Editing Near and far field (section)

{{Short description|Regions of an electromagnetic field}}
{{About|the electromagnetic concept|the mathematical|Near-field (mathematics)}}
{{Redirect|Far field}}
[[File:FarNearFields-USP-4998112-1.svg|thumb|265px|Order of the [[Fraunhofer diffraction]] (inner, ''reactive near field'') and [[Fresnel diffraction]] (outer, ''radiative near field'') regions, relative to the ''far field''.]]
{{Antennas|sources/regions}}

The '''near field''' and '''far field''' are regions of the [[electromagnetic field|electromagnetic (EM) field]] around an object, such as a transmitting [[antenna (radio)|antenna]], or the result of radiation scattering off an object. Non-radiative ''near-field'' behaviors dominate close to the antenna or scatterer, while [[electromagnetic radiation]] ''far-field'' behaviors predominate at greater distances.

'''Far-field''' {{math|'''E'''}} (electric) and {{math|'''B'''}} (magnetic) radiation field strengths decrease as the distance from the source increases, resulting in an [[inverse-square law]] for the ''[[power (physics)|power]]'' intensity of [[electromagnetic radiation]] in the transmitted signal. By contrast, the '''near-field'''{{'}}s {{math|'''E'''}} and {{math|'''B'''}} strengths decrease more rapidly with distance: The radiative field decreases by the [[inverse-square law|inverse-distance squared]], the reactive field by an inverse-''cube'' law, resulting in a diminished power in the parts of the electric field by an inverse fourth-power and sixth-power, respectively. The rapid drop in power contained in the near-field ensures that effects due to the near-field essentially vanish a few wavelengths away from the radiating part of the antenna, and conversely ensure that at distances a small fraction of a wavelength from the antenna, the near-field effects overwhelm the radiating far-field.