Fraunhofer distance

The Fraunhofer distance, named after Joseph von Fraunhofer, is the value of:

${\displaystyle d={{2D^{2}} \over {\lambda }},}$

where D is the largest dimension of the radiator (in the case of a magnetic loop antenna, the diameter) and ${\displaystyle {\lambda }}$ is the wavelength of the radio wave. This distance provides the limit between the near and far field, allowing for 22.5 degrees of phase deviation over the face of the radiator.