在斜视成像模式下,合成孔径雷达回波信号的距离向和方位向之间存在严重的相位耦合效应,影响高分辨聚焦。非线性调频变标(NCS)算法在二维频域进行三次相位滤波,并补偿二次距离压缩(SRC)随距离的线性变化,在一定程度上改善了斜视成像的聚焦性能。但随着斜视角的进一步增大,三次以上的高阶相位以及SRC 随距离的非线性变化对高分辨聚焦的影响也逐渐加大,从而降低成像性能。文中提出基于回波四次相位多项式模型的改进NCS算法,该算法通过两维频域中的三次及四次相位滤波以补偿参考距离处的相位耦合项,并且考虑了SRC随距离的非线性变化对聚焦的影响。通过仿真及实测数据的成像效果验证了该方法的可行性及有效性。

On the condition of the squint mode imaging, there exits the serious phase coupling effect between the range and azimuth dimension in the echoes of synthetic aperture radar (SAR), which will have bad impact on high-resolution focusing. Nonlinear chirp scaling (NCS) algorithm performs a three-order phase filtering in the two-dimensional frequency and compensates the linear range variance on secondary range compression (SRC), which ameliorates the focusing performance to a certain extent. But with the increase of the squint angle, the influence that four-order and above phase and nonlinear range variance on SRC exert on high-resolution focusing is also augmented, which will deteriorate the imaging effect. A refined NCS based on the four-order phase polynomial model is proposed in this paper. The algorithm performs the three and four-order phase filtering in the two-dimensional frequency to compensate the phase coupling at the reference range and meanwhile compensates nonlinear range variance on SRC. The imaging results of simulation and live data demonstrate the feasibility and validity of the method are proposed in this paper.