Development of a Multi-Shaped Beam Antenna in C-Band

This paper describes the development of a 4 GHz transmit antenna generating six shaped beams for covering main areas of Africa. Design and optimisation, hardware activities and performance data are presented. Two polarisation sensitive gridded single offset reflectors (diameter 2..15 m) are fed by two orthogonally polarised feed arrays with 16 and 20 feeds respectively. The antenna generates three independent beams for each polarisation. Frequency reuse by polarisation diversity and by space diversity between two far displaced beams allows for 30 channels in total to be transmitted. A flexible channel to beam allocation is possible (reconfiguration) with a slightly reduced channel number. The three horizontally polarised beams are partly overlappling with five of the 16 feeds to be shared. These feeds are excited via dual mode subnetworks. This feedsystem consisting of 16 compact, high efficiency SCRIMP-Horns, a dual mode beam forming network in barline technique has been manufactured and tested. Measurement results are compared with pattern predictions on the level of primary as well as secondary pattern. The correspondence is in both cases very close. Mutual. coupling between horns has been included exactly into the analysis. This is mandatory for a realistic cross-polar prediction as it is demonstrated by comparison with the measurements.