Microwave communication
Microwave
transmission refers to the technology of transmitting information or energy by
the use ofelectromagnetic waves whose wavelengths are conveniently measured in
small numbers of centimetre; 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
wavelength allows 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 spectrum below 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.
The next
higher part of the radio electromagnetic spectrum, where the frequencies are
above 30 GHz and below 100 GHz, are called "millimeter waves" because
their wavelengths are conveniently measured in millimeters, and their
wavelengths range from 10 mm down to 3.0 mm. Radio waves in this band are
usually strongly attenuated by the Earthly atmosphere and particles contained
in it, especially during wet weather. Also, in wide band of frequencies around
60 GHz, the radio waves are strongly attenuated by molecular oxygen in the
atmosphere. The electronic technologies needed in the millimeter wave band are also
much more difficult to utilize than those of the microwave band.
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