page_title: Near and far field
section_title: Regions according to diffraction behavior
hierarchical_section_title: Near and far field / Definitions / Regions according to diffraction behavior
context_page_description: The near field and far field are regions of the electromagnetic field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative 'near-field' behaviors dominate close to the antenna or scattering object, while electromagnetic radiation 'far-field' behaviors dominate at greater distances.
  Far-field E and B field strength decreases as the distance from the source increases, resulting in an inverse-square law for the radiated power intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance: the radiative field decreases by the inverse-distance squared, the reactive field by an inverse cubed 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.
caption: Near- and far-field regions for an antenna larger (diameter or length D) than the wavelength of the radiation it emits, so that ​D⁄λ  ≫ 1 . Examples are radar dishes, satellite dish antennas, radio telescopes, and other highly directional antennas.