The open cassegrain antenna: Part I. electromagnetic design and analysis

The open cassegrain antenna combines an asymmetric cassegrain reflector system with antenna rotation about two non-orthogonal axes. The compact configuration provides well-controlled radiation with full hemispheric coverage. A comprehensive analysis of the antenna geometrical and radiation characteristics has been made, and an experimental antenna with 40-inch aperture, operating at 60 gcs, has been constructed and measured electrically. Agreement was obtained between the computed and measured characteristics of the antenna and its components. By computation, it is found that the aperture efficiency of the experimental antenna is 70.4 per cent, the antenna efficiency (neglecting ohmic loss) is 65 per cent, and based on measured subreflector radiation patterns, the noise temperature due to spillover at the main reflector is less than 4°K.