Types of earth station

Many different types of earth stations are required for satellite communications.The size of the earth station’s antenna is the primary feature distinguishing one earth station from another. The types are grouped under three
headings: long earth station, short earth station, and very small aperture VSAT  earth station.
Earth stations with large antennas 10 to 60m in diameter are called long earth stations. This type is often required to provide for high-capacity telephone, data, or television transmission. In general, the larger the antenna,the greater the traffic capacity of the station.

Small earth stations are antennas with diameters between 1 and 10 m. They are commonly sighted on the roofs or in the gardens of domestic and commercial buildings. Small earth stations provide capabilities for reception
of broadcast television and=or connection for thin-route telephony systems in remote regions.
Very small aperture (VSAT) earth stations are networks of satellite earth terminals, each of which has an antenna diameter between 0.3 and 0.9 m: hence the name ‘‘very small.’’ VSAT networks are usually arranged in a star
configuration in which small aperture terminals each communicate via the satellite to a large central earth station known as a hub station. Any aperture smaller than VSAT is called an ultra-small aperture terminal (USAT ).

Nearly all earth station antennas with a diameter greater than 4m are of the paraboloidal-reflector Cassegrain type has the following advanatages :

Greater electrical design flexibility, which allows aperture illumination efficiency to be maximized

Feed is easily accessible and connectable to LNAs and HPAs

Primary spillover is normally directed toward clear sky, which picks less noise than the conventional parabolic configurations

Operational flexibility, particularly in moving the antenna easily in either azimuthal and elevation directions.