Beam Forming Network for a Multibeam Antenna at 20 GHz

A multibeam antenna, which generates 115 Area Beams for European Continuous Coverage and 12 City Beams to cover 12 main ground stations, has been defined. Area and City Beams are generated by the same array of feeds and are isolated through polarization discrimination. On both, frequency reuse, through spatial separation, is applied. Furthermore, the central ground station provides a 27 GHz beacon signal for RF Sensing. For the isolation objectives (30dB) achievement, each City Beam is generated by a cluster of seven feed elements, part of which is shared between two adjacent beams. The feeding of the cluster and the sharing are performed by a Beam Forming Network (B.F.N.), in rectangular waveguide. The paper describes the B.F.N. components and their computed electrical performance, compared with the results measured on a partial B.F.N. breadboard. A good agreement and a flat behaviour of the B.F.N., in more of 10% bandwidth, is shown.