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Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: =.
Although dipoles are used alone as omnidirectional antennas, they are also a building block of many other more complicated directional antennas. Half-wave dipole The most common type of dipole consists of two resonant elements, each just under a quarter wavelength long, hence a total length of about a half-wave.
Antenna arrays may employ any basic (omnidirectional or weakly directional) antenna type, such as dipole, loop or slot antennas. These elements are often identical. Log-periodic and frequency-independent antennas employ self-similarity in order to be operational over a wide range of bandwidths .
Omnidirectional antennas used by a number of stations radiate the signal equally in all horizontal directions. Directional arrays are used to protect co- or adjacent channel stations, usually at night, but some run directionally continuously.
Patch antenna gain pattern. A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only.
This is a high gain omnidirectional antenna, often used in the VHF band as broadcasting antennas for television stations and base station antennas for land mobile two-way radios. Superturnstile or Batwing array – specialized vertical antenna used for television broadcasting consisting of multiple crossed-dipole antennas mounted collinearly on ...
The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
LOFAR consists of a vast array of omnidirectional radio antennas using a modern concept, in which the signals from the separate antennas are not connected directly electrically to act as a single large antenna, as they are in most array antennas. Instead, the LOFAR dipole antennas (of two types) are distributed in stations, within which the ...