GTD analysis of near-field and far-field patterns of a parabolic subreflector illuminated by a plane wave

A geometrical theory of diffraction (GTD) analysis of the principal plane far-field and near-field patterns of a near-field Cassegrainian subreflector is presented. The uniform geometrical theory of diffraction (UGTD) [1] that drastically reduces the computation time has been utilized to analyze the subreflector in the form of a paraboloid illuminated by a plane wave. The numerical computations of the far-field amplitude and phase patterns of a typical paraboloidal subreflector based on the above technique correlate well with the results obtained by physical optics current integration, justifying the validity of the analysis presented. The GTD near-field analysis presented here is an improvement over that published earlier [2] and removes some of its limitations.