Optimum Antenna Pointing for Eight-figure Satellite System

Abstract

We investigated the most suitable antenna pointing methods for quasi-zenith (eight-figure) satellites and their beam patterns. In this work, the beam pattern of the antenna is fixed in time and the antenna is moved as a whole. From the variation of the direction vectors from the satellite to 41 ground points distributed over inhabited regions in Japan, the optimum fixed beam pattern and the time variation of the antenna direction relative to the satellite body were derived. Population involved in each beam was taken into account and three types of satellite orbits were considered: (a) circular orbit, (b) elliptic orbit with apogee above the equator, and (c) elliptic orbit with the apogee at its north end. For the cases of (a) and (c), beams toward the most populated regions in Japan can be directed continuously with accuracy better than 0.01 [deg]. This means that the beam center reaches the ground within about 6 [km] from the target point. Therefore, the beams directed toward such regions need no mechanism to control the directions independently. In contrast, in locations near the edge of the service area, the error becomes about 0.1 [deg]. Since the distance between the beam center and the target point becomes comparable to the radius of the beam, beams directed toward such regions are required to have wider beam-width or mechanisms to control their directions. For the case (b), the error becomes more apparent. This is due to the large change in distance between the satellite and service regions.