A satellite is a radio relay station in orbit above the earth that receives, amplifies and redirects analog and digital signals contained within a carrier frequency. They are of three types. Geostationary (GEO) satellites are in orbit 22282 miles above the earth and rotate with the earth, thus appearing stationary. The downlink from GEOs to earth can be localized into small regions or cover up as much as a third of the earth's surface. Low-earth orbit (LEO) satellites reside 1000 miles above the earth and revolve around the globe every couple of hours. They are in view for a few minutes, and multiple LEOs are required to keep continuous coverage. Medium-earth orbit (MEO) satellites are in the middle, taking about six hours to orbit the earth and can be viewed for a couple of hours.
The first communications satellite was launched in 1960 and it was an instrumented inflatable sphere which just reflected radio signals back to the earth.
Semiconductor quantum dots, which cover almost completely the entire spectral region from the ultraviolet to the far infrared, with a small number of substrate materials are suitable candidates in satellite communications. Further advantages of quantum dot lasers are small energy consumption through low threshold current densities, a high modulation range for high-speed applications as well as improved temperature stability. For example
InGaAs Quantum dot lasers are already commercialised in communication satellites. Ken Teo and his team at the University of Cambridge have come up with a much more efficient and compact way to send signals from satellites. They have managed to use an array of carbon nanotubes to create a device that replaces conventional heavy, bulky, high temperature, microwave amplifiers. The new electron source promises to revolutionize telecommunications and satellite communications in space.
Communication, especially to remote areas, is made possible with the use of satellite-based transmitters. There are typically 50 microwave amplifiers on board a satellite, each weighing about 1kg and measuring about 30 cm in length. Currently it costs about 10,000 pounds sterling to send a single kilogram of payload (data) into space. There is an advantage, both in terms of cost savings and extra payload that can be carried, if the weight and size of the microwave devices are reduced.
The first communications satellite was launched in 1960 and it was an instrumented inflatable sphere which just reflected radio signals back to the earth.
Semiconductor quantum dots, which cover almost completely the entire spectral region from the ultraviolet to the far infrared, with a small number of substrate materials are suitable candidates in satellite communications. Further advantages of quantum dot lasers are small energy consumption through low threshold current densities, a high modulation range for high-speed applications as well as improved temperature stability. For example
InGaAs Quantum dot lasers are already commercialised in communication satellites. Ken Teo and his team at the University of Cambridge have come up with a much more efficient and compact way to send signals from satellites. They have managed to use an array of carbon nanotubes to create a device that replaces conventional heavy, bulky, high temperature, microwave amplifiers. The new electron source promises to revolutionize telecommunications and satellite communications in space.
Communication, especially to remote areas, is made possible with the use of satellite-based transmitters. There are typically 50 microwave amplifiers on board a satellite, each weighing about 1kg and measuring about 30 cm in length. Currently it costs about 10,000 pounds sterling to send a single kilogram of payload (data) into space. There is an advantage, both in terms of cost savings and extra payload that can be carried, if the weight and size of the microwave devices are reduced.
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