基于相位编码CP-OFDM正交波形的SAR抗干扰研究
An Anti-Jamming SAR Method Based on Phase-Coded CP-OFDM Orthogonal Waveforms
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摘要: 随着数字化技术和雷达系统的发展,针对合成孔径雷达(Synthetic Aperture Radar, SAR)的干扰对抗技术不断进步,尤其是基于数字射频存储技术(Digital Radio Frequency Memory, DRFM)产生的有源欺骗干扰为SAR成像系统带来了前所未有的考验。针对欺骗干扰开展SAR成像抗干扰方法研究,本文基于相位编码波形与带有循环前缀的正交频分复用(Cyclic Prefix Orthogonal Frequency Division Multiplexing, CP-OFDM)波形进行正交波形设计,提出了相位编码CP-OFDM正交波形。基于CP-OFDM波形的循环前缀(Cyclic Prefix, CP)特征,引入基于线性模型的脉冲压缩方法对相位编码CP-OFDM正交波形的SAR成像回波进行距离向处理,能够实现无旁瓣干扰的自相关脉冲压缩。通过对相位编码CP-OFDM波形的时域相位进行编码优化设计,可以实现不同相位编码CP-OFDM波形之间良好的互相关性能。基于线性模型脉冲压缩方法改善了一种p范数多波形加权循环(p-norm Weighted Cyclic Algorithm, p-WeCAN)波形优化算法,采用该算法对相位编码CP-OFDM波形集的相位编码序列进行优化设计,优化后波形的互相关脉冲压缩结果的峰值水平(Peak Sidelobe Level, PSL)相比于随机相位编码CP-OFDM波形的互相关PSL改善了2 dB左右。CP特性赋予了相位编码CP-OFDM波形良好的自相关脉冲压缩结果,相位编码优化设计提供了良好的互相关脉冲压缩结果,采用该正交波形集进行SAR成像,能够实现对欺骗干扰的抑制。进行了点目标、面目标和基于GF-3回波数据反演的半实测数据的抗欺骗干扰SAR成像仿真,与基于线性调频(Linear Frequency Modulation, LFM)波形的欺骗干扰条件下的成像结果进行对比,验证了相位编码CP-OFDM对欺骗干扰的抑制能力。Abstract: 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.
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