTRANSCRIPT
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Ch 8
Radar Signal Processing
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@Prof Y Kwag 2
Lecture 8 : Radar Signal Processing
Objective - - MTI, MTD - SAR
- Introduction - Signal Integration - Correlation / Convolution - Moving Target Indicator (MTI) - Moving Target Detection (MTD) Doppler Processing - PRF Ambiguity - Improvement Factor - High Resolution Radar - SAR - Reference
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@Prof Y Kwag 3
Introduction
RSP objective - Improve S/N and Pd of target - High clutter rejection - High Interference/jamming rejection - Exact information extraction : characteristics
Environments - Clutter - surface, volume clutters - Interference jamming, ECM, spiky noise - Target RCS scintillation SW 1~4 - Noise & noise jamming = randomness(amp/phase) - Desired target = small, orderliness phase
Differences between signal and noise - orderliness vs randomness in phase & amp - rate of changes of the phase of orderly signal
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@Prof Y Kwag 4
Introduction
Processes - signal integration : vector sum, orderly from hit-to-hit - correlation(pulse compression) : matching the desired signal to the reference
- filtering & spectrum analysis windowing used in correlation & spectral analysis to reduce leakage error
convolution : windowing in time convolution in freq. Domain
Block diagram - Digital pulse compression
< Typical signal Processor, Digital Pulse Compression >
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@Prof Y Kwag 5
Introduction
- Analog pulse compression
< Typical signal Processor, Analog Pulse Compression >
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Sampling Range &Doppler
Range Bin Rate - PRF : rate at which an individual target can change
target sampling freq.
phase shift from hit to hit caused by the Doppler shift.
sample at a rate or equal to at least twice the highest Doppler
frequency, otherwise Doppler ambiguity
- Range/Doppler trade-off
Range bin rate = A/D sampling
= Range resolution
Doppler sampling rate = PRF
16 FFT (ex)
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@Prof Y Kwag 7
PRI Dwell Time, CPI,
Burst, Scan
SCAN
DWELL TIME
CPI
RANGE
CELL
P1 P2 Pa P1 P2 Pa P1 P2 Pa
Scani-1 Scani Scani+1
DT1 DT2 DTk DTm-1 DTm
R1 R2 Ri Rk Rj Rl
CPI1 CPI2 CPI3
Effective Range Guard Time
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@Prof Y Kwag 8
Radar Range-Gated Data Structure
Bean of No. : 360
K
Pulse Interation of No. : T
TN
Cell Range of No. : T
M
BW
i
3 D Structure
Rangel/Azimuth/Doppler
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(1)
(2)
1st PRF 2nd PRF
PRF
f
f
Radar Echo Signal
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(4) AMTI
PRF
f
(3) MTI
PRF
f
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PRF f
PRF/N
f
(5) Doppler
Filter Bank
(FFT)
(6) CFAR
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Signal Integration
Non-Coherent Integration - Signal plus Noise
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Signal Integration
Non-Coherent Integration - Signal plus Clutter
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Signal Integration
Coherent Integration - Stationary Target
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Signal Integration
Coherent Integration - Bin-1 Moving Target
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Signal Integration
Integration Loss - Type of integration (coherent or non-coherent) - Number of pulse integrated - Required detection & false alarm probability - Target fluctuation statistics - Processing window used
Coherent integration loss is determined by - processing window used
Window loss for most window is less than 3 dB
- target fluctuation statistics
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@Prof Y Kwag 17
Correlation
Correlation - process of matching two waveforms in time domain - determine the time at the maximum correlation coefficient
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< Correlation >
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@Prof Y Kwag 18
Convolution
Continuous Convolution
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< Convolution >
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@Prof Y Kwag 19
Gated CW Convolution
Gated CW Convolution
< Spectrum of Gated CW Wave from Convolution >
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Clutter Rejection
MTI and Pulse Doppler Processing
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Air Defense Scenario
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Terminology
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Doppler Frequency
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Example Clutter Spectra
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MTI and Pulse Doppler Waveforms
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MTI Processing
Separate MTI Process
< Separate MTI Process for Each Range Bin >
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Two Pulse MTI Canceller
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MTI Processing
Single Delay Line Canceller
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@Prof Y Kwag 29
MTI and Doppler Processing
Double Delay Line Canceller (three pulse canceller)
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@Prof Y Kwag 30
MTI and Doppler Processing
Delay Line with Feedback (Recursive)
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@Prof Y Kwag 31
Moving Target Indicator (MTI) Processing
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Clutter Spectrum Characteristics
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MTI Improvement Factor
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MTI Improvement Factor Examples
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Pulse Doppler Processing
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Moving Target Detector (MTD)
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MTI and Doppler Processing
PRF Stagger - Blind Doppler occurs when the freq. shift is an integer multiple of sample rate (PRF)
pulse-to-pulse PRF stagger
look-to-look & scan-to-scan stagger
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@Prof Y Kwag 38
Staggered PRFs to Increase Blind Speed
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@Prof Y Kwag 39
Blind Rejection Filter
Staggering Filter Response
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blind speed
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< Three Delay Non-Recursive Filter Response >
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@Prof Y Kwag 40
Range Ambiguities
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Doppler Ambiguities
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Unambiguous Range and Doppler Velocity
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Limitation on Improvement Factor
Limitations on the Improvement Factor With good canceller or filter bank design, cancellation can be
essentially perfect if
- The antenna is stationary (not scanning)
- The clutter is totally stationary, with a zero width spectrum
- Enough rang sweeps are gathered to totally charge the canceller,
or in the case of a filter bank, the number of points processed is large
- The system is totally linear
- Pulse-to-pulse stagger is not necessary to avoid blind Doppler shifts
Many MTI systems are specified and tested with the antenna stationary.
Scanning is, of all the factors listed, the most important in limiting the
improvement of MTI and MTD. Without scanning or with step-scanning,
the same antenna gain is pointed at the clutter throughout the dwell
and the echo from non-moving clutter is constant.