Circular polarization: Difference between revisions

Revision as of 13:01, 22 November 2024

Revision as of 07:50, 27 December 2024

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In a circularly polarized electromagnetic wave, the individual electric field vectors, as well as their combined vector, have a constant [[Magnitude (vector)|magnitude]], and with changing phase angle. Given that this is a [[plane wave]], each vector represents the magnitude and direction of the electric field for an entire plane that is perpendicular to the optical axis. Specifically, given that this is a [[Plane wave#Polarized electromagnetic plane waves|circularly polarized plane wave]], these vectors indicate that the electric field, from plane to plane, has a constant strength while its direction steadily rotates. Refer to [[Plane wave#Polarized electromagnetic plane waves|these two images]]{{dead link|date=January 2021}} in the plane wave article to better appreciate this dynamic. This light is considered to be right-hand, clockwise circularly polarized if viewed by the receiver. Since this is an [[Electromagnetic radiation|electromagnetic wave]], each [[electric field]] vector has a corresponding, but not illustrated, [[magnetic field]] vector that is at a [[right angle]] to the electric field vector and [[Proportionality (mathematics)|proportional]] in magnitude to it. As a result, the magnetic field vectors would trace out a second helix if displayed.

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== FM radio ==

[[File:KHTB-FM broadcasting antennas LakeMountain.jpg|thumb|upright=0.6|Crossed-dipole antenna array of station [[KENZ (FM)|KENZ]]'s {{nowrap|94.9 MHz}}, {{nowrap|48 kW}} transmitter on Lake Mountain, Utah. It radiates [[circular polarization|circularly polarized]] radio waves.]]

[[FM broadcasting|FM broadcast]] radio stations sometimes employ circular polarization to improve signal penetration into buildings and vehicles. It is one example of what the [[International Telecommunication Union]] refers to as "mixed polarization", i.e. radio emissions that include both horizontally- and vertically-polarized components.<ref>{{cite report |title=Report 464-5, "Polarization of Emissions in Frequency-Modulation Broadcasting in Band 8 (VHF)" |year=1990 |url=https://www.itu.int/dms_pub/itu-r/opb/rep/r-rep-bs.464-5-1990-pdf-e.pdf |publisher=International Telecommunications Union}}</ref> In the United States, [[Federal Communications Commission]] regulations state that horizontal polarization is the standard for FM broadcasting, but that "circular or elliptical polarization may be employed if desired".<ref>{{CodeFedReg |47|73|316}}</ref>