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The
term
'radar'
refers to
a system that transmits electromagnetic waves and analyzes their
reflections to detect an object, as well as determine the object's
distance, altitude, direction, and speed. Radar can detect and
range either a stationary or a moving object. Although
it is now a standard English word,
'radar'
was originally coined in 1941 as an acronym for
"Radio Detection and Ranging".
A typical
radar system has a transmitter, a receiver, an antenna, a waveguide
that links the transmitter to the antenna, a duplexer that allows
the antenna to be used for both transmitting and receiving, and an
electronic control system. The receiver is usually in the same
location as the transmitter, although not always.
The
transmitter sends out electromagnetic waves that are in phase and
usually of microwave or radio frequencies. When these waves
hit an object in their path, they scatter in different directions.
Some of these waves are reflected back and reach the receiver of the
radar system through the antenna. Modern radar antennas are usually
equipped with a parabolic dish to make the transmitted beam tighter
and more directional. This dish can be auto-steered to have a
'radar lock' on an object if it is used with two radar frequencies.
The
reflected signals, which are weak when received, are then amplified
to facilitate their further processing. The reflected signals
are then analyzed in relation to the transmitted signals. By
measuring the time it took for the transmitted signal to be
reflected back to the radar system, the distance of the object
detected can be computed. Differences between the frequencies of the
transmitted and received signals can also be analyzed to determine
the speed of the object.
Radar is
used in a variety of applications: military intelligence, traffic
control (land, sea, and air), meteorological detection of
precipitation, measurement of waves on the ocean surface, etc.
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Figure 1. A radar system with a parabolic dish
antenna. |
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