farfield
Farfield, or the Fraunhofer region, is the region of a radiated wave field where wavefronts are effectively planar and the angular distribution of radiation is essentially distance‑independent. In the far field the field amplitude decreases roughly as 1/r and the phase varies linearly with distance. The concept applies across electromagnetism, acoustics, and optics for sources such as antennas, loudspeakers, and optical apertures.
Boundaries between near and far field depend on wavelength λ and the source size D (largest dimension).
In the far field, the electric and magnetic fields are transverse to the propagation direction and related
Applications include antenna and radar design, wireless and optical communications, and acoustic testing. The far-field approximation