APPENDIX I
GLOSSARY
ABSORPTION—(1) Absorbing light waves. Does
not allow any reflection or refraction; (2)
Atmospheric absorption of rf energy with no
reflection or refraction (adversely affects long-
distance communications).
ACOUSTICS—The science of sound.
AMPLITUDE—The portion of a cycle measured from
a reference line to a maximum value above (or
to a maximum value below) the line.
ANGLE OF INCIDENCE—The angle between the
incident wave and the normal.
ANGLE OF REFLECTION—The angle between
the reflected wave and the normal.
ANGLE OF REFRACTION—The angle between
the normal and the path of a wave through the
second medium.
ANGSTROM UNIT—The unit used to define the
wavelength of light waves.
ANISOTROPIC—The property of a radiator to emit
strong radiation in one direction.
ANTENNA—A conductor or set of conductors used
either to radiate rf energy into space or to collect
rf energy from space.
APERTURE—See SLOT.
ARRAY OF ARRAYS—See COMBINATION
ARRAY.
BAY—Part of an antenna array.
BEARING—An angular measurement that indicates
the direction of an object in degrees from true
north. Also called azimuth.
BEVERAGE ANTENNA—A horizontal, longwire
antenna designed for reception and transmission
of low-frequency, vertically polarized ground
waves. Also known as WAVE ANTENNA.
BIDIRECTIONAL ARRAY—An array that radiates
in opposite directions along the line of maximum
radiation.
BROADSIDE ARRAY—An array in which the
direction of maximum radiation is perpendicular
to the plane containing the elements.
BOUNDARY CONDITIONS—The two conditions
that the E-field and H-field within a waveguide
must meet before energy will travel down the
waveguide. The E-field must be perpendicular
to the walls and the H-field must be in closed
loops, parallel to the walls, and perpendicular to
the E-field.
CAVITY RESONATOR—A space totally enclosed
by a metallic conductor and supplied with energy
in such a way that it becomes a source of
electromagnetic oscillations. The size and shape
of the enclosure determine the resonant frequency.
CENTER-FEED METHOD—Connecting the center
of an antenna to a transmission line, which is then
connected to the final (output) stage of the
transmitter. Also known as CURRENT-FEED
METHOD.
CHARACTERISTIC IMPEDANCE—The ratio of
voltage to current at any given point on a
transmission line. Represented by a value of
impedance.
CHOKE JOINT—A joint between two sections of
waveguide that provides a good electrical
connection without power losses or reflections.
AI-1
