Fraunhofer distance

The Fraunhofer distance, named after Joseph von Fraunhofer, is the value of:
 * $$d = {{2D^2}\over{\lambda}},$$

where D is the largest dimension of the radiator (in the case of a magnetic loop antenna, the diameter) and $${\lambda}$$ 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.