Phase Centre

The radiation phase centre of an antenna is the point from where the structure seems to radiate a spherical wave. For an isotropic radiator, the phase centre would be the point where the isotropic radiator is located.

For general radiated fields, a single-phase centre location does not exist since antennas are not isotropic radiators. True isotropic radiators do not exist, but a radiation pattern can approximate an isotropic radiator over a limited angular range. The implication is that the position the phase centre depends on the observation point and thus from each view direction, the radiation source seems to be located at a different location. For a section of a radiation pattern (usually a section of the main beam) a “nominal” phase centre can usually be found and is of practical use to antenna designers.

The phase centre calculation is often used during the design of reflector antennas. Place the antenna such that the phase centre of the antenna is at the focal point of the reflector.