An important and widespread use of microwave engineering is communication satellite. What was the motivation? Telephone service overseas was exceptionally bad, and live television could not be received or transmitted over great distances. Properly positioned satellites could provide unobstructed communications for nearly all points on Earth as long as there was a method to put them in orbit. The key to this concept was the placement of space stations in geosynchronous Earth orbit (GEO), a location 35,786 kilometers (22,300 miles) above Earth. Objects in this orbit will revolve about Earth along its equatorial plane at the same rate as the planet rotates. Thus, a satellite or space station in GEO will seem fixed in the sky and will be directly above an observer at the equator. A communications satellite in GEO can "see" about one-third of Earth's surface, so to make global communications possible, three satellites need to be placed in this unique orbit (geostationary orbit).
Lets have some technical introduction to a communication satellite. A simple definition is: A set of radio receivers and transmitters (payload) based on a space-based platform (satellite bus/spacecraft) orbiting around the earth. Thus, the components of a communication satellite are Payload, Bus and Command & Control.
The satellite can have a passive role in communications like bouncing signals from the Earth back to another location on the Earth; on the other hand, some satellites carry electronic devices called transponders for receiving, amplifying, and re-broadcasting signals to the Earth. The area to which it can transmit is called a satellite's footprint.
Tidbit: Pakistan has a leased satellite, PAKSAT-1, in the 38 degree East longitude geostationary orbit. The government of Pakistan has granted approval for the replacement of PAKSAT-1 by a new communication satellite PAKSAT 1R by 2011. SUPARCO has also developed a prototype of a communication satellite named Prototype PAKSAT-1R and is now developing anEngineering Qualification Model (EQM) [4].
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