Elliptical beam closed-form dual-reflector antenna efficiently illuminated by a feed with an axially-symmetric radiation pattern

A dual-reflector antenna geometry is presented for allowing a quasi-elliptical aperture main reflector to be efficiently illuminated by an feed that radiates an axially symmetric pattern. The geometry works very well for apertures with axial ratios of 2:1 or less. The design is accomplished by the following steps. First, a subreflector surface is chosen that will spread the axially symmetric radiated energy from the feed unsymmetrically to the main reflector. Second, the main reflector surface is found, in closed form, from the law of equal optical path length. Third, a design procedure is developed that allows the user to find the sub and main reflector surfaces from basic input parameters such as the desired aperture and feed characteristics. Finally, a design example is presented to demonstrate the capability of the proposed geometry.