Focusing High-Maneuverability Bistatic Forward-Looking SAR Using Extended Azimuth Nonlinear Chirp Scaling Algorithm

In high-maneuverability bistatic forward-looking synthetic aperture radar (HMBF-SAR) imaging, the acceleration leads to an increased residual range curve and a deepened 2-D spatial variance of Doppler parameters, which cannot be processed by the traditional algorithms. To address these problems, this article establishes a more accurate digital representation for the HMBF-SAR model and investigates an extended azimuth nonlinear chirp scaling (EANLCS) imaging method. In the flowchart of this article, we first propose a more precise slant range model with improved expansion coefficients and define the range and azimuth direction of HMBF-SAR imaging. Then, a novel fast reference point (i.e., azimuth and range reference point) selection method is proposed to analyze the 2-D spatial variance of signal characteristics, which is used to construct a high-order model of residual range cell migration and Doppler parameters. Based on the above analysis, we put forward an advanced imaging algorithm of combining the second-order keystone and EANLCS to compensate for the increased residual range curve and 2-D spatial variance of Doppler parameters. Finally, the effectiveness of the proposed HBMF-SAR method is verified by several numerical simulations and comparative studies based on both the simulated and raw data.