An Anti-Jamming SAR Method Based on Phase-Coded CP-OFDM Orthogonal Waveforms

With the development of digital technologies and radar systems， jamming techniques against synthetic-aperture radar （SAR） have undergone rapid advancement. In particular， deceptive jamming based on digital radio frequency memory （DRFM） poses an unprecedented challenge to SAR imaging systems. In this study， an anti-jamming SAR imaging method is investigated to counter this technique by integrating phase-coded waveforms with cyclic-prefix orthogonal frequency-division multiplexing （CP-OFDM）. A pulse compression method based on a linear model is introduced in the proposed phase-coded CP-OFDM orthogonal waveform to perform range processing on SAR echoes with the phase-coded waveform based on the cyclic prefix （CP） property； this enables autocorrelation pulse compression free from inter-range cell interference. Optimization of the time-domain phase coding enables improved cross-correlation performance among different waveforms. A p-norm multi-waveform weighted cyclic algorithm （p-WeCAN） is improved using the pulse compression method based on a linear model to optimize the phase-coded sequences of the set of CP-OFDM waveforms. The optimized waveforms achieved a cross-correlation peak sidelobe level approximately 2 dB lower than that of a randomly phase-coded CP-OFDM waveform set. The CP ensures good autocorrelation pulse compression performance， while the optimized phase-coding design provides favorable cross-correlation characteristics. Thus， the orthogonal waveform set can suppress deceptive jamming effectively in SAR imaging. Simulations were conducted to evaluate the capability of the proposed approach to defeat deceptive jamming against SAR imaging for extended and point targets as well as complex scenes reconstructed from echo data collected by the Gaofen-3 satellite in comparison with those obtained using linear frequency modulation pulses， and the results verified the effectiveness of the proposed approach.

随着数字技术与雷达系统的发展，针对合成孔径雷达（synthetic-aperture radar，SAR）的干扰技术迎来了快速进步。其中，基于数字射频存储器（digital radio frequency memory，DRFM）的欺骗式干扰，给SAR成像系统带来了前所未有的挑战。本研究针对该干扰技术，提出了一种融合相位编码波形与循环前缀正交频分复用（cyclic-prefix orthogonal frequency-division multiplexing，CP-OFDM）的SAR抗干扰成像方法。在所提出的相位编码CP-OFDM正交波形框架中，引入了一种基于线性模型的脉冲压缩（pulse compression）方法，依托循环前缀（cyclic prefix，CP）特性对采用相位编码波形的SAR回波进行距离向处理，实现了无距离单元间干扰的自相关脉压。通过对时域相位编码进行优化，可提升不同波形间的互相关性能。基于该线性模型脉压方法，对p范数多波形加权循环算法（p-norm multi-waveform weighted cyclic algorithm，p-WeCAN）进行改进，以优化CP-OFDM波形集合的相位编码序列。优化后的波形集合，其互相关峰值旁瓣电平较随机相位编码CP-OFDM波形集合降低约2dB。循环前缀（CP）保障了优异的自相关脉压性能，而优化后的相位编码设计则提供了良好的互相关特性，因此该正交波形集合可有效抑制SAR成像中的欺骗式干扰。为验证所提方法的有效性，本研究开展了仿真实验：针对扩展目标、点目标以及基于高分三号（Gaofen-3）卫星采集的回波数据重建的复杂场景，与线性调频脉冲（linear frequency modulation pulses）方案进行对比，评估了所提方法对抗SAR成像欺骗干扰的能力，实验结果证实了该方法的有效性。