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. Note 2: 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. Note 1: Examples of absolute gain are no-load gain, full-load gain, and small-signal gain. Note 2: Absolute gain is usually expressed in dB.

Absorption: In the transmission of electrical, electromagnetic, or acoustic signals, the conversion of the transmitted energy into another form, usually thermal. Note 1: Absorption is one cause of signal attenuation. Note 2: The conversion takes place as a result of interaction between the incident energy and the material medium, at the molecular or atomic level.

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.

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

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: Current that is continually changing in magnitude and periodically in direction from a zero reference level. Also called AC.

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. 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: 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. Also called AM.

Angle of incidence: The acute angle (smaller angle) at which a wave of energy strikes an object or penetrates a layer of the atmosphere or ionosphere.

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