An isotropic radiator is a transducer that produces useful electromagnetic field output in all directions with equal intensity, and at 100-percent efficiency, in three-dimensional space. If used for signal reception, the device is equally sensitive in all directions. In wireless communications and broadcasting, the isotropic radiator (also called an isotropic antenna ) is a theoretical ideal. It is sometimes referred to as a point source .
In wireless applications, an isotropic radiator can be approximated by constructing a single-turn square loop with a circumference of 1/2 wavelength , and then giving the loop a half-twist along an axis that lies in the plane of the loop.
The isotropic radiator is useful primarily as a standard laboratory reference source. The behavior and performance of more complex antennas is measured against it. A dipole antenna , for example, has signal output and sensitivity approximately 2.15 decibel s greater, in its favored directions, than the output and sensitivity of an isotropic antenna.