Antenna payload design for advanced satcom satellites

Advanced Satcom Satellites require uplink (30 GHz) and downlink (20 GHz) antennas providing regional earth coverage (Canada, CONUS, Alaska, Hawaii and Puerto Rico) using high gain multiple overlapping spot beams. The antenna coverage with 128 beams that are arranged in a hexagonal grid fashion is shown in Figure 1. Critical antenna design parameters required for this system are very low scan loss over a ±9 beamwidths scan, maximum coverage area gain and moderate sidelobe isolation among alternate beams that reuse the frequency. In order to satisfy these requirements, a dielectric spherical lens antenna has been selected for both Tx and Rx antennas to take advantage of its excellent scan capabilities and its centre-feeding configuration. The radiation characteristics of the beams produced by such a lens using septet feed per beam on Rx and single feed per beam on Tx have been optimized and are presented here. The resultant beams show scan loss of less than 0.4 dB over the coverage region and meet the system requirements.