An influence on radiation characteristics by FSS on a beam‐waveguide feed with FSS

Abstract

AbstractDual reflector antennas fed with a beam waveguide are widely used for base stations of satellite communication and for radio astronomy. When the antenna is used at several frequencies, it is effective to carry out diplexing with a frequency selective surface (FSS) in the beam waveguide. Traditionally, when an antenna containing an FSS on the reflector surface is designed, or its radiation characteristics are evaluated, it is assumed that the FSS is ideal and it is modeled by a metal plate or a transparent plate in order to derive the radiation characteristics of the antenna at the frequency range in which the FSS is used for transmission or reflection. Next, the return loss or transmission loss of the FSS alone is derived. This loss has been considered as gain reduction of the radiation characteristics of the antenna with an ideal FSS. However, since the reflection and transmission characteristics of the FSS differ depending on the angle of incidence and polarization angle of the wave incident on the FSS, the radiation pattern of the entire antenna system and that of the wave that is incident on the focusing reflector connected to the FSS are different from those obtained when using a focusing reflector modeled by an ideal FSS. Hence, for accurate design and evaluation of a dual reflector antenna fed by a beam waveguide using an FSS, the effect of the reflection and transmission characteristics of the FSS on the radiation characteristics must be considered in addition to the loss caused by the FSS. This paper studies the effect of the FSS on the radiation characteristics when a dual reflector fed by a beam waveguide with an FSS partially installed is excited by the fundamental mode (EH11) of the primary radiator. For calculation of the electromagnetic field in the beam‐waveguide feed, the beam mode expansion method is used, so that the wave effect is taken into account. For calculation of the reflection and transmission characteristics of the FSS, a simple method is used in which the electromagnetic field scattered by the FSS is expanded in terms of Floquet modes and the electric field on the FSS is determined by the method of moments. Further, in order to reduce the effect on the radiation characteristics resulting from the difference in reflection phase at the metal part and at the FSS, the location of installation of the FSS is offset so that the phase difference of the reflected waves from two regions is compensated. This proposed method is found effective. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 21–31, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10041