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Range Ambiguity Suppression Approach for Quad-pol SAR Systems Based on Modified Azimuth Phase Coding
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摘要: 传统全极化SAR系统交叉极化通道由于受到强同极化距离模糊信号的干扰，使得交叉极化通道的距离模糊性能急剧下降，这严重限制了全极化SAR系统的测绘带宽。该文首先介绍一种扩展的极化发射体制—混合极化模式，该模式在改善交叉极化距离模糊性能的同时恶化同极化距离模糊性能。因此，为了更好地提高全极化SAR系统的距离模糊性能，该文提出一种改进的方位相位编码方法(MAPC)。该方法通过对系统发射脉冲进行调制解调，能够将全极化SAR系统的距离模糊能量转移到方位向，然后利用方位向维纳滤波器滤除距离模糊能量。该文的实验结果表明MAPC技术能够有效地去除全极化SAR系统的距离模糊能量，并扩展系统的无模糊测绘带宽。Abstract: For conventional quadrature-polarimetric (quad-pol) Synthetic Aperture Radar (SAR) systems, as cross-polarized (cross-pol) channels are influenced by the strong co-polarized (co-pol) range ambiguous returns, the range ambiguity levels of cross-polchannels are markedly reduced, which severely restricts the unambiguous swaths. A novel transmission scheme called a hybrid-polarimetric (hybrid-pol) mode is introduced to enhance the range ambiguity levels of cross-pol channels. This scheme improves the performance of cross-pol channels with regards to range ambiguity but deteriorates that of co-pol channels. Therefore, to further enhance the range ambiguity levels of quad-pol SAR systems, the Modified Azimuth Phase Coding (MAPC) technique based on hybrid-pol SAR systems is proposed in this study. By taking advantage of the MAPC modulation/demodulation, the power of range ambiguities is transferred to the azimuth that is filtered by an optimized Wiener filter in the Doppler domain. The simulation results validate that the MAPC technique can markedly eliminate the range ambiguity of quad-pol SAR systems and extend the unambiguous swaths.
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图 4 APC方法M=2时方位向多普勒频谱示意图
Figure 4. Doppler spectrum after APC modulation and demodulation (M=2)
图 5 全极化SAR系统中MAPC的发射调制方式
Figure 5. Modified APC modulation based on quad-pol SAR systems
图 7 L波段不同工作模式下同极化通道与交叉极化通道的RASR曲线
Figure 7. RASR of cross-pol and co-pol channels for L-band SAR systems based on different transmission mode
图 8 矩形滤波与维纳滤波时信号与模糊能量损失比
Figure 8. Compares filtering performance of rectangular filter and azimuth Wiener filter
图 9 MAPC方法对同极化通道与交叉极化通道RASR影响
Figure 9. Compares RASR of HH and HV-pol channel by using MAPC technique based on rectangular filter/azimuth Wiener filter
表 1 L波段全极化SAR系统参数
Table 1. Parameters for system examples
参数 数值 发射信号载频(GHz) 1.26 发射脉冲宽度(us) 70 平台高度(km) 607 系统多普勒带宽(Hz) 1235.9 发射信号带宽(MHz) 140 俯仰角(°) 35 平台飞行速度(m/s) 7500 天线高度(m) 2.9 
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