We have studied microwave diffraction by plane, conducting screens having rotational symmetries about their axes. The dimensions of the objects were of the order of a wavelength. Sample shapes were, for twofold symmetry, a rectangle; for threefold symmetry, a triangle; for fourfold symmetry, a square, cross, and cuspate figure; and for fivefold symmetry, a pentagon. The measurements of intensities were taken along the axes of the objects on the shadow side with the electric dipole probe parallel to the incident electric field. For objects of three- or more-fold symmetry, the observed intensities were independent of the orientation of the object about its axis. Only for the object of twofold symmetry was the intensity dependent on orientation. For scattering objects of the order of a wavelength in dimensions, and for which exact electromagnetic theory solutions have never been obtained, this is a useful generalization. We have presented an elemental model to explain the independence of intensity upon the rotation of the screens of three- or more-fold symmetry, as well as the unique behavior for twofold symmetry.
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