A transmission is sent from a station on Earth to the satellite. This signal is called an uplink. The transmission has a powerful high frequency which is referred to as a "Gigahertz (GHz) range signal". The satellite, in orbit about the Earth, receives the signal and then transmits it back to earth stations. This transmission signal back to earth is called a downlink.
The coverage area of a satellite is
called the satellite's footprint. Only receiving stations within
this footprint can receive the satellite's signals.
Basic Elements of Satellite Communications Systems
These signals are only transmitted on certain frequency bands. The International Telecommunication Union based in Geneva, Switzerland, assigns the specific bands to be used. Each band consists of an uplink band and a downlink band.
The band's reception on Earth is subject to an inverse relationship between frequency and wavelength. When frequency increases, wavelength decreases. The larger the wavelength, the bigger the antenna (satellite dish) necessary to receive it.
The two bands used most frequently
are the C-band and the Ku-band. The C-band has an uplink frequency
of 6 GHz and a downlink frequency of 4 GHz. The minimum site of an
average C-band antenna is approximately 2 to 3 meters in diameter.
C-Band Satellite Antenna
The Ku-band has an uplink frequency of 14 GHz and a downlink
frequency of 11 GHz. Ku-bands can have much smaller antennas.
The smallest of these antennas can be 18 inches in diameter. This
is the type of antenna used with home entertainment satellite dishes.
Ku-Band Satellite Antenna