Onboard array-fed reflector antenna for 21-GHZ-band direct broadcasting satellite

Satellite broadcasting in the 21-GHz band is expected to broadcast wide-band programs such as Super Hi-Vision, which is ultra-high-definition with more than 4000 scanning lines. The 21-GHz band, however, suffers from heavy rain attenuation about three times more than that of the 12-GHz band in terms of decibels. This paper describes a mitigation technique using onboard array-fed reflector antennas that can boost the radiation power only in the areas with heavy rainfall, while keeping a constant level of radiation power in the rest of the service area. The electrical performance of miniature TWTs is also described. Furthermore, we evaluated the power efficiency of the array feed and this is also discussed.