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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: =.
Isotropic antennas, which don't actually exist, should not be confused with omnidirectional antennas, which are real and fairly common. An isotropic antenna radiates equal power in all three dimensions, while an omnidirectional antenna radiates equal power in all horizontal directions, but little or none
These axially symmetric antennas have radiation patterns with a similar symmetry, called omnidirectional patterns; they radiate equal power in all directions perpendicular to the antenna, with the power varying only with the angle to the axis, dropping off to zero on the antenna's axis. This illustrates the general principle that if the shape ...
A halo antenna is a self-resonant antenna: Its feedpoint impedance is reactance-free / purely resistive at the design frequency. A small loop antenna, on the other hand, has lower radiation resistance [ b ] and is not self-resonant; it requires some form of impedance matching to counter the loop's reactance – in practice, this usually ...
An automobile's whip antenna, a common example of an omnidirectional antenna. Antennas can be classified as omnidirectional, radiating energy approximately equally in all horizontal directions, or directional, where radio waves are concentrated in some direction(s).
The whip antenna is a monopole antenna, and like a vertical dipole has an omnidirectional radiation pattern, radiating equal radio power in all azimuthal directions (perpendicular to the antenna's axis), with the radiated power falling off with elevation angle to zero on the antenna's axis. [1]
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.
Omnidirectional refers to the notion of existing in every direction. Omnidirectional devices include: Omnidirectional antenna, an antenna that radiates equally in all directions; VHF omnidirectional range, a type of radio navigation system for aircraft; Omnidirectional camera, a camera that can see all 360 degrees around it
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