Parameter Design and Performance Analysis for Geosynchronous SAR Sparse Spotlight Mode

Compared with low earth orbit (LEO) synthetic aperture radar (SAR), geosynchronous earth orbit (GEO) system has higher orbital altitude and longer synthetic aperture time, which shows better performance in high-resolution and wideswath imaging. Spotlight is a traditional SAR imaging mode, which improves the azimuth resolution by controlling the antenna beam to illuminate the same area. Therefore, the combination of GEO SAR and spotlight mode is beneficial to realize highresolution and wide-swath imaging. The conventional matched filtering (MF) based GEO SAR imaging algorithm can be used to obtain the focused images of the surveillance area, but the recovered results will suffer from the sidelobes, noise, and clutter. Sparse SAR imaging solves this problem well, and also shows potential in enhancing the system performance, e.g., lower pulse repetition frequency (PRF) and wider swath. In this letter, we propose a novel parameter design scheme of sparse spotlight mode for GEO SAR. It not only retains the advantages of GEO SAR spotlight mode, but also further increases the swath width without changing the hardware complexity of radar system. In addition, compared with typical spotlight mode of GEO SAR, the designed sparse one can suppress the deterioration of azimuth ambiguity signal ratio (AASR) with steering angle. Experimental results based on simulated datasets verify the designed sparse spotlight GEO SAR imaging mode.