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SAR在大斜视时距离向和方位向存在着严重的耦合,为了消除这种耦合,分析了一种基于非线性调频变标NCS的改进RD算法。它充分利用大斜视角回波信号的大距离走动、小距离弯曲的特点,首先在距离向校正距离走动,然后采用非线性调频变标NCS来补偿方位向调频率的空变性,最后通过几何校正完成目标成像。同时仿真模拟场景的原始回波信号并对改进后的算法进行仿真,仿真结果表明,该算法可有效补偿方位向调频率的空变性,具有较高的精度,满足大斜视角下的成像要求。“,”To eliminate the serious coupling between azimuth and range for SAR in large squint mode,an improved RD imaging algorithm based on nonlinear chirp scaling was proposed,which made full use of the characteristic of SAR echo signal in large squint mode,which featured large range walk and small range curvature.First,range walk was corrected.Second,nonlinear chirp scaling operation was adopted to compensate the azimuth-dependent chirp rate.Finally,geometry correction was used to correct geometric distortion.Meanwhile the raw echo signal of the scene and the improved algorithm was simulated.Simulation results illustrate that it efficiently compensates the azimuth-dependent chirp rate,possesses high precision and satisfies the imaging quality of SAR in large squint mode.