Antenna Subsystem

The antenna subsystem is a critical element of spacecraft design. If the spacecraft antenna can be made sufficiently large, higher antenna gain can be achieved, reducing the amount of RF power that must be generated on board to deliver a given power density at Earth-station antennas. Alternatively, for a fixed level of on-board power, higher-gain spacecraft antennas permit the use of smaller Earth-station antennas or enable higher data rates for a given antenna size.

Large antennas, however, present significant structural and mechanical challenges. They must be stowed within the launch vehicle fairing and reliably deployed once in orbit, which increases design complexity and risk.

To increase the power density delivered to a particular community of Earth stations, the satellite must be able to concentrate its radiated power over the geographic region occupied by that community. At a minimum, this requires antenna directivity sufficient to illuminate the Earth’s visible disc, which subtends an angle of approximately 17.34° as seen from geostationary orbit. In addition to these Earth-coverage antennas, modern satellites commonly employ more narrowly focused beams, achieved either through multiple antennas, shared reflector systems with offset or clustered feeds, or dedicated multibeam antenna architectures.