Abstract: In radio telescope,the dual polarization and broadband design is used to improve surveying efficiency, and the multi beam technique is usually employed to widen the field of view and to increase the surveying speed. Multiple independent off focal feeds can form a multi beam reflector antenna. The multi feed per beam reflector antenna has a simple structure but stable performance within wide bandwidth. A dual polarization and broadband 19 beam feed for the five hundred meter aperture spherical telescope (FAST) is designed. Design method, designed and measured results are presented. Based on the primary amplitude and phase radiation patterns of the feed, the performance of the multi beam instantaneous parabolic reflector antenna deformed from an active spherical main reflector in real time is calculated, and the influence of the remaining spherical surface on the illuminated parabolic surface due to leakage energy is analyzed. This system level design method and design results provide design references and data references for the FAST reformation such as frequency band replacement in the future.

Key words: multi beam antenna, feed, broadband, dual polarization, radio telescope