A three-dimensional section of the radiation pattern of a directional antenna, bounded by one or more cones of nulls or by regions of diminished irradiance.

The process of adjusting impedance so that the input impedance of an antenna equals or approximates the characteristic impedance of its transmission line over a specified range of frequencies.
Note: The impedance of either the transmission line, or the antenna, or both, may be adjusted to effect the match.

The temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output noise power per unit bandwidth as that at the antenna output at a specified frequency.
Note 1: The antenna noise temperature depends on antenna coupling to all noise sources in its environment as well as on noise generated within the… (Read More →)

Synonym left-hand polarized wave.

Pertaining to equipment, processes, or techniques used to reduce the effect of natural and man-made noise on radio communications.

Measures ensuring that intended transmitted information can be received despite deliberate jamming attempts. [INFOSEC-99]

A point in a standing wave at which the amplitude is a maximum.

1. Measures taken to prevent an unauthorized person/entity from impersonating an authorized person/entity to gain access to a data system. [DoJ]
2. Measures preventing an opponent's participation in an information system (IS). [INFOSEC-99]

A computer program designed to detect computer-file viruses and possibly to suggest or take corrective action. Synonym vaccine program. [After 2382-pt.8]

A thin, dielectric or metallic film, or several such films, applied to an optical surface to reduce its reflectance and thereby increase its transmittance. [After 2196]
Note: For minimum reflection of a normal incident wave of a single wavelength, the antireflection coating may consist of a single layer and must have (a) a refractive index equal to the square root… (Read More →)