中文摘要：

在一站固定式双站SAR成像处理中，该文针对距离-方位2维空变描述不够准确导致成像性能迅速下降的问题，提出一种新的椭圆模型精确描述一站固定式大基线双站SAR的距离-方位空变特性，并基于此推导了改进的非线性调频变标（NLCS）成像算法。在距离向，首先利用相位去斜完成距离去走动和多普勒中心矫正，接着对剩余距离单元徙动和距离方位高次耦合项进行了去除处理。在方位向，根据一站固定式双站SAR的2维空变特性，提出了一种用于描述回波距离-方位空变特性的椭圆模型，基于该模型对空变的回波方位调频率进行了分析，并重新推导 NLCS 算法的方位变标函数和方位压缩系数。理论分析与仿真结果证明，所提出的模型不仅揭示了一站固定式大基线双站SAR数据的2维空变特性，而且对回波的距离-方位空变给出了更精确的解析式描述，使得基于该模型改进的NLCS算法可以获得更好的成像处理效果。

英文摘要：

In One-Stationary Bistatic Synthetic Aperture Radar （OS-BiSAR） imaging, imprecise description of 2-D range-azimuth space-variant property usually leads to deterioration of final SAR image rapidly. In order to solve this issue, a new ellipse model is proposed to precisely describe range-azimuth space-variant property of OS-BiSAR with large baseline, and an improved Non-Linear Chirp Scaling （NLCS） algorithm is also derived based on this model. First, a phase de-ramp operation is performed to remove the linear Range Cell Migration （RCM） and Doppler centroid in range frequency domain. Then, the residual RCM and high order range-azimuth coupling terms are removed. Thirdly, a new ellipse model is established to describe range-azimuth space-variant property of OS-BiSAR, and then the azimuth frequency modulation rate of space-variant echo is analyzed. Moreover, azimuth scaling function of NLCS and azimuth compression factors are re-derived. Theoretical analysis and simulation results show that the proposed model not only reveals the property of 2-D azimuth-variant in OS-BiSAR, but also provides a precise analytical expression to depict the 2-D range-azimuth space-variant property of OS-BiSAR. Furthermore, simulation results validate that the improved NLCS algorithm based on this new model has high imaging performance.