Antenna radiation is made up of several different regions. Read on.
The transitions between these regions are not distinct and changes between them are gradual. The reactive near-field region is the region close to the antenna and up to about 1 wavelength away from any radiating surface. In the reactive region, the energy decays very rapidly with distance.
In the radiating near-field region, the average energy density remains fairly constant at different distances from the antenna, although there are localized energy fluctuations.
The radiating near-field region extends from the reactive region boundary out to a distance defined as, 2D2/l with D being the largest dimension of the antenna aperture, and l (lambda) being the wavelength.
Beyond this distance is the far-field region where the angular distribution of the energy does not vary with distance, and the power level decays according to the inverse square law with distance.