Research on Synthetic Aperture FM-CW Imaging Radar Utilizing Polarimetry

本研究旨在研制一种全极化二维合成孔径FM-CW成像雷达。本研究的主要目的是将雷达极化原理引入到宽带调频连续波雷达成像中。雷达极化测量是在雷达遥感中充分利用电磁波的矢量特性。单色波情况下的雷达极化测量已经建立，但对于FM-CW雷达而言，如何将其融合到宽带雷达信号中仍然是一个问题。在本研究中，我们指出，在FM-CW雷达系统中获得的拍频频谱可以作为一个散射矩阵元素来替代，它在雷达极化原理中起着重要的作用。由于合成孔径信号处理后的拍频频谱具有复杂的幅度(幅度和相位)，承载着极化目标的信息，因此它代表了目标与极化有关的散射特性。该值在扫频测量的中心频率处求值。研究了任意极化基下散射矩阵的变换，得到了目标特有的特征极化状态，从而获得了抗杂波的极化增强图像。利用放置在实验室中的线偏振基阵雷达，对平板、二面角反射器、导线、飞机模型等多个目标进行成像，以从散射矩阵中提取信息。事实证明，FM-CW雷达是一种新颖、全极化、高分辨率、革命性的成像雷达系统。

This research aimed at developing a full polarmetric and 2-dimensional synthetic aperture FM-CW imaging radar. The main purpose of this research was to introduce the principle of radar polarimetry into a wide-band FM-CW radar imaging. The radar polarimetry is a full utilization of the vector nature of the electromagnetic waves in radar remote sensing. The radar polarimetry has been well established for the monochromatic wave case, however, there still remains a question how to incorporate it into a wide band radar signal for the case of FM-CW radar. We pointed out in this research that the beat spectrum obtained in the FM-CW radar system could be replaced as a scattering matrix element which plays an important role in radar polarimetry principle. Since the beat spectrum after synthetic aperture signal processing has a complex amplitude (magnitude and phase) bearing polarimetric target information, it represents scattering characteristics of a target depending upon polarization. The value is evaluated at the center frequency of a swept frequency measurement. The authors investigated the transformation of scattering matrix in arbitrary polarization basis, which resulted in the derivation of the characteristic polarization states specific to a target, and polarimetric enhanced image against clutter. Using linear polarization basis configuration radar placed in a laboratory, several targets such as plate, dihedral corner reflector and wire, air-plane model were imaged to retrieve information from the scattering matrices. It was confirmed that the FM-CW radar acts as a novel, full polarimetric, high resolution, and revolutionary imaging radar system.