A polar format algorithm (PFA) as a high-efficient imaging method is widely used in bistatic spotlight synthetic aperture radar (SAR). In cases where motion error causes great defocusing in PFA images, phase gradient autofocus (PGA) is suitable for motion error compensation due to its robustness. However, a significant coupling of range-azimuth directions in bistatic SAR (BiSAR) makes conventional PGA unapplicable in PFA images. For this limitation, this letter gives the solution to the adaptability of PGA in BiSAR based on the azimuth migration correction in the wavenumber domain. The bistatic motion error is modeled, and the caused phase error is derived and analyzed. Through the wavenumber-domain analysis, the 2-D coupling is indicated still existing after polar format imaging, unlike other algorithms that utilize range cell migration correction (RCMC). Then, a phase compensation for the migration of azimuth direction is proposed to remove the 2-D coupling. Based on this, the new autofocus arithmetic flow for bistatic PFA is designed. The effectiveness of the proposed method is verified by numerical simulations.

中文翻译：

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用于双基地SAR极性格式成像的方位角校正的相位梯度自动聚焦

极坐标格式算法（PFA）作为高效成像方法已广泛应用于双基地聚光合成孔径雷达（SAR）。在运动误差导致PFA图像严重散焦的情况下，由于其稳健性，相位梯度自动聚焦（PGA）适用于运动误差补偿。但是，双基地SAR（BiSAR）中距离-方位角方向的显着耦合使得常规PGA在PFA图像中不适用。针对这一限制，本文基于波数域中的方位偏移校正，给出了PGA在BiSAR中的适应性解决方案。对双基地运动误差进行建模，并推导和分析引起的相位误差。通过波数域分析，表明极坐标格式成像后二维耦合仍然存在，与其他利用距离像元迁移校正（RCMC）的算法不同。然后，提出了一种用于方位角方向偏移的相位补偿方法，以消除二维耦合。在此基础上，设计了用于双基地PFA的新自动对焦算法流程。数值仿真验证了该方法的有效性。