18WuD2x

150 corner reflector • corrosion-resistant
corner reflector, 2
high and microwave frequencies for television reception
and satellite communications. Sometimes
several half-wave dipoles are fed in phase
and arranged along a common line with a single,
elongated reflector. 2. Also called tricorner reflector.
A set of three flat metal surfaces or screens,
attached together in a manner identical to the
way two walls meet the floor or ceiling in a room.
Such a device, if it is at least several wavelengths
across, returns electromagnetic energy in exactly
the same direction from which it arrives. Devices
of this type are used as radar dummy targets and
in optical and infrared (IR) wireless ranging
systems.
corona A luminous discharge in the space surrounding
a high-voltage conductor; caused by
ionization of the air. The discharge constitutes a
loss of energy.
corona effect The production of a luminous discharge,
especially at the end of a pointed terminal,
when the voltage gradient reaches a critical
value.
corona failure A form of high-voltage failure, resulting
from the erosion of an object (such as an
electrical insulator) by corona.
corona loss Loss caused by energy dissipation
through a corona. It occurs as a result of the
emission of electrons from the surface of electrical
conductors at high potentials, and depends
on the curvature of the conductor surface, with
most emission occurring from sharp points and
the least from surfaces with a large radius of curvature.
It is often accompanied by a blue glow
and a crackling or hissing sound.
corona resistance The length of time that an insulating
material can withstand a specified level of
field-intensified ionization before completely
breaking down.
corona shield A shield surrounding a high-voltage
point to prevent corona by redistributing the electric
flux.
corona starting voltage The minimum voltage between
two electrodes, or on a single electrode in
free space, at which corona occurs.
corona voltmeter A voltmeter used to measure the
peak value of a voltage in terms of corona discharge.
It consists of a metal tube in which a central
wire is mounted, the parts being connected to
the voltage source. The air density in the tube is
varied until corona occurs.
corpuscle A tiny particle. It was the name given to
the ELECTRON by some early experimenters and
theorists.
correction 1. The addition of a factor that provides
greater accuracy in a measurement. 2. A change
in the calibration of an instrument to increase the
accuracy.
correction factor A percentage, or numerical factor,
added to or subtracted from a reading to provide
a greater degree of accuracy. Often used with
instruments known to be inaccurate by a certain
amount.
corrective feedback Feedback that is used to correct
(bring to a prescribed level) a quantity constituting
the input to a system.
corrective maintenance The repair of a circuit or
system after it has malfunctioned or broken
down.
corrective network A network that improves the
performance of the circuit into which it is inserted.
corrective stub A combination tuning-matching
stub used in some antenna systems. It matches
the resistive component of the antenna impedance
to the characteristic impedance of a feed
line, and also eliminates any reactance that
might be present at the antenna feed point.
correed relay A sealed reed relay used as a highspeed
switching device in communications equipment.
correlation A statistical expression or measure of
the degree to which two sets of data are related.
Can be given qualitatively (high-positive, lowpositive,
zero, low-negative, or high-negative) or
quantitatively (as a number between –1 and 1).
Does not necessarily imply causation.
correlation detector A detector that compares a
signal of interest with a standard signal at every
point, delivering an output that is proportional to
the correspondence between the two signals.
correlation distance The smallest distance between
two antennas that results in fading of signals under
conditions of tropospheric propagation. It is
used at very-high frequencies (VHF) and above, to
determine the maximum range over which communications
can be carried out reliably.
correlation tracking A method of target tracking
in which phase relationships are used to determine
positions.
correspondence The ability of a binocular machine
vision system to tell when both of its optical
sensors are processing an image from the same
object; also, the ability of the system to keep both
sensors tracking the same object.
corrosion-resistant Pertaining to materials that
are treated to be immune to corrosion by the elements.
Such substances are preferable for use in
marine or tropical environments, where corrosion
is especially severe.