An Improved Ultrahigh-Resolution Stepped-Frequency Spaceborne SAR Imaging Algorithm

Abstract

Frequency stepping is a widely used technique for ultra-high-resolution synthetic aperture radar (SAR). Although reducing the burden of hardware, the technique increases the complexity of imaging algorithms due to the inter-subband time offsets and inter-subband errors of delay, amplitude and phase. To address the above problems, an improved ultra-highresolution stepped-frequency spaceborne SAR imaging algorithm is proposed in this paper. By generating subband images individually, performing inter-subband error estimation based on primary points, and then synthesizing the subband images in the imaging domain, the proposed algorithm effectively avoids the problem of time offsets and significantly improves inter-subband error compensation accuracy benefiting from the high SNR in the imaging domain. Besides, considering the characteristics of non-ideal factors in frequency-stepped SAR, a series of error compensation methods aiming at stop-and-go approximation, ionospheric error and tropospheric delay are integrated to the proposed algorithm. The effectiveness of the proposed algorithms is verified via computer simulations, and real data experiments are also conducted based on both an X-band spaceborne SAR system, Taijing 4-01, and a Ka-band spaceborne SAR system, Luojia 2-01.