Satellite communication systems are evolving to use higher and higher
frequencies. There are several reasons for this shift along the frequency
spectrum towards what is known as the EHF band. One of these is that the
lower end of the spectrum is already heavily used by other satellites
- there is little room for new broadcast and communications systems in
this territory.
The second reason has its roots in the burgeoning demand for high bandwidth
consumer services, such as videoconferencing and the internet. At higher
frequencies, bandwidth is wider and very high data rates of several hundred
mega bits per second become possible.
The ITALSAT F1 satellite was launched by the Italians in January 1991.
Its payload contains beacons that emit signals at EHF frequencies - 18.7,
40 and 50 GHz. Researchers monitored those beacon signals from a Ground
Station in Hampshire, gathering four years' of data. Once the STENTOR
satellite is launched in September 2002, the team will be able to collect
EHF propagation data from a ground station located in a tropical area.
Researchers use the data gathered to test the viability of high data transmission
rates. By measuring how much the signals from the beacons fade in bad
weather, researchers can build better computer models to predict how much
high frequency signals from the next generation of communications satellites
will fade across the globe.
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