A High-Order Phase Correction Approach for Focusing HS-SAR Small-Aperture Data of High-Speed Moving Platforms

The squinted imaging mode has been successfully applied to synthetic aperture radar (SAR) mounted on moving platforms of high speed. The developed focusing algorithms for squint SAR data usually perform the linear range walk correction (LRWC) in the azimuth time domain as the first step, to mitigate the bulk range-azimuth coupling. Unfortunately, when applied on high-speed platforms with large squint angle and large azimuth scene length, these algorithms for airborne SAR considering only the first-order azimuth dependence of the Doppler frequency-modulation (FM) rate will introduce a large residual phase error, and therefore degrade the final radar image quality. Meanwhile, those algorithms, originally designed for full-aperture data, cannot be applied directly to the small-aperture data. Due to these problems, a high-order phase correction approach (HPCA) combined with SPECAN operation for focusing high-squint SAR (HS-SAR) small-aperture data is developed in this paper to deal with the above issues. In this approach, both the first- and the second-order azimuth dependence of the Doppler FM rate are compensated for, and the same to the cubic phase term, by introducing a correction phase term in the azimuth frequency domain. The presented approach has been successfully used to focus the real airborne radar data recently.