radiansphere

noun

A spherical region of radius λ/2π around a small dipole electromagnetic antenna. This is the distance at which the induction and radiation terms are equal in magnitude. Inside, the induction terms dominate. In radio antenna theory the radiansphere is a convenient definition for the boundary between near-field and far-field regions.

"The "radiansphere" is the boundary between the near field and the far field of a small antenna. Its radius is one radianlength (λ/2π), at which distance the three terms of the field are equal in magnitude. A "small" antenna is one somewhat smaller than the radiansphere, but it has a "sphere of influence" occupying the radiansphere.