Improved reliable high-order SPECAN algorithm for highly squinted SAR imaging processing

For the processing of highly squinted synthetic aperture radar (SAR) echo signals, three key challenges need to be considered: rectifying the nonzero Doppler centroid, compensating for azimuthal side-lobe defocusing (ASLD), and correcting the range cell migration (RCM). To address these three problems, we developed a reliable improved fourth-order spectral analysis (SPECAN) algorithm for highly squinted SAR imaging in this study. First, we present a fourth-order phase model (FoPM) that is more suitable for the highly squinted SAR system through a theoretical analysis. Second, based on the FoPM, we derive an improved fourth-order SPECAN algorithm in detail. In this derivation, the nonzero Doppler centroid, the ASLD, and the RCM caused by the high squint angle are corrected. Moreover, the whole simulation procedure of the improved algorithm only contains fast Fourier transform and complex multiplication, so the proposed algorithm can efficiently process highly squinted SAR echoes. Furthermore, the results of a comparison with the traditional SPECAN algorithm show the better performance of the proposed algorithm.