Page 269 - Concise Encyclopedia of Robotics

RADAR R
Electromagnetic waves at radio frequencies (RF) are reflected from metallic
objects. The term radar is a contraction of the full technical description,
radio detection and ranging. Radar can be used by robots as a navigation
aid, and also for speed measurement.
A radar system intended for ranging and direction measurement
consists of a transmitter, a directional antenna, a receiver, and a position
indicator. The transmitter produces intense pulses of RF microwaves.
These waves strike objects. Some things (such as cars and trucks) reflect
radar waves better than others (such as wood). The reflected signals, or
echoes, are picked up by the antenna. The farther away the reflecting
object, the longer the time before the echo is received. The transmitting
antenna is rotated so that the radar sees in all directions.
As the radar antenna rotates, echoes are received from various direc-
tions.In a robot,these echoes are processed by a microcomputer that gives
the machine a sense of its position relative to the work environment.
Radar can be used by robotic aircraft and spacecraft.
A special form of radar, called Doppler radar, is used to measure the
speed of an approaching or retreating target, or the speed of a robot with
respect to a barrier. This type of radar operates by means of the Doppler
effect, as shown in the illustration on page 254. This is how police radar
measures the speed of an oncoming vehicle. Compare LADAR and SONAR.
See also COMPUTER MAP, DIRECTION RESOLUTION, DISTANCE RESOLUTION, and RANGE
SENSING AND PLOTTING.
RADIANT HEAT DETECTOR
See PRESENCE SENSING.

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