Design of double layers dichroic subreflector for S and X band Cassegrain antenna

This article demonstrates design of double layers dichroic subreflector for dual frequency cassegrain antenna. This dichroic subreflector is designed to be used in ground station antenna for simultaneous reception of data in S and X band from remote sensing satellites. This earth station antenna consists of X band feed at Cassegrain focus which necessitates a subreflector surface to be fully reflective in (8.0–8.5)GHz and S band feed at prime focus that requires subreflector to be transparent in (2.0– 2.3)GHz. The desired performance is achieved by placing two layers of dielectric sheets printed with copper rings and keeping an inter layer spacing of λ/4. A detail parametric analysis of the proposed design has been carried out to get an optimum performance in both the operating frequency bands. This dichroic subreflector offers minimum loss in S band, thereby maximizes the S-band G/T while degradation in performance in the X-band is negligible compared to solid metallic surface. To avoid the effect of angle of incidence adaptive element size is chosen.