Phase center
The term phase center describes the electronic reference point of an antenna . Viewed from the receiving point, the electromagnetic antenna radiation seems to emanate from this point.
example
The phase center of an antenna plays a major role in measurement processes by determining the transit time.
A global navigation satellite system measures the location with an accuracy of a few meters. The error is significantly larger than the wavelength and antenna dimensions; the exact position of the phase center is irrelevant. In contrast, with DGPS , the position can be determined with a few millimeters accuracy, relative to the phase center. The position of the phase center in the antenna depends on both the wavelength and the angle of incidence. The current position of the phase center is indicated relative to an antenna reference point (ARP) on the antenna.