An Improved Antenna for Microwave Radio Systems Consisting of Two Cylindrical Reflectors and a Corrugated Horn

An Improved Antenna for Microwave Radio Systems Consisting of Two Cylindrical Reflectors and a Corrugated Horn By C. DRAGONE (Manuscript received January 31, 1974) A broadband antenna is described with an elliptical beam suitable for efficient illumination of the United States from a satellite in synchronous orbit. The antenna is also suitable for use in terrestrial radio systems above 10 GHz. It consists of a corrugated feed and two parabolic cylinders that efficiently transform the circularly symmetric beam radiated by the feed into an elliptical beam. Depolarization of the incident beam by the two cylinders is very small and essentially independent of the angle of incidence, which can therefore be chosen as large as required to avoid aperture blockage. The performance is described of an antenna with a 5.8° X 2.9° elliptical beam at 18.5 GHz. For any input polarization, the cross-polarized component of the far field remains over the entire beam at least 88.5 dB below the main component on axis. This cross-polarized component is due in part to imperfections in the corrugated feed and in part to some aperture blockage by the feed and depolarization by the cylinders. A first-order analysis of the frequency dependence shows that the beamwidths vary little with frequency for an antenna using a properly designed feed and cylinders of sufficiently large apertures. As the frequency is increased from 18.5 to 29 GHz, the measured horizontal and vertical beamwidth variations are +2.7 and --14 percent, respectively.