18WuD2x

34 antenna polarization • anthropomorphism
antenna polarization The orientation of electric
lines of flux, with respect to the surface of the
earth, for which an antenna is most efficient. A
vertical antenna radiates and receives vertically
polarized waves. A horizontal antenna radiates
and receives horizontally polarized waves broadside
to itself, and vertically polarized waves at
high elevation angles off its ends. In other directions,
the polarization is slanted at various angles.
antenna power Symbol, P ant . The RF power developed
in an antenna by a transmitter; P ant equals
I 2 R, where I is the antenna current and R is the
antenna resistance at point I is measured.
antenna power gain The ratio of the maximum effective
radiated power (ERP) from a wireless
transmitting antenna to the ERP from a reference
antenna, expressed in decibels (dB). If the ERP
from an antenna under test is P T watts and the
ERP from the reference antenna is P R watts, then
the gain G dB is:
G dB = 10 log 10 (P T /P R )
Power gain is always measured in the direction in
which the test antenna performs the best. The
reference antenna, usually a dipole, is chosen
with a gain assumed to be unity, or 0 dB. Gain
relative to a dipole is expressed in dBd (decibels
relative to a dipole). Alternatively, the reference
antenna can be an isotropic radiator, in which
case the gain is expressed in dBi (decibels relative
to an isotropic radiator). Gain figures in dBd and
dBi differ by a constant amount as follows:
G dBi = 2.15 + G dBd
antenna preamplifier A highly sensitive amplifier
used to enhance the gain of a receiver. It is usually
used at the very high frequencies and above.
antenna radiation The propagation of radio waves
by a transmitting antenna.
antenna radiator The element of an antenna that
receives RF energy from the transmitter and radiates
waves into space. Also known as the driven
element. Compare ANTENNA DIRECTOR and AN-
TENNA REFLECTOR.
antenna range 1. The frequency band, communication
distance characteristically covered, or
other continuum of values that specify the operating
limits of an antenna. 2. The region immediately
surrounding an antenna in which tests and
measurements usually are made. Sometimes
called ANTENNA FIELD.
antenna reflector In a directional antenna, a PAR-
ASITIC ELEMENT situated behind the radiator
and separated from the latter by an appropriate
fraction of a wavelength. Its function is to intensify
radiation in the direction of transmission.
Compare ANTENNA DIRECTOR and ANTENNA
RADIATOR.
antenna relay In a radio station, a low-loss, heavyduty
relay that enables the antenna to be
switched between transmitter and receiver.
antenna resistance The resistive component of
ANTENNA IMPEDANCE.
antenna resonant frequency The frequency, or
narrow band of frequencies, at which an antenna’s
impedance appears resistive.
antenna stage 1. The first RF amplifier stage of a
receiver. 2. Occasionally, the final RF amplifier of
a transmitter.
antenna switch In a radio station, a low-loss,
heavy-duty switch that enables the antenna to be
connected to transmitter, receiver, or safety
ground.
antenna system Collectively, an antenna and all of
the auxiliary electrical and mechanical devices
needed for its efficient operation, including couplers,
tuners, transmission lines, supports, insulators,
and rotator.
antenna terminals 1. The points at which a transmission
line is attached to an antenna. 2. The signal
input terminals of a receiver. 3. The signal
output terminals of a transmitter.
antennaverter An antenna and converter combined
into a single circuit, intended for connection
to the antenna terminals of a receiver to
allow operation on frequencies outside the band
for which the receiver has been designed.
antenna wire 1. The radiator element of a wiretype
antenna. 2. A strong solid or stranded wire
(e.g., hard-drawn copper, copper-clad steel, or
phosphor-bronze) used for antennas.
anthropomorphism The perception, by people, of
machines as having human qualities. This can