Low-orbit Bistatic Frequency Modulated Continuous Wave SAR Imaging Method Based on Singular Value Decomposition
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摘要: 该文基于调频连续波(FMCW)信号对低轨星载双基合成孔径雷达(SAR)的成像方法进行研究。星载双基模型具有收发异置、结构灵活的特点，其非线性运动轨迹和双斜距不利于信号频谱的推导和分析。通过引入一个4阶多项式斜距模型对回波信号进行建模，接着用级数反演法得到信号两维频谱的表达式。详细分析高阶多项式系数的空变影响。对距离徙动项进行频域处理，对方位相位采用奇异值分解(SVD)的方法，将方位空变项与多普勒分离开，并引入非线性方位变标函数，通过两次连续的插值和重采样完成方位聚焦。仿真结果证明了该算法的有效性。Abstract: The imaging method of low-orbit bistatic SAR based on Frequency Modulated Continuous Wave (FMCW) signal is studied in this paper. The spaceborne bistatic model has the feature of transceiver separation and flexible structure. The nonlinear motion trajectory and bistatic slant range history are not conducive to the derivation and analysis of signal spectrum. The signal is constructed by a fourth-order polynomial slant range model. The expression of the two-dimensional spectrum of the signal is obtained by the method of series reversion. The spatial variation effect of the high-order polynomial coefficients is analyzed in detail. The range migration term is compensated in frequency domain. The azimuth phase is processed by the Singular Value Decomposition (SVD) method. Then the azimuth spectrum is divided into Doppler focusing terms and azimuth variation terms. A nonlinear azimuth scaling function is introduced. The azimuth variation can be completely corrected by two consecutive interpolations and resampling. The validity of the proposed method is verified by the simulation experiments.
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表 1 星载轨道及雷达仿真参数
参数名称 参数值 参数名称 参数值 轨道高度 500 km 载频 35.75 GHz 离心率 0.05 信号带宽 150 MHz 下视角 31.5° 脉冲重复频率 4000 Hz 占空比 85 % 采样率 25 MHz 双星间距 10～12 km 合成孔径时间 0.5 s 场景宽度 5 km×5 km 地距分辨率 1.7 m×2.5 m 
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表 2 点目标聚焦性能评估(dB)
目标点 PSLR ISLR 距离 方位 距离 方位 PT1 –13.0384 –13.3730 –9.5939 –10.2401 PT4 –13.1874 –13.3809 –9.5523 –10.4050 PT5 –13.1452 –12.8488 –9.5117 –9.9738 PT6 –13.1879 –13.3270 –9.5602 –10.4058
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