Page 54 - Electrical Engineering Dictionary

ANSI American National Standards In- the antenna structure and noise received by
stitute, a body which administers numerous the antenna from external radiating sources.
industrial standards in the USA including
several which pertain to electric utility con-
antenna pattern graph or chart repre-
struction practices. See American National
senting the absolute or normalized antenna
Standards Institute.
gain as a function of angle (typically azimuth
or elevation) and used to describe the direc-
antenna a device used to couple energy tional properties of an antenna. In the near
from a guiding structure (transmission line, field, the antenna pattern is a function of the
waveguide, etc.) into a propagation medium, distance from the antenna whereas in the far
such as free space, and vice versa. It provides field, the pattern is independent of distance
directivity and gain for the transmission and from the antenna.
reception of electromagnetic waves.
antennaQ ratiooftheenergystoredtothe
antenna beamwidth the effective an-
energydissipated(ohmicallyorviaradiation)
gular extent of the antenna radiation pattern
per cycle.
usually specified between points of fixed am-
plitude relative to the main lobe gain (e.g.,
−3 dB points). antenna synthesis the process of de-
termining or designing an antenna to yield
a given radiation pattern. Several synthesis
antenna diversity a diversity technique
methods exist. Some are closed form solu-
based on the use of multiple antennas either
tions and some use numerical techniques.
at the receiver (receiver antenna diversity) or
at the transmitter (transmitter antenna diver-
sity) in a radio communication link. If the anthropomorphic manipulator a ma-
separation of antennas is sufficient, the signal nipulator that consists of two shoulder joints,
components are affected by different fading one for rotation about a vertical axis and one
processes and are combined in the receiver for elevation out of the horizontal plane, an
to improve performance. See also RAKE elbow joint with axis parallel to the shoulder
receiver. Contrast with angle diversity. elevation joint, and two or three wrist joints at
the end of the manipulator (see figure). An
antenna gain the maximum ratio of an anthropomorphic manipulator is sometimes
antenna’s ability to focus or receive power in called a jointed, elbow, or articulated manip-
a given direction relative to a standard; the ulator.
standard is usually an isotropic radiator or a
dipole. The gain includes the efficiency of
the antenna.

antenna noise temperature the effective
noise temperature of the antenna radiation re-
sistance appearing at the antenna terminals.
At a given frequency, the antenna noise tem-
perature, T a ( K), can be calculated as P n
kB
where P n is the noise power available at the
antenna terminals (W), k is Boltzmann’s con-
0
stant (1.38×10 −23 J/ K), and B is the band-
width (Hz). The antenna noise is the result
of thermal noise generated in ohmic losses in
An anthropomorphic manipulator.

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2000 by CRC Press LLC