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Radar cross section enhancement for radar navigation and remote sensing Michelson, David George


Recent developments in radar navigation and remote sensing have led to a requirement for rugged yet inexpensive location markers and calibration targets which present both a very large scattering cross section and a specified polarization response over a wide angular range. This study considers several problems related to the analysis and design of passive radar targets derived from corner reflectors. Transformation of the polarization response of a target between global and local coordinate frames is shown to correspond to rotation of the polarization basis by a prescribed angle which is a function of both the coordinate transformation matrix and the direction of propagation. Once the angle of rotation has been determined using either spherical trigonometry or vector algebra, any polarization descriptor can be transformed between coordinate frames by application of a suitable rotation operator. The scattering cross section and angular coverage of a conventional trihedral corner reflector can be altered by modifying the size and shape of its reflecting panels. A numerical algorithm based on physical optics is used to predict the contribution of triple-bounce reflections to the response of a reflector with polygonal panels of arbitrary shape. If three-fold symmetry is broken and the reflector is simply required to present bilateral symmetry, it is found that the scattering cross section, elevation beamwidth, and azimuthal beamwidth of the reflector can be chosen independently of each other. A method for altering the polarization response of a conventional trihedral corner reflector by adding conducting fins or corrugations to one its interior surfaces is proposed. In calculating design curves for twist-polarizing or circularly polarizing reflectors by mode-matching, optimum accuracy and efficiency are obtained by setting the ratio of free space to groove modes equal to the ratio of groove width to the period. Methods for obtaining linear and circular polarization selective responses are considered. The contribution of triple-bounce reflections to the response of such reflectors is a function of the direction of incidence, the orientation of the reflector, the dimensions of the corrugations, and the size and shape of the reflecting panels. Experimental results show that prototype twist-polarizing and circularly polarizing reflectors respond essentially as predicted.

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