A Time–Frequency Hybrid Domain Imaging Algorithm for High-Dive-Angle Hypersonic Vehicle-Borne SAR

Due to the large diving trajectory, the design of the imaging algorithm remains an exceptionally difficult task for hypersonic synthetic aperture radar (SAR). In this article, an accurate range model that accounts for the impact of higher-order motion factors on imaging performance is established. Based on the model, the signal characteristics are analyzed, which indicates that the design of the imaging approach faces greatly challenges such as severe cross-couplings and significant spatial variations (SVs). In view of these issues, a time–frequency hybrid domain imaging algorithm (TFHDIA) is proposed for hypersonic vehicle (HSV)-borne SAR systems with a large diving trajectory. The cross-couplings are significantly reduced by azimuth preprocessing. The 2-D SV in the range cell migration (RCM) and the first-order SV in the Doppler parameters (DPs) are eliminated through the fractional Fourier transform (FrFT) and the extended keystone transform (EKT). Additionally, the higher-order SVs of DPs are removed by the phase filter bank, which includes range, azimuth, and cross-coupling spatially variant phase error compensation filters. The proposed algorithm exhibits strong capabilities in eliminating SVs and effectively reducing cross-coupling, making it particularly suitable for HSV SAR systems with large diving trajectories. Simulation and actual acquired data results validate the efficacy of the proposed algorithm.