地波综合脉冲孔径雷达的数字频率源设计

Design of digital frequency synthesizer for ground-wave synthetic pulse and aperture radar

针对地波综合脉冲孔径雷达的性能要求,提出采用多个DDS芯片AD9854设计多载频数字频率源,同时产生多个不同载频的线性调频中断连续波(LFMICW)信号,并且每路发射信号的频率和初相可控;研究利用DDS产生LFMICW信号的有效方法;利用FPGA设计多片DDS的控制逻辑并实现与计算机的串行通信协议。测试结果表明,该数字频率源的相位噪声在偏离载波1 Hz处达-92.6 dBc/Hz,满足高频地波雷达进行长时间相干积累对频率源稳定性的要求。

An approach to design a digital frequency synthesizer of multiple carrier frequencies for the ground wave synthetic pulse and aperture radar, with multiple DDS chips AD9854 is presented. The synthesizer generates multiple signals of linear frequency modulated interrupted continuous wave （LFMICW） for simultaneously transnuission. The signals should have different carrier frequencies and controllable initial phases. An effective method of generating LFMICW by DDS is analyzed. The design of the FPGA control logic and the realization of the computer serial communication protocol are presented as well. The experimental results indicate that the phase noise of the frequency synthesizer is -92.6 dB cat 1 Hz, which meets the stability demands of high frequency ground wave radar for long-term coherent integration.