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 longdistance 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.
APERTURE—See SLOT.
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.
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.
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