捷变PRF高分辨宽覆盖星载SAR信号处理技术

Advanced spaceborne synthetic aperture radar (SAR) systems with continuous pulse repetition frequency (PRF) variation Advanced multichannel spaceborne synthetic aperture radar (SAR) systems with continuous pulse repetition frequency (PRF) variation play an important role in future spaceborne SAR high-resolution wide-swath imaging applications. Working principles and system performances of the advanced SAR systems with continuous PRF variation are systematically researched and analyzed. Combined with stripmap and sliding spotlight imaging modes, high-resolution wide-swath modes are presented. Afterwards, echo properties of such advanced imaging schemes are deeply researched. The coupling nonuniform sampling problem between continuous PRF variation and Doppler spectrum aliasing is analyzed, and the way to this problem is proposed. Meanwhile, a modified digital beamforming (DBF) on receive approach is proposed to resolve the aliased raw data in elevation. Taking established full-link raw data simulation and imaging processing models, the impacts of azimuth signal reconstruction and elevation DBF processing on system performances are deeply analyzed. Finally, based on our airborne SAR system, the airborne SAR experiment is established, and processing results on the raw data from the experiment SAR system will be used to validate advanced spaceborne SAR concepts and their corresponding signal processing approaches.

基于捷变PRF新体制星载合成孔径雷达（SAR）技术在星载高分辨宽幅的成像方面具有重要应用前景。本项目系统地研究了捷变PRF体制的工作机理和性能。结合条带和滑动聚束模式，本项目构建了高分辨宽幅测绘模式；通过深入研究捷变PRF体制下回波信号特征，分析捷变PRF非均匀采样与多普勒频谱混叠的耦合问题，提出相应的解决方法；同时针对距离向回波信号混叠问题，提出一种采用改进的数字波束形成(DBF)技术的回波接收方法；本项目建立了全链路回波模拟与成像处理模型，深入研究方位信号重建和距离向DBF处理对系统性能的影响；依托本单位机载实验平台，完成相应的机载校飞实验，进一步验证该新体制星载SAR技术及其相应的信号处理方法的正确性。

分辨率和成像幅宽是星载合成孔径雷达（SAR）两项重要的技术指标。受星载SAR脉冲成像体制、最小天线面积约束、卫星资源等方面的限制，分辨率和成像幅宽无法在传统技术条件下得到同时提高。本项目围绕捷变PRF技术，重点研究了捷变PRF技术在高分宽测条带和滑动聚束模式下的应用，分析了各种模式下的回波信号特征，并根据回波信号特征提出了相应的信号处理方法。对于捷变PRF技术在条带式SAR中的应用，推导了周期线性变PRI时的回波特征，给出了PRF变化方案设计流程图来确定PRF变化范围和一个变化周期内的脉冲个数。得到的回波在方位向为周期非均匀采样信号，提出一种改进的多通道重建算法来恢复均匀采样信号。此外，针对捷变PRF条带模式下多个子测绘带回波混叠的问题，提出了一种基于距离向数字波束合成（DBF）的回波分离方法。对于捷变PRF技术在斜视聚束式SAR中的应用，根据参考中心的斜距变化推导和提出了对应的PRF变化方案，以消除距离单元徙动对测绘带宽的影响。获取的回波数据在方位向为非周期非均匀采样信号，提出利用一种改进的时域后向投影算法对该非均匀采样数据进行成像。依托本单位多功能机载SAR校飞试验系统，利用机载校飞试验数据和地基试验数据来完成对信号处理方法的原理性验证，为捷变PRF技术在下一代星载SAR系统上的应用奠定一定的理论和技术基础。