Adaptive Subaperture Approach for Spotlight SAR Azimuth Processing

This paper presents an improved step transform subaperture approach for spotlight Synthetic Aperture Radar (SAR). The step transform algorithm will obtain desired high azimuth resolution only if the linear FM rate and the sampling rate of the SAR signal satisfy a certain constraint. In order to obtain a high quality image, the minimum entropy autofocus using an adaptive order polynomial model is extended and applied before the coherent summation step in this paper. The extended autofocus processing not only compensates quadratic and higher order phase errors but also shifts the coarse-resolution response functions to their correct positions. The simulation results of 1-dimension and 2-dimension are given, and the validity of this algorithm is demonstrated.