多普勒频率偏置LFM信号的模糊函数分析

线性调频（linear frequency modulation , LFM）信号是研究最早、应用也最广泛的一种脉冲压缩信号，当LFM回波信号有较大的多普勒频移时，匹配滤波器仍能起到良好的脉冲压缩作用，这使得多普勒频率偏置技术得以应用。由于需要对发射信号进行多次周期扫频来获得目标的速度信息，本文根据模糊函数定义推导了多周期多普勒频率偏置线性调频（Doppler frequency shifted linear frequency modulation, DFS-LFM）信号的模糊函数以及不同DFS-LFM信号的互模糊函数，并对DFS-LFM信号参数与雷达距离和多普勒分辨性能进行了分析。分析结果表明，多周期LFM信号进行多普勒频率偏置后，分辨性能不受影响；对于多个不同多普勒频率偏置的LFM信号，距离和速度分辨能力不受影响但其最大不模糊多普勒谱宽发生改变且与频率偏置间隔有关。当多普勒频率偏置间隔大于目标最大多普勒频移时，既不会影响目标的多普勒速度分辨性能，又能充分利用多普勒频谱，降低了系统对工作频率及带宽的要求。

Analysis on Ambiguity Function of DFS-LFM signals

Linear frequency modulation (LFM) signal is one of the earliest researched and most widely used pulse compression signals. The matched filter procedure still works well in pulse compression even when the echo of LFM signal has a large Doppler frequency shift, which ensures the Doppler frequency shift technology to be applied. In this paper, ambiguity function of Doppler frequency shifted linear frequency modulation (DFS-LFM) signal and its cross ambiguity function of different DFS-LFM signals are deduced based on its definition and then range resolution and Doppler resolution of coherent pulse train are analysed. Results show that resolutions of DFS-LFM keep the same as LFM signal and that for multiple DFS-LFM signals with different Doppler shifted frequencies resolution in range and Doppler frequency do not change but the maximum unambiguous Doppler frequency is confined by the interval of Doppler shifted frequencies. When the Doppler frequency shift is greater than the maximum Doppler frequency of radar target, both range resolution and Doppler resolution still performance well. Meanwhile the Doppler spectrum is efficiently used, which reduces the requirements on the system working frequency and bandwidth.