Extended Azimuth Nonlinear Chirp Scaling Algorithm for Bistatic SAR Processing in High-Resolution Highly Squinted Mode

Accurate focusing of highly squinted azimuth-variant bistatic synthetic aperture radar data is a difficult issue due to the relatively large range migration, sensibility of the higher order terms, and the inherent geometric variance. To accommodate for this problem, extended azimuth nonlinear chirp scaling algorithm is investigated in this letter. First, range-azimuth coupling is mitigated through a linear range walk correction operation, and then, bulk secondary range compression is implemented to compensate the residual range cell migration and cross-coupling terms. Following which, the characteristics of the azimuth-dependent quadratic and cubic phase terms are analyzed, and modified scaling coefficients are derived by adopting higher order approximation and incorporating the azimuth-dependent range offset caused by the inherent geometric configuration. Compared with traditional nonlinear chirp scaling method, large azimuth depth of focusing can be realized without changing the overall procedure. Simulation results validate the effectiveness of the proposed algorithm.