Research On Bistatic Synthetic Aperture Radar Imaging Methods

The parallel-track bistatic Chirp Scaling algorithm is the main line of this paper. On the one hand, refined methods of bistatic Chirp Scaling algorithm are studied. On the other hand, Frequency Scaling algorithm, corresponding to Chirp Scaling algorithm, is extended to focus the general bistatic synthetic aperture radar(SAR) data.The background and significance of the research on the bistatic SAR are clarified concisely. The present bistatic SAR imaging algorithms are classified and explained carefully. The basic problems of studying bistatic SAR imaging algorithms and the special meaning of research on the parallel-track bistatic SAR imaging algorithms are also indicated.The three basic functions in the range-Doppler expression are the foundation of the Chirp Scaling algorithm. Based on the decoupling characteristic between azimuth and range dimension, the close-form azimuth modulation derived from the 2-D point-target spectrum. A close-form range curvature factor is constructed through the correspondence of the instant Doppler frequency to the squint angles. The removal of range walk in the time domain reduces the varying ranges of range curvature factor and effective range-FM rate, and enhances the varying characteristic of the algorithm.The introduction of the fractional Fourier transform into the range processing of the parallel-track of the bistatic Chirp Scaling algorithm improves the range resolution of the algorithm. The fractional matched filter, based on the fractional Fourier transform, is proved to reduce the mismatch in range compression under some conditions. The Chirp Scaling factor and the rotating angle of the fractional Chirp Scaling algorithm are calculated jointly. The reservation of the RVP from the range fractional Fourier transform betters the azimuth resolution.The corresponding relationship between the 2-D point-target spectrum and the system transfer function is testified. The sources of errors in the SAR imaging algorithms are analyzed. The two difficulties in derivation of the parallel-track bistatic SAR imaging algorithms and two conditions of the effective imaging are presented. Based on them, the performance of range compression is enhanced by introducing the basic scaling method into the parallel-track bistatic Chirp Scaling algorithm.The method of two-dimensional track rotation through compensating the instant slant range in the time domain is extended into the three-dimensional case. And that result is used with the method of velocity transformation. The combination of the two methods transforms the general bistatic SAR data into the parallel-track bistatic SAR data, from which the bistatic SAR data of general-track configuration are transformed into the ones of the parallel-track configuration. Then the parallel-track bistatic imaging algorithm can produce the image. By the construction of the suitable reference function and frequency-domain compensation function, an extended parallel-track bistatic Frequency Scaling algorithm is obtained. The close-form migration factor and SRC function enhance the focusing ability and the efficiency of the parallel-track bistatic Frequency Scaling algorithm.