当目标保持匀速运动时，回波信号经过FFT后的输出信噪比正比于信号的有效积累时间长度，采用FFT比相测距算法，经过FFT计算得到的相差与目标中间时刻的距离相对应。但当目标机动时，回波信号的多普勒频率为时变量，基于FFT处理的相参积累输出信噪比下降。该文首先对机动目标情况下基于FFT比相测距方法进行了理论分析，得到了距离与相差的关系式，给出了不同加速度下FFT输出信噪比损失曲线。最后仿真结果验证了理论分析的正确性。

When a target is of constant velocity, then the output Signal-Noise-Ratio (SNR) of FFT is proportional to effective integration time. The phase difference obtained by ranging algorithm based on FFT phase comparison a corresponds to target range at the centeral time. But Doppler frequency of echo is time-varying when target is maneuvering. So output SNR of FFT coherent integration decreases. This paper first theoretically analyzes ranging method based on FFT phase comparison for maneuvering target. Relationship between range and phase difference is derived. Loss curve of FFT output SNR is presented for different accelerations. Finally simulation results show the validity of theory.

TN958