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Channel Phase Mismatch Calibration for Multichannel in Azimuth SAR Imaging Based on Eigen-structure Method
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摘要: 作为实现高分辨率宽幅成像的重要技术手段之一，方位多通道合成孔径雷达(Synthetic Aperture Radar, SAR)近年来得到了广泛的研究与发展。在进行多通道数据重建之前，通道之间的传输特性必须校正一致，以避免图像中出现严重的虚假目标。在多通道SAR数据处理中，精确的基带多普勒中心估计对系统的通道失配校正和高分辨率成像具有非常重要的意义。但是单一通道数据的多普勒频谱混叠制约了传统基带多普勒中心估计算法在方位多通道SAR系统中的应用。基于特征分解处理，该文提出一种新的基带多普勒中心估计方法。该方法在推导过程中考虑了波束指向存在斜视的影响，能够实现方位多通道SAR系统基带多普勒中心和通道间相位误差的鲁棒估计。仿真实验和C波段方位向四通道机载SAR实验数据处理分析验证了算法的有效性。Abstract: As one of the most important means to achieve a High-Resolution and Wide-Swath (HRWS) imaging of the earth, multichannel in azimuth Synthetic Aperture Radar (SAR) have attracted considerable attention in recent years. However, prior to the unambiguous reconstruction of the multichannel SAR signal, each channel needs to be well calibrated, otherwise the performance of the reconstruction processor may degrade or even lose its effectiveness. Accurate baseband Doppler centroid estimation are critical for channel mismatch calibration and high-resolution imaging in the multichannel SAR systems. However, in the multichannel HRWS SAR system, the signal acquired by each channel is under-sampled that renders the traditional Doppler centroid estimation methods obsolete. In this paper, an eigen-structure method has been used to achieve a robust estimation of the baseband Doppler centroid and the phase mismatch in the multichannel SAR system. Processing with simulated and experimental C-band, four-channel airborne SAR data validates the effectiveness of this method.
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图 4 数据重采样过程(红色实心圆点表示原始多通道数据，黑色实心圆点表示重采样之后的多通道数据)
Figure 4. Process of resampling original experimental data (red solid dots represent original experimental data, and black solid dots represent resampled data)
图 6 C波段四通道机载SAR实验数据成像结果
Figure 6. Imaging results of the C-band four channel airborne SAR experimental data
表 1 星载仿真实验参数
Table 1. System parameters of simulated spaceborne experiment
系统参数 数值 通道数目 4 信噪比(dB) 40 轨道高度(km) 630 平台速度(m/s) 7545 载频(GHz) 5.4 发射信号带宽(MHz) 80 脉冲重复频率(Hz) 1257.5 多普勒带宽(Hz) 2515 
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表 2 仿真实验相位误差设置
Table 2. Phase mismatch set in simulated experiment
通道 相位误差(rad) 通道1 – 通道2 0.5 通道3 0.15 通道4 0.75
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表 3 仿真实验相位误差和基带多普勒中心估计结果
Table 3. Estimation of phase mismatch and baseband Doppler centroid in simulated experiment
通道 相位失配(rad) 基带多普勒中心估计(Hz) 预设 估计 预设 估计 通道1 – – – – 通道2 0.50 0.4999 100 100.85 通道3 0.15 0.1496 100 100.64 通道4 0.75 0.7495 100 100.25
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表 4 C波段方位向四通道机载SAR实验参数
Table 4. Experimental parameters of C-band azimuth four channel airborne SAR system
系统参数 数值 通道数目 4 平台高度(m) 8600 平台速度(m/s) 129.64 载频(GHz) 5.4 发射信号带宽(MHz) 210 方位向天线尺寸(m) 0.624 脉冲重复频率(Hz) 137.19
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表 5 C波段四通道机载SAR实验数据处理结果
Table 5. Experimental results of C-band four channel airborne SAR system
通道 相位失配(rad) 系统多普勒中心(Hz) 通道1 – – 通道2 1.058 –34.57 通道3 0.994 –34.18 通道4 1.577 –34.29
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