中文说明：
线性调频信号是一种雷达常用的电磁波信号，当雷达信号检测到目标时候，反射后得到雷达回波信号，此时由于多普勒效应，信号的频率发生偏移，这个源码仿真出雷达检测到目标距离信息的回波信号。
English Description：
LFM signal is a common electromagnetic wave signal used by radar. When the radar signal detects the target, the radar echo signal is obtained after reflection. At this time, the frequency of the signal is offset due to Doppler effect. This source code simulates the echo signal of the target distance information detected by radar