An isotropic radiator is a hypothetical radiator (for example, an antenna) that radiates uniformly in all directions. The radiation pattern of an isotrope is a sphere; in other words, the gain of such a radiator is the same in all directions.
The isotropic radiator is used to compare the power flux radiated by a real antenna, according to its radiation pattern, with the uniformly radiated power of an isotropic radiator in all directions. In antenna engineering, the isotropic radiator is taken as a reference for comparing the directional properties of different antennas, in particular when determining their directivity factor. The gain of an isotropic antenna is taken as 0 dBi, i.e., the reference point.
An isotropic radiator, which radiates the electric and magnetic components of an electromagnetic wave equally effectively, cannot be physically realized. In antenna engineering, for research purposes, either an electric or, depending on the study’s goal, a magnetic elementary radiator is used. An electric elementary radiator is physically a dipole whose length is many times (hundreds of times) smaller than the wavelength. A magnetic elementary radiator is a loop whose perimeter is also many times (hundreds of times) smaller than the wavelength.
Much attention is given to developing antennas whose directional properties are close to those of an isotropic radiator. They are particularly necessary for use on artificial Earth satellites that are not stabilized in space. Such antennas ensure stable communication with the satellite regardless of its orientation in space.