Satellite Earth Station Antenna Systems and System Design

This chapter reviews the design and operation of user antennas for satellite communications – for fixed, mobile, and broadcast services. This review includes simple dipole antennas and progresses to Yagi-Uda antennas and then on to high-gain parabolic reflector antennas that are the most commonly used in satellite communication systems. The trade-off between antenna gain and beamwidth is explored in detail. The key differences in the design process for very small aperture terminals (VSATs) and large earth stations are explained. The influence of blockage on whether to choose offset-fed antennas over on-axis fed antennas is seen to be key. This is particularly true for small aperture antennas with diameters of less than 100 wavelengths. Frequency reuse through dual-polarization operation is presented, with the different system advantages of dual-linear and dual-circular operation set out. The impact of the choice of modulation on the power margins required for a given bit error rate (BER) is seen to be significant. Noise temperature contributions from the atmosphere, from the ground, and particularly from lossy-feed runs that reduce antenna performance are explored. Reducing the feed losses is key to the design of very large earth station antennas. The difference in the impact of noise temperature on the uplink and the downlink is explained, and the differences between antenna design and performance with regard to fixed-satellite service, mobile satellite service, and broadcast satellite services are noted. Finally, some additional aspects of earth station designs that are affected by the environment, both meteorological and interference, are discussed.