Microwave
Microwave frequencies range from 300 MHz to 30 GHz, corresponding to wavelengths of 1 meter to 1 cm. These frequencies are useful for terrestrial and satellite communication systems, both fixed and mobile. In the case of point-to-point radio links, antennas are placed on a tower or other tall structure at sufficient height to provide a direct, unobstructed line-of-sight (LOS) path between the transmitter and receiver sites. In the case of mobile radio systems, a single tower provides point-to-multipoint coverage, which may include both LOS and non-LOS paths. LOS microwave is used for both short- and long-haul telecommunications to complement wired media such as optical transmission systems. Applications include local loop, cellular back haul, remote and rugged areas, utility companies, and private carriers. Early applications of LOS microwave were based on analog modulation techniques, but today’s microwave systems used digital modulation for increased capacity and performance.
Microwave transmission refers to the technology of transmitting information or power by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeters; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.
Microwaves are widely used for point-to-point communications because their small wavelengthallows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna. This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a very large information-carrying capacity; the microwave band has a bandwidth 30 times that of all the rest of the radio spectrumbelow it. A disadvantage is that microwaves are limited to line of sight propagation; they cannot pass around hills or mountains as lower frequency radio waves can.
Microwave radio transmission is commonly used in point-to-point communication systems on the surface of the Earth, in satellite communications, and in deep space radio communications. Other parts of the microwave radio band are used for radars, radio navigation systems, sensor systems, and radio astronomy.