在线性调频雷达系统中，若发射机输出的脉冲信号起始相位是不相参的，则接收机不能根据回波信号解调出准确的多普勒参数。引入了前导帧序列，以控制直接数字合成(DDS)输出信号的相位初始化，从而实现最终输出脉冲信号起始相位与参考时钟相参。该方法简单实用，仅需更改FPGA程序，无需对硬件电路做任何改动。实验结果验证了该方法的有效性。

In linear frequency modulation system, the receiver cannot demodulate the Doppler parameter correctly based on the return signal if the initial phase of the transmitter output is not coherent. A prior frame sequence is introduced to realize the coherence between the initial phase of the output pulse signal and the reference clock by initializing the Direct Digital Synthesis(DDS)’s phase accumulator. The proposed method is simple and practical, because it just only needs to modify the FPGA program without any changes to the hardware circuit. The effectiveness of the method has been verified by the experimental results.