Far field
A far distance. It typically refers to the propagation of electromagnetic waves over long distances. Depending on the application, farfield may be contrasted with "nearfield" (short range) or with "midfield" (in between). A region in the free space at a much greater distance from a sound source than the linear dimensions of the source itself. It is also the region where the sound pressure decreases according to the inverse-square law: The sound pressure level decreases by 6 dB with each doubling of distance from the source.
Far-field E (electric) and B (magnetic) radiation field strengths decrease as the distance from the source increases, resulting in an inverse-square law for the power intensity of electromagnetic radiation in the transmitted signal. The far field is the region in which the field has settled into "normal" electromagnetic radiation. In this region, it is dominated by transverse electric or magnetic fields with electric dipole characteristics. In the far-field region of an antenna, radiated power decreases as the square of distance, and absorption of the radiation does not feed back to the transmitter.
In the far-field region, each of the electric and magnetic parts of the EM field is "produced by" (or associated with) a change in the other part, and the ratio of electric and magnetic field intensities is simply the wave impedance in the medium.
Antenna Fundamental (Antenna Basics). (2009). Retrieved from https://www.antenna-theory.com/basics/main.php
RP-Photonics Encyclopedia. (2022). Retrieved from https://www.rp-photonics.com/company.html