A zone extending from infinity to near an antenna within which the radiation from the antenna can be considered to be travelling directly away from the antenna; the electric and magnetic field components are then transverse to the direction from the antenna to that point (see electromagnetic radiation). For an antenna of size D the far-field region begins at a distance of approximately 2D2/λ from the antenna for radiation of wavelength λ. In this region, the power density from the antenna falls off as the inverse square of the distance from the antenna while the fields fall off as the inverse of this distance.
The near-field region of an antenna is a zone extending from the antenna out to the far-field region. Within the near-field region, the fields generated by the antenna may be oriented in any direction and decrease rapidly, up to the inverse square of the distance from the antenna.