A Range Grating Lobes Suppression Method for Stepped-Frequency SAR Imagery

Stepped-frequency synthetic aperture radar (SAR) system errors induce the periodic magnitude error and phase error (MEPE) in the synthesized wideband spectrum. The periodic MEPE results in periodic grating lobes in the high range resolution profile, which degrade the SAR image quality seriously. This paper presents a data-driven grating lobes suppression (GLS) method, named MEPE-GLS, to suppress grating lobes by estimating and compensating the periodic MEPE. Based on the dominant targets' image domain data, MEPE-GLS estimates the phase error and magnitude error by the weighted maximum-likelihood estimation and weighted least-squares estimation, respectively. In order to improve the signal-to-clutter-and-noise ratio (SCNR) of the data employed in the MEPE estimation, MEPE-GLS applies the discrete windows to selected targets to remove clutters between two adjacent grating lobes. Compared with conventional GLS methods, MEPE-GLS removes grating lobes effectively while at the same time preserves the original image information, and has no restriction on hardware, scenes, and spectrum reconstruction methods. Simulation and real data experiments validate the effectiveness and robustness of MEPE-GLS.