Focus Improvement of Airborne High-Squint Bistatic SAR Data Using Modified Azimuth NLCS Algorithm Based on Lagrange Inversion Theorem

In this paper, a modified azimuth nonlinear chirp scaling (NLCS) algorithm is derived for high-squint bistatic synthetic aperture radar (BiSAR) imaging to solve its inherent difficult issues, including the large range cell migration (RCM), azimuth-dependent Doppler parameters, and sensibility of higher order terms. First, using Lagrange inversion theorem, an accurate spectrum suitable processing airborne BiSAR data introduced. Different from that based on method series reversion (MSR), it allowed derive stationary phase point while retaining double square root (DSR) slant history. Based spectrum, linear RCM correction used remove most components mitigate range-azimuth coupling, and, then, bulk secondary compression implemented compensate residual cross-coupling Following this, NLCS operation applied eliminate azimuth-dependence parameters equalize frequency modulation compression. The experimental results, with better focusing performance, prove high accuracy effectiveness proposed algorithm.