A note on the asymptotic physical optic solution to the scattered fields from a paraboloidal reflector

The asymptotic physical optic (APO) formulation for the scattered fields from a paraboloid has been found to give results which agree with experiment except in the rear region. The disagreement here is due to the inexact nature of the assumed geometric optic (GO) edge currents as used in APO. A means of correcting for the error in these currents is given here by appealing to the equivalent half plane problem of Sommerfeld. This correction method is called CAPO ("corrected" APO). The resulting corrected diffraction coefficients are shown to be numerically indistinguishable from those of GTD. Comparisons of predicted E - and H -plane field patterns, based on these corrected results, with measurements in the rear region are given and shown to be quite acceptable; the corrections having negligible effect elsewhere. The "static" nature (in the sense of implicitly ignoring slope diffraction) of APO, GTD, and CAPO is discussed.