DIFFRACTION ANALYSIS OF FREQUENCY-SELECTIVE REFLECTOR ANTENNAS

Frequency selective surface (FSS) reflector antennas are used in many dual-reflector antenna systems in order to provide multifrequency capa bilities. In the past, the diffraction analysis of reflectors was base d primarily on the assumption of a solid subreflector configuration an d only the gain loss caused by the presence of the FSS subreflector wa s accounted for. In this paper, a unified computational technique is p resented which allows the incorporation of the curved FSS geometry in the computation of the antenna radiation pattern. The scattered fields from an illuminated FSS reflector are formalized using Huygens' princ iple in such a way that the ''reflecting'' and the ''transparent'' FSS subreflector cases are treated identically and the thickness of the F SS subreflector remains arbitrary. The analysis utilizes local surface coordinates to describe the reflection/transmission matrices of the F SS subreflector where it is assumed that these matrices are available. In most cases one may use the local tangent plane for approximating t he plane of the FSS in the local coordinate surface of the reflector. The paper demonstrates how the local curved coordinate system can be i ntroduced in the diffraction modeling of FSS reflectors and its import ance in accurately predicting the side-lobe and cross-polarization lev els. Results of numerical simulations are presented for several FSS su breflector configurations.