INVESTIGATION OF FREQUENCY AGILITY FOR LPI-SAR WAVEFORMS
Wagner, Zachary A.
Pace, Phillip E.
Garren, David A.
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This thesis investigates the feasibility of using Costas frequency shift transmission waveforms to generate spotlight Synthetic Aperture Radar (SAR) images. A spotlight SAR image formation algorithm is used to evaluate the radar returns from scenes containing multiple point scatterers. Two-dimensional imagery is used to investigate the sidelobe effects. The peak sidelobe ratio (in dB) is determined from the one-dimensional slices in both the down-range and cross-range dimensions. Three unique Costas frequency shift sequence lengths are used in the investigation, N = 15, 100, and 150. Results of this investigation show that Costas frequency shift sequences are practical for the formation of spotlight SAR images. The autocorrelation sidelobe levels resulting from the Costas waveform are reduced with an increasing sequence length, providing an improved peak-to-sidelobe ratio. Image scenes with multiple neighboring scatterers are interrogated. Results show a spotlight SAR image peak-to-sidelobe ratio of – 20 dB, – 40 dB, and – 44 dB for N = 15, 100, and 150, respectively, thus offering the potential for producing high-quality spotlight SAR imagery while maintaining the strategic advantages of low probability of intercept.
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