Antenna terms, and definitions

Absolute gain: Of an antenna, for a given direction and polarization, the ratio of (a) the power that would be required at the input of an ideal isotropic radiator to (b) the power actually supplied to the given antenna, to produce the same radiation intensity in the far-field region. Note 1: If no direction is given, the absolute gain of an antenna corresponds to the direction of maximum effective radiated power. Absolute gain is usually expressed in dB. Synonym isotropic gain. Of a device, the ratio of (a) the signal level at the output of the device to (b) that of its input under a specified set of operating conditions. Examples of absolute gain are no-load gain, full-load gain, and small-signal gain.

Absorption: In the transmission of electrical, electromagnetic, or acoustic signals, the conversion of the transmitted energy into another form, usually thermal. Absorption is one cause of signal attenuation.

Absorption loss: That part of the transmission loss caused by the dissipation or conversion of electrical, electromagnetic, or acoustic energy into other forms of energy as a result of its interaction with a material medium.

Acceptance pattern: Of an antenna, for a given plane, a distribution plot of the off-axis power relative to the on-axis power as a function of angle or position. Note: The acceptance pattern is the equivalent of a horizontal or vertical antenna pattern. Of an optical fiber or fiber bundle, a curve of total transmitted power plotted against the launch angle.

Active Antenna: An antenna that has an active element or one that uses active components.

Active Element: The element, of a multielement antenna, that is actually being driven by an RF signal.

Actual Ground: The ground plane as seen by an antenna. Ground as determined by an antenna my be the physical ground [earth] or an artificial ground plane made from a conductive material [see Ground Screen].

Adcock Antenna: An antenna array consisting of four equidistant vertical elements which can be used to transmit or receive directional radio waves. An out-dated type of antenna.

Aerial: An antenna. The part of a radio system that radiates energy into space.

Aerial Array: An arrangement of any number of elements for radiating or receiving signals in a directional manner. Also see Antenna Array, and Beam Antenna.

Aerial cable: A communications cable designed for installation on, or suspension from, a pole or other overhead structure.

Aerodiscone Antenna: See Discone Antenna. A [seldom used] term used describe a miniature discone antenna designed for use on aircraft [Aeronautics].

Alexander Antenna. A VHF antenna.

Alford Antenna. A square loop antenna. Related term Alford Slot Antenna.

All-Wave Antenna. An old term used to describe an antenna that operates over a wide frequency range.

Altazimuth mount: A mounting, for a directional antenna or telescope, in which slewing takes place in (a) the plane tangent to the surface of the Earth or other frame of reference and (b) elevation about, i.e., above or below, that plane. Synonym x-y mount. {alt-azimuth mount}.

Alternating current: [AC] Current that is continually changing in magnitude and periodically in direction from a zero reference level.

AM Broadcast Range: Includes the frequencies between 540 to 1600 kHz with AM channels spaced at 10kHz intervals.

Amplification: The process of increasing the strength (current, voltage, or power) of a signal.

Amplifier: An electronic component that boosts the voltage or power level of a signal that is a linear replica of the input signal, but with greater power or voltage level, and sometimes with an impedance transformation. The output may also be a nonlinear analog function of the input signal, as in a signal compression device. Also See fiber amplifier, optical repeater. Reference Amplifier Manufacturers.

Amplitude: The level of an audio or other signal in voltage or current. The magnitude of variation in a changing quantity from its zero value.

Amplitude Modulation: [AM] Modulation in which the amplitude of the carrier wave is varied above and below its normal value in accordance with the intelligence of the signal being transmitted.

Editor Comment; this dictionary uses the term Antenna when required to define a term, and does not use the term Aerial. Although the term Aerial is defined here, it is only defined to show that it means the same thing as an Antenna. The word Aerial is synonyms with Antenna. This antenna dictionary also purposely covers or defines out dated names for antennas while the main engineering dictionary drops obsolete terms that are no longer used.