Microwaves And Satellite Communication

Micro is a unit for measurement of length. As the name suggests microwaves are the portion of the electromagnetic spectrum where the wavelength falls between about one millimeter and thirty centimeters that is micrometers.

Frequency of microwave bands extends from about one gigahertz to three hundred gigahertz and is useful for short range, high reliability radio and television links. Systems which use microwave frequencies are radar, mobile radio, satellite communications, terrestrial line of sight and troposphere links.

An essential property of microwaves is that they travel in straight lines through the atmosphere, are not affected by the ionized layers. Also these waves are very less affected by temperature inversions and scattering. But these weather effects limit the distance between the transmitter and the receiver to a few miles. This problem is over come by usage of repeater stations placed along the propagation path that extend the distance over which communication can occur.

Basically a microwave repeater is a receiver/amplifier/transmitter combination used for relaying microwave signals in long distance and overland communication links. As frequencies of the signals increase thereby distance between repeaters decrease.

Main mode of propagation in the microwave range is line of sight. Line of sight means that the transmitter and receiver need to see each other. Thus range of line of sight communication depends upon the height of the communicating 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 quantizes of voice and data traffic and are subject to transmission impairments thus limiting the distance between relay points. Majority of the radio link systems carry analog signals which are frequency modulated, while a few carry digital signals. Radio link systems which are terrestrial are highly directional and send point to point voice and data signals.

Like television broadcast systems, satellite radio link systems also offer multiple path transmission for various signals. Waveguides are main transmission media for transmission of frequencies in the microwave spectrum. The walls of waveguides are highly polished and sometimes specially plated to reduce resistance and consequently power losses. These devices are constructed of brass, copper or aluminum and are made in sections of various lengths. The sections are straight, bent, twisted or flexible. The most common form of waveguide is rectangular in cross section although round waveguides may be used.

Microwaves can be transmitted by co axial cable, micro strip, strip line and optical fibers as well within certain range. Among these transmission of light modulated signals through optical fibers is the model method. As the waveguides provide excellent shielding and low loss so they can transmit greater amounts of power with less energy loss than co axial cables.