船载S波段测波雷达多带宽数字下变频设计

Design of multi-bandwidth digital down conversion of shipboard coherent S-band wave radar

面对不同海况,船载S波段测波雷达数字接收机需要支持6种不同的基带采样速率和带宽。为了满足雷达各模块多功能一体化以及雷达系统对多速率多带宽的需求,提出了一种基于FPGA的多带宽数字下变频(DDC)方案,可根据接收机工作参数,动态加载适用于不同海况的抽取倍数和滤波器系数。通过坐标旋转数字计算法(CORDIC)实现了16级流水线数控振荡器(NCO)模块;对分布式算法(DA)进行改进,实现了全并行128阶FIR滤波器,并对DA通道进行时分复用;异步FIFO模块保证数据在跨时钟域无失真传输,并适当的对数据截位来节省硬件资源。最终结果表明基带I/Q信号频率准确,信噪比高达60 dB,满足设计目标和雷达使用需求,该结构可节省大量DSP乘法器和RAM资源,对DA结构时分复用后,可额外节省42.8%的查找表资源。数字下变频方案合理可行,可有效针对不同海况切换抽取倍数和滤波器系数,为后续基带信号处理器提供了稳定有效的数据来源,对雷达各模块多功能一体化具有重要参考意义。

Faced with different sea conditions, the shipboard coherent S-band wave radar digital receiver needs to support 6 different baseband sampling rates and bandwidths. In order to meet the multi-functional integration of radar modules and the radar system′s requirements for multi-rate and multi-bandwidth, an FPGA-based multi-bandwidth digital down-conversion(DDC)solution is proposed, which can dynamically load decimation multiples and filter coefficients according to the receiver operating parameters and suitable for different sea condition. A 16-stage pipeline numerically controlled oscillator(NCO)module is realized through the coordinate rotation digital computer(CORDIC);the distributed algorithm(DA)is improved to realize a fully parallel 128-order FIR filter, and the DA channel is time-division multiplexed;the asynchronous FIFO module guarantees that data is transmitted without distortion across clock domains, and the data is appropriately truncated to save hardware resources. The final result shows that the baseband I/Q signal frequency is accurate, and the signal-to-noise ratio is as high as 60 dB, which meets the design goals and radar requirements. This structure can save a lot of multipliers and RAM resources. After the DA structure is time-division multiplexed, it can save an additional 42.8% look-up table resource. The designed DDC is reasonable and feasible, which can effectively switch the decimation factor and filter coefficient according to different sea conditions, and provide a stable and effective data source for the subsequent baseband signal processor. This has important reference significance for the multi-functional integration of radar modules.