Far-field region

In telecommunication, far-field region is the region where the angular field distribution is essentially independent of distance from the source.

Note 1: If the source has a maximum overall dimension D that is large compared to the wavelength, the far-field region is commonly taken to exist at distances greater than 2D ²/λ from the source, λ being the wavelength.

Note 2: For a beam focused at infinity, the far-field region is sometimes referred to as the Fraunhofer region. Synonyms far field, far zone, Fraunhofer region, radiation field.

Source: from Federal Standard 1037C and from MIL-STD-188