Isotropic radiator

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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.

1 Physics
2 See also
3 External links

[edit] 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]

[edit] 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

$E\left(r,\theta,\phi\right)=\frac{e^{jkr}}{4\pi r}$ (note that this function is independent of the spherical angles $\displaystyle\theta$ and $\displaystyle\phi$ )

would violate the Helmholtz Wave Equation, as derived from Maxwell's Equations.

Although the Sun radiates equally in all directions, its radiation pattern does not violate Maxwell's equations, because the Sun's radiation is incoherent.

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.

[edit] 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.