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The term "circular polarization" is often used erroneously to describe mixed polarity signals used mostly in [[FM radio]] (87.5 to 108.0 MHz), where a vertical and a horizontal component are propagated simultaneously by a single or a combined array.
This has the effect of producing greater penetration into buildings and difficult reception areas than a signal with just one plane of polarization.
:''Main article: [[Circular dichroism]]''
'''Circular dichroism (CD)''', is the differential absorption of left- and right-handed [[circular polarization|circularly polarized]] [[light]]. It is a form of [[spectroscopy]] used to determine the [[optical isomerism]] and secondary structure of [[molecule]]s.
In general, this phenomenon will be exhibited in absorption bands of any [[optical activity|optically active]] molecule. As a consequence, circular dichroism is exhibited by biological molecules, because of the [[dextrorotary]] (e.g. some [[sugar]]s) and [[levorotary]] (e.g. some [[amino acid]]s) molecules they contain. Noteworthy as well is that a [[secondary structure]] will also impart a distinct CD to its respective molecules. Therefore, the [[alpha helix]] of proteins and the [[double helix]] of [[nucleic acids]] have CD spectral signatures representative of their structures.
==Mathematical description of circular polarization==
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*[[Elliptical polarization]]
*[[photon polarization]]
▲*[[Circular dichroism]]
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