Research on Synthetic Aperture FM-CW Imaging Radar Utilizing Polarimetry

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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.