Editing Radio wave (section)

=== Polarization <span id="polarization_anchor" class="anchor"></span>===
Like other electromagnetic waves, a radio wave has a property called [[Polarization (waves)|polarization]], which is defined as the direction of the wave's oscillating [[electric field]] perpendicular to the direction of motion. A plane-polarized radio wave has an electric field that oscillates in a plane perpendicular to the direction of motion. In a [[horizontally polarized]] radio wave the electric field oscillates in a horizontal direction. In a [[vertical polarization|vertically polarized]] wave the electric field oscillates in a vertical direction. In a [[circularly polarized]] wave the electric field at any point rotates about the direction of travel, once per cycle. A [[right circular polarization|right circularly polarized]] wave rotates in a right-hand sense about the direction of travel, while a [[left circular polarization|left circularly polarized]] wave rotates in the opposite sense.<ref name="ITU">{{cite book |url=http://search.itu.int/history/HistoryDigitalCollectionDocLibrary/1.43.48.en.101.pdf |title=ITU Radio Regulations |publisher=[[International Telecommunication Union]] |year=2016 |isbn=9789261191214 |location=Geneva, CH |chapter=Ch. 1: Terminology and technical characteristics – Terms and definitions |archive-url=https://web.archive.org/web/20170829072058/http://search.itu.int/history/HistoryDigitalCollectionDocLibrary/1.43.48.en.101.pdf |archive-date=2017-08-29 |url-status=live}}</ref>{{rp|p.21}}  The wave's [[magnetic field]] is perpendicular to the electric field, and the electric and magnetic field are oriented in a [[right hand rule|right-hand sense]] with respect to the direction of radiation.

An antenna emits polarized radio waves, with the polarization determined by the direction of the metal antenna elements. For example, a [[dipole antenna]] consists of two collinear metal rods. If the rods are horizontal, it radiates horizontally polarized radio waves, while if the rods are vertical, it radiates vertically polarized waves. An antenna receiving the radio waves must have the same polarization as the transmitting antenna, or it will suffer a severe loss of reception. Many natural sources of radio waves, such as the sun, stars and [[blackbody radiation]] from warm objects, emit unpolarized waves, consisting of incoherent short wave trains in an equal mixture of polarization states.

The polarization of radio waves is determined by a [[quantum mechanical]] property of the [[photon]]s called their [[Spin (physics)|spin]]. A photon can have one of two possible values of spin; it can spin in a right-hand sense about its direction of motion, or in a left-hand sense. Right circularly polarized radio waves consist of photons spinning in a right hand sense. Left circularly polarized radio waves consist of photons spinning in a left hand sense. Plane polarized radio waves consist of photons in a [[quantum superposition]] of right and left hand spin states. The electric field consists of a superposition of right and left rotating fields, resulting in a plane oscillation.