Information about Isotropic Antenna
An isotropic radiator is a theoretical point source of waves which exhibits the same magnitude or properties when measured in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centred on the source. It is a reference radiator with which other sources are compared. Isotropic radiators obey Lambert's law.
In reality, a coherent isotropic radiator cannot exist, as the isotropic radiator, with a radiation pattern (as expressed in spherical coordinates) of
Although the Sun and other stars radiate equally in all directions, their radiation pattern does not violate Maxwell's equations, because radiation from a star is incoherent. Sound waves also expand uniformly in all directions, but sound waves are longitudinal waves and not transverse waves.
Even though an isotropic radiator cannot exist in practice, antenna directivity is usually compared to the directivity of an isotropic radiator, because the gain (which is closely related to directivity) relative to an isotropic radiator is useful in the Friis transmission equation. The smallest directivity a radiator can have relative to an isotropic radiator, is a Hertzian Dipole, which has 1.76 dBi.
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Physics
A point radiation or sound source. At a distance, the sun is an isotropic radiator of electromagnetic radiation. The Big Bang is another example of an isotropic radiator - the Cosmic Microwave Background. [1]Antenna Theory
In antenna theory, the isotropic radiator is a theoretical radiator having a directivity of 0 dBi (dB relative to isotropic), which means that the radiator equally transmits (or receives) electromagnetic radiation from any arbitrary direction.In reality, a coherent isotropic radiator cannot exist, as the isotropic radiator, with a radiation pattern (as expressed in spherical coordinates) of
- (note that the magnitude of this function is independent of the spherical angles
and 
, but it is permissible for the vector's direction, as represented by the unit vector 
to be a function of and )
Although the Sun and other stars radiate equally in all directions, their radiation pattern does not violate Maxwell's equations, because radiation from a star is incoherent. Sound waves also expand uniformly in all directions, but sound waves are longitudinal waves and not transverse waves.
Even though an isotropic radiator cannot exist in practice, antenna directivity is usually compared to the directivity of an isotropic radiator, because the gain (which is closely related to directivity) relative to an isotropic radiator is useful in the Friis transmission equation. The smallest directivity a radiator can have relative to an isotropic radiator, is a Hertzian Dipole, which has 1.76 dBi.
Hairy ball theorem
Another way to explain why an isotropic radiator cannot exist is by using the hairy ball theorem, which asserts that a continuous vector field tangent to the surface of the sphere, must fall to zero at at least one point on the sphere. This means that there some direction for which the electric field must be zero, and hence, non-uniform.Optics
A point source of light. The sun approximates an isotropic radiator of light. Certain munitions such as flares and chaff have isotropic radiator properties.Sound
An isotropic radiator is a theoretical perfect speaker exhibiting equal sound volume in all directions.See also
References
External links
- Isotropic Radiators, Matzner and McDonald, arXiv Antennas
- isotropic radiator Whatis.com
- Antennas D.Jefferies
- isotropic radiator AMS Glossary
- U.S. Patent 4,130,023 - Method and apparatus for testing and evaluating loudspeaker performance
- Non Lethal Concepts - Implications for Air Force Intelligence Published Aerospace Power Journal, Winter 1994
- [https://ewhdbks.mugu.navy.mil/Glossary.htm Glossary]
- Cosmic Microwave Background - Introduction
A point source is a single identifiable localized source of something. A point source has negligible extent, distinguishing it from other source geometries. Sources are called point sources because in mathematical modeling, these sources can usually be approximated as a
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Lambert's cosine law in optics says that the radiant intensity observed from a "Lambertian" surface is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal.
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Big Bang is the cosmological model of the universe whose primary assertion is that the universe has expanded into its current state from a primordial condition of enormous density and temperature.
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cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred to as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe [1].
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In electromagnetics, directivity is a figure of merit for an antenna. It measures the power density an actual antenna radiates in the direction of its strongest emission, relative to the power density radiated by an ideal isotropic radiator antenna radiating the same amount of
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Coherence is the property of wave-like states that enables them to exhibit interference. It is also the parameter that quantifies the quality of the interference (also known as the degree of coherence).
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radiation pattern most commonly refers to the directional (angular) dependence of radiation from the antenna or other source (synonyms: antenna pattern, far-field pattern).
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spherical coordinate system is a coordinate system for representing geometric figures in three dimensions using three coordinates: the radial distance of a point from a fixed origin, the zenith angle from the positive z-axis, and the azimuth angle from the positive x-axis.
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Helmholtz equation, named for Hermann von Helmholtz, is the elliptic partial differential equation
where is the Laplacian, is a constant, and the unknown function is defined on n-dimensional Euclidean space Rn
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where is the Laplacian, is a constant, and the unknown function is defined on n-dimensional Euclidean space Rn
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For thermodynamic relations, see .
In electromagnetism, Maxwell's equations are a set of four equations that were first presented as a distinct group in 1884 by Oliver Heaviside in conjunction with Willard Gibbs...... Click the link for more information.
The Sun
Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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Observation data
Mean distance
from Earth 1.4961011 m
(8.31 min at light speed)
Visual brightness (V) −26.74m [1]
Absolute magnitude 4.
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STAR is an acronym for:
Organizations:
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Organizations:
- Society for Telescopy, Astronomy, and Radio, a non-profit astronomy club in New Jersey
- Special Tasks and Rescue or Special Tactics and Response, synonyms for SWAT
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Coherence is the property of wave-like states that enables them to exhibit interference. It is also the parameter that quantifies the quality of the interference (also known as the degree of coherence).
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Longitudinal waves are waves that have vibrations along or parallel to their direction of travel. They include waves in which the motion of the medium is in the same direction as the motion of the wave.
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transverse wave is a wave that causes vibration in the medium in a perpendicular direction to its own motion. For example: if a wave moves along the x-axis, its disturbances are in the yz-plane.
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The Friis transmission equation is used in telecommunications engineering, and gives the power transmitted from one antenna to another under idealized conditions. (It is not to be confused with the Friis' formula used to compute noise figure, which is discussed in a separate
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hairy ball theorem of algebraic topology states that there is no nonvanishing continuous tangent vector field on the sphere. If f is a continuous function that assigns a vector in R3 to every point p on a sphere such that f(p
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In mathematics, a continuous function is a function for which, intuitively, small changes in the input result in small changes in the output. Otherwise, a function is said to be discontinuous.
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vector field is a construction in vector calculus which associates a vector to every point in a (locally) Euclidean space.
Vector fields are often used in physics to model, for example, the speed and direction of a moving fluid throughout space, or the strength and direction
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Vector fields are often used in physics to model, for example, the speed and direction of a moving fluid throughout space, or the strength and direction
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tangent has two distinct but etymologically-related meanings: one in geometry and one in trigonometry.
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Geometry
In plane geometry, a line is tangent to a curve, at some point, if both line and curve pass through the point with the oppsite direction...... Click the link for more information.
radiation pattern most commonly refers to the directional (angular) dependence of radiation from the antenna or other source (synonyms: antenna pattern, far-field pattern).
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The E-plane and H-plane are reference planes for linearly polarized antennas.
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E-Plane
For a linearly polarized antenna, this is the plane containing the electric field vector and the direction of maximum radiation...... Click the link for more information.
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