The Short-Backfire Antenna: A Numerical-Physical Optics Study of Its Characteristics

摘要

A numerical-physical optics method is applied to study the circuit (impedance) and radiation characteristics of the short-backfire antenna. This radiator, developed through extensive experimentation by AFCRL, consists of a dipole exciter located between a large rimmed reflector and a small secondary reflector. It has wide bandwidth and high directivity comparable to sophisticated reflector antennas. In the numerical-physical optics method, the following steps are followed: (1) a set of coupled integral equations for the currents excited in the dipole and on the surface of the secondary reflector are formulated and solved numerically, assuming for this step that the large reflector is infinite; (2) the surface currents of the large reflector are approximated by a truncated form of those calculated for the infinite conducting sheet; (3) the radiation field maintained by the currents of the steps (1) and (2) is calculated; and (4) a diffracted field correction is made to account for the finite dimensions of the large reflector and its rim. This method has the advantage, relative to earlier studies, that it can successfully predict the antenna's circuit characteristics. Excellent results are obtained for both square and circular geometries. Comparison is made with experimental measurements made by AFCRL. (Author)