低杂散宽带直接数字频率合成技术研究

Modern radar and communication systems have raised extremely demanding requirements for the synthesized frequency hopping time, bandwidth and noise levels. Be treated as the main development direction, direct digital frequency synthesis (DDS) has an absolute advantage in terms of frequency switching time. However, its spurious performance in the wideband spectral range is far below the system requirements, which has seriously hampered the development and application of DDS technology. Base on this fundamental phenomena, this research proposes to involve high order sigma-delta modualtiong for the conventional DDS phase accumulator, to set up a comprehensive DDS phase noise and spur level model. The selection method of various structure and order of sigma-delta modalators, the combination of multiple and differential modulation structure of sub-band output algorithms, weights optimization algorithm are proposed simultaneously. Digital pre-distortion compensation approach is utilized to further suppress the spurious component at a series of dedicated frequencies. The proposed off-line processed phase accumulation method is able to achieve high-speed DDS, carrying algorithm research, and increasing the output frequency. Combined with a variety of noise reduction algorithms and implementation of innovative integrated broadband, agile, low-noise direct digital frequency synthesizer.

现代雷达与通信系统对频率合成的跳频时间、带宽、噪声水平都提出了极为苛刻的要求，直接数字频率合成（DDS）作为未来相干频率合成的主要发展方向，在跳频时间方面占有绝对优势，但宽带频谱范围内的杂散性能远低于系统需求，严重制约了DDS技术的发展和应用。本课题针对DDS宽带范围的高杂散这一基础性问题开展研究，在相位累加信号处理过程中引入高阶和差调制结构，建立基于和差调制的DDS相位噪声与杂散模型，提出和差调制多种结构和阶数选择、权值优化算法、多种和差调制结构分频段组合输出算法、数字预失真补偿杂散抑制算法，在降低输出频谱相位噪声水平的同时减少杂散数量并降低杂散幅度。提出基于相位信息预处理的高速DDS实现方法，承载算法研究的同时提高输出频率。结合多种降噪算法和创新性实现方法可综合实现宽带、捷变、低噪声的直接数字频率合成。

直接数字频率合成（DDS）是新一代频率合成技术，但宽带频谱范围内的杂散性能是制约DDS技术的发展和广泛应用的瓶颈。本课题分析了DDS的杂散产生的根源，提出了改善DDS杂散性能的方法，研究了基于FPGA的低噪声高速DDS实现技术，并进行了实际应用验证。针对DDS宽带范围内的高杂散这一基础性问题开展研究，在相位累加信号处理过程中引入高阶和差调制结构，建立了基于和差调制的DDS相位噪声与杂散模型，在降低输出频谱相位噪声水平的同时减少杂散数量并降低杂散幅度。.通过使用本课题研究实现的高速DDS硬件，为S频段小目标探测雷达实现了快速低噪声跳频本振和相位编码激励信号，使原本被高杂散占据的区域的噪声得到了有效抑制，综合降低了杂散电平，拓展了该雷达在距离-多普勒二维区间的可探测小目标范围。