|A radar system locates flying objects by sending out a signal (1) and picking up any signal reflected back (2). The radar dish (3) reflects the outgoing signal in an arc (4) and focuses the return signal (5) onto the receiver (6). The radar array rotates (7) to cover 360°. A computer processes the signal (8) and planes in range (9) show up as blips (10) on an operator's screen (11).
A radar (radio detection and ranging) system
that detects long-range objects and determines their position by measuring
the time taken for radio waves to travel to the objects, be reflected, and
return. Radar is used for navigation, air control, fire control, storm detection,
in radar astronomy, and for catching
speeding drivers. It developed out of experiments in the 1920s measuring
the distance of the ionosphere by radio
pulses. Robert Watson-Watt showed that
the technique could be applied to detecting aircraft, and from 1935 Britain
installed a series of radar stations which were a major factor in winning
the Battle of Britain in World War II. From 1940 the UK and the US collaborated
to develop radar.
- A method, system, or technique of using beamed, reflected, and timed radio waves for detecting, locating,
or tracking objects (such as rockets), for measuring altitude, etc.,
in any of various activities, such as air traffic control or guidance.
- The electronic equipment or apparatus used to generate, transmit,
receive, and, usually, to display radio scanning or locating waves;
a radar set. The terms primary radar and secondary
radar may be used when the return signals are, respectively,
by reflection and by the transmission of a second signal as a result
of triggering responder beacon by the incident signal. "Radar" is an
abbreviation of "radio detection and ranging."
There are two main types of radar: continuous-wave radar,
which transmits continuously, the frequency being varied sinusoidally, and
detects the signals received by their instantaneously different frequency;
and the more common pulsed radar. This latter has a highly
directional antenna which scans the area systematically or tracks an object.
A cavity magnetron or klystron
emits pulses, typically 400 per second, 1 μs across, and at
a frequency of 3 GHz. A duplexer switches the antenna automatically from
transmitter to receiver and back as appropriate. The receiver converts the
echo pulses to an intermediate frequency of about 30 MHz, and they are then
amplified, converted to a video signal, and displayed on a cathode-ray
tube. A synchronizer measures the time-lag between transmission and
reception, and this is represented by the position of the pulse on the screen.
Various display modes are used: commonest is the plan-position indicator
(PPI), showing horizontal position in polar coordinates.