GPS在双（多）基地高频地波雷达中的应用

针对双(多)基地高频地波雷达高精度同步问题，给出了一种利用GPS模块进行校频的时间同步方法。该方法采用FPGA器件，外同步源来自GPS接收信号，通过对FPGA内部设计的数字鉴相器输出的相差进行处理，并通过时间步长由小增大的方式调整恒温晶振的调谐电压，结果获得很高的频率同步精度。输出各信号的时间关系由软件设定，以计数方式产生，不但电路简单，调试修改方便，更重要的是使各信号问的时序关系准确、稳定、可靠，减少了雷达的相位误差。考虑到GPS接收机不能正常接收到信号的情况，FPGA内部的波形产生逻辑模块还进行了冗余设计，在GPS接收机不能正确接收到信号时，产生精度由时钟保证的同步信号，确保时间同步信号的连续性。文中还给出了利用ModelSim进行仿真的结果。理论分析和仿真结果说明了该文设计方案的可行性。

Application of GPS in Bistatic(Multistatic) HF Ground Wave Radar

A technique for calibration of frequency and time synchronization is to use GPS module to solve the problem of high-precision synchronization in bistatic (multistatic) HF ground wave radar system. To that end FPGA chip is used, and the signal received from GPS is the external synchronization source in this design. The phase detector designed in FPGA reads the phase error data of the digital phase discriminator and adjusts the input voltage of OCXO by changing it in a small step gradually to a big step. As a result, a very high synchronization precision is achieved. Thus the time relationship among all signals was set up by software and generated in the mode of counting. This method not only simplifies the circuit, but also makes the time-sequence of signals precise, stable, and reliable. Moreover, it decreases the possibility of phase error generated by the system. Redundancy design of Logic module is used to produce synchronous signals whose precision is determined by clock signal thus guarantees the continuity of synchronous signals in case of GPS failure. The results of ModelSim simulation are presented. The theoretical and simulation results indicate that the design can achieve all the performances expected.