Microwaves And Satellite Communication
Micro is a unit for measuring length. As the name suggests microwaves are the portion of the electromagnetic spectrum where the wavelength is between about one millimeter and thirty centimeters that is micrometers.
Frequency of microwave bands extends from about one gigahertz to three hundred gigahertz and are useful for short range, high reliability radio and television links. Systems using microwave frequencies radar, mobile radio, satellite communications, terrestrial line of sight and tropospheric links.
An essential characteristic of microwaves is that they travel in straight lines passing through the atmosphere, is not affected by ionized layers. Again, these waves are very less affected by temperature inversions and proliferation. But these weather effects limit the distance between the transmitter and receiver to a couple of miles. This problem has been obtained by use of repeater stations placed along the propagation path that extends the distance over which communications may occur.
Basically a microwave repeater is a receiver / amplifier / transmitter combination used for relaying microwave signals over long distances and land communication links. As the frequencies of the signals thus increase the distance between repeaters decrease.
Main form of propagation in the microwave range is line of sight. Sight Line means that the transmitter and receiver must be able to see each other. Thus some sight communication depends on the height of the transmitting antennas and the nature of the terrain between them. Radio horizon limits the distance over which signals can be sent.
Microwave repeaters i.e. radio link systems carry large quantize of voice and data traffic and is subject to transmission impairments and thus reduce the distance between relay points. Majority of the radio link systems carry analog signals which is frequency modulated, while a few carry digital signals. Radio link systems, which are terrestrial are very directional and send point to point voice and data signals.
Like the television broadcast systems, including satellite radio link systems offers several path transmission of various signals. Waveguides are the main transmission media for transmission of frequencies in the microwave spectrum. The walls of the waveguides are very polished and sometimes specially plated to reduce resistance and hence power loss. These units are constructed of brass, copper or aluminum and is made in sections of various lengths. The sections are straight, bent, twisted or flexible. The most common form of waveguide is rectangular although round waveguides can be used.
Microwaves can be transmitted through common coaxial cable, micro strip, strip line and optical fiber, within certain range. Among these, transmission of light modulated signals through optical fibers is the model method. As waveguides provide excellent shielding and low loss so they can send larger amounts of power with less energy loss than co axial cables.
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