Use of shaped lens to control spillover in reflector antennas

In the design of reflector antenna systems, the control of sidelobes caused from spillover of the primary pattern presents a major design challenge. The design of the illumination pattern of the reflector system is the key to designing a reflector system that optimizes gain while minimizing the level of the sidelobes. The reduction of spillover sidelobes requires the use of large aperture feeds that provide a highly tapered illumination pattern. One of the traditional methods for accomplishing this design is the use of large aperture conical or corrugated horns for the feed. These designs are extremely effective for single band feeds but present problems when needed to operate over an extended frequency band. The approach presented in this paper attempts to illustrate a broadband solution to the feed pattern shaping design. The use of a doubly shaped lens placed at the aperture of a multi-band feed is investigated. The investigation is performed on a parabolic antenna system. The first surface of the lens transforms the radiation pattern into a plain wave exiting the feed aperture. The second surface then refocuses the radiation to the focal point of the reflector´s parabolic surface. This approach allows greater control of the primary pattern and allows the illumination pattern to be optimized for the antenna system design