Antennas for the lstar satellite

摘要

The government of Laos with a group of private investors, called Asia Broadcasting and Communication Network Company Limited (ABCN), have purchased two satellites from Space Systems/Loral to provide satellite communications that will include direct to home (DTH) TV broadcast and VSAT across Asia Pacific. The satellites, LSTAR-1 and LSTAR-2, will be the most powerful satellites to be launched for DTH service in the region. Each satellite will be capable of transmitting as many as 200 digitally compressed video channels to users in the region, using terminals smaller than 50 cm. The first satellite LSTAR-1, will commence service in the winter of 1998 and LSTAR-2, the second satellite, will be in service in 1999. The antenna design for the LSTAR communication satellite uses all shaped Gregorian antenna designs. This provides the highest possible copolarization efficiency and the lowest cross polarization characteristics for this application. This paper will discuss the design criterion for the three coverage beams of this satellite, and will show the predicted performance for each antenna. The three coverages will be isolated from each other to implement frequency reuse by virtue of spatial diversity, and within each coverage, polarization isolation will be maintained to allow frequency reuse by polarization diversity. The design considerations to accommodate these features will be discussed. A discussion will be included of the shaped Gregorian antenna design and the applications for which it is best suited. Since the three coverage beams for this satellite will operate the downlink and uplink bands simultaneously in each oí the three antennas, design considerations to avoid undesirable Passive InterModulation (PIM) products will also be discussed.