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Encyclopedia > Omnidirectional antenna

An omnidirectional antenna is an antenna system which radiates power uniformly in one plane with a directive pattern shape in a perpendicular plane. This pattern is often described as "donut shaped" A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ...


The only 3 dimensional omnidirectional antenna is the isotropic antenna, a theoretical construct derived from actual antenna radiation patterns and used as a reference for specifying antenna gain and radio system effective radiated power. Antenna gain (G) is defined as antenna efficiency (e) multiplied by antenna directivity (D) which is expressed mathematically as: G = eD. A useful relationship between omnidirectional radiation pattern directivity (D) in decibels and half-power beamwidth (HPBW) based on the assumption of a sinbθ / bθ pattern shape is:[1] An isotropic antenna is an ideal antenna that radiates power with unit gain uniformly in all directions and is often used to reference antenna gains in wireless systems. ... In telecommunication, the term radiation pattern has the following meanings: 1. ... In electronics, gain is usually taken as the mean ratio of the signal output of a system to the signal input of the system. ... In radio telecommunications, effective radiated power or ERP is determined by subtracting system losses from system gains. ... In electromagnetics, directivity is a property of the radiation pattern produced by an antenna. ... In electromagnetics, directivity is a property of the radiation pattern produced by an antenna. ... The decibel is a dimensionless unit (like percent) that is a measure of ratios on a logarithmic scale. ... In telecommunication, the term beamwidth has the following meanings: 1. ...



D = 10log_{10} {left ({101.5over {HPBW - 0.00272(HPBW)^2}}right )} ;; dB



Practical antennas approach omnidirectionality by providing uniform radiation or response only in one reference plane, usually the horizontal one parallel to the earth's surface.


Common low gain omnidirectional antennas are the whip antenna, a vertically orientated dipole antenna, the discone antenna, and the horizontal loop (or halo) antenna. A whip antenna is an antenna with a single driven element and a ground plane. ... A simple half-wave dipole antenna that a shortwave listener might build. ... A discone antenna is a version of a biconical antenna where one of the cones is replaced by a disc. ...


Higher gain omnidirectional antennas are the Coaxial Colinear (COCO) antenna[2] and Omnidirectional Microstrip Antenna (OMA)[3].


Omnidirectional antennas are generally realized using colinear dipole arrays. These arrays consist of half-wavelength dipoles with a phase shifting method between each element that ensures the current in each dipole is in phase[4]. The Coaxial Colinear or COCO antenna uses transposed coaxial sections to produce in-phase half-wavelength radiatiors. A Franklin Array uses short U-shaped half-wavelength sections whose radiation cancels in the far-field to bring each half-wavelength dipole section into equal phase.


References

  1. ^ McDonald, Noel, "Omnidirectional Pattern Directivity in the Presence of Minor Lobes: Revisited," IEEE Transactions on Antennas and Propagation Magazine, Volume 41, No. 2 April 1999, pp. 63-68
  2. ^ Judasz, T. and Balsley, B., "Improved Theoretical and Experimental Models for the Coaxial Colinear Antenna," IEEE Transactions on Antennas and Propagation, Vol. 37 No. 3, March 1989, pp. 289-296
  3. ^ Bancroft R, "Design Parameters of an Omnidirectional Planar Microstrip Antenna," Microwave and Optical Technology Letters, Vol 47. No. 5 December 5, 2005 pp. 414-418.
  4. ^ Johnson, R and Jasik, H Ed., "Antenna Engineering Handbook," McGraw Hill, 1984 page 27-14.

  Results from FactBites:
 
omnidirectional antenna - definition of omnidirectional antenna in Encyclopedia (116 words)
An omnidirectional antenna is an antenna system which radiates maximum power uniformly in all directions.
The perfectly omnidirectional antenna is the isotropic antenna, a theoretical construct derived from actual antenna radiation patterns and used as a reference for specifying antenna gain and radio system effective radiated power.
Practical antennas approach omnidirectionality by providing uniform radiation or response only in one reference plane, usually the horizontal one parallel to the earth's surface.
  More results at FactBites »

 
 

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