Space/time/frequency methods in adaptive radar - New Jersey ...

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ABSTRACTSPACE/TIME/FREQUENCY METHODS IN ADAPTIVE RADARbyChristopher D. PeckhamRadar systems may be processed with various space, time and frequency techniques.Advanced radar systems are required to detect targets in the presence of jammingand clutter. This work studies the application of two types of radar systems.It is well known that targets moving along-track within a Synthetic ApertureRadar field of view are imaged as defocused objects. The SAR stripmap mode istuned to stationary ground targets and the mismatch between the SAR processingparameters and the target motion parameters causes the energy to spill over toadjacent image pixels, thus hindering target feature extraction and reducing theprobability of detection. The problem can be remedied by generating the imageusing a filter matched to the actual target motion parameters, effectively focusingthe SAR image on the target. For a fixed rate of motion the target velocity canbe estimated from the slope of the Doppler frequency characteristic. The problemis similar to the classical problem of estimating the instantaneous frequency of alinear FM signal (chirp). The Wigner-Ville distribution, the Gabor expansion, theShort-Time Fourier transform and the Continuous Wavelet Transform are comparedwith respect to their performance in noisy SAR data to estimate the instantaneousDoppler frequency of range compressed SAR data. It is shown that these methodsexhibit sharp signal-to-noise threshold effects.The space-time radar problem is well suited to the application of techniquesthat take advantage of the low-rank property of the space-time covariance matrix.It is shown that reduced-rank methods outperform full-rank space-time adaptive
Page 1: Copyright Warning & RestrictionsThe
Page 5 and 6: SPACE/TIME/FREQUENCY METHODS IN ADA
Page 7: APPROVAL PAGESpace/Time/Frequency M
Page 10 and 11: ACKNOWLEDGMENTI would like to begin
Page 12 and 13: ChapterPage3.2.1 Non-Adaptive Beamf
Page 14 and 15: FigurePage2.22 Scalogram of a linea
Page 16 and 17: CHAPTER 1INTRODUCTIONVarious space,
Page 18 and 19: 3the target. In this work we study
Page 20 and 21: 5support consists of a population o
Page 22 and 23: 7processing. This is explained by t
Page 24 and 25: 92.1 An Overview of Synthetic Apert
Page 26 and 27: 11Figure 2.2 SAR cross-range Dopple
Page 28 and 29: 13Through the expression for the on
Page 30 and 31: 15Illumination pattern onEarth's su
Page 32 and 33: 17Figure 2.6 Time-frequency descrip
Page 34 and 35: 19Figure 2.7 Computation of the sho
Page 36 and 37: 21Figure 2.9 Spectrogram of a multi
Page 38 and 39: 23where 9/ is the Hilbert transform
Page 40 and 41: Figure 2.11 Gabor Transform of a si
Page 42 and 43: 272.3.3 Continuous Wavelet Transfor
Page 44 and 45: 29Figure 2.13 Time-Frequency resolu
Page 46 and 47: Figure 2.14 Scalogram of a sine wav
Page 48 and 49: Figure 2.16 Regions of influence co
Page 50 and 51: Figure 2.17 WVD transform of a sine
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37Figure 2.18 Example of WVD cross
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39(a) Contour plot of the WVD of a
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41(a) Contour plot of the STFT of a
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43(a) Contour plot of the Gabor exp
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452.5 Time-Frequency Analysis in No
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47Consequently, when the slope S, i
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49where:Doppler phase shift due to
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51(a) Contour plotFigure 2.24 SAR i
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53(a) Contour plotFigure 2.26 SAR i
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55calculated in each case. In this
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57(a) Moving target with synthetic
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Figure 2.31 SAR with 2 moving targe
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61Figure 3.1 Space-time adaptive ar
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63Figure 3.3 Airborne radar basic g
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subspace is formed using the remain
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67where k is a gain constant and R
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69The scalar beamformed noise estim
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71are the desired signal, interfere
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CHAPTER 4REDUCED-RANK PROCESSINGThe
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75Figure 4.2 Reduced-rank GSCThis m
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77This relation establishes an equi
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79The conditioned SNR is a random v
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81The performance of the GSC proces
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83For large interference eigenvalue
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85the steering vector s, and the ve
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87(a) CSNR vs Rank order for other
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89Figure 5.4 CSNR vs Rank order for
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91Figure 5.6 Theoretical and simula
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93Figure 5.8 CSNR vs CNRThe signal
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950.80.80.6 0.6~(5'0.4IC!J0.40.20.2
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97the spatial domain. The target is
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99(a) Training outside the target r
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101(a) Training around the target r
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103Figure 5.15 Angle scan with the
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CHAPTER 6CONCLUSIONSThis work has b
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107also presented. The Sample Matri
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APPENDIX ADISCRETE COSINE TRANSFORM
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111This matrix is formed using the
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REFERENCES1. Leon Cohen. Time-frequ
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11523. Franz Hlawatsch and G. Faye
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11750. Daniel F. Marshall. A two st
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INDEXanalytic signal, 21array imper
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