In electrodynamics, circular polarization of electromagnetic radiation is a polarization such that the tip of the electric field vector, at a fixed point in space, describes a circle as time progresses. The name is derived from this fact. The electric vector, at one point in time, describes a helix along the direction of wave propagation (see the polarization article for pictures). The magnitude of the electric field vector is constant as it rotates. Circular polarization is a limiting case of the more general condition of eliptical polarization. The other special case is the easier to understand linear polarization.
Circular (and eliptical) polarization is possible because the propagating electric (and magnetic) fields can have two orthogonal components with independent amplitudes and phases (and the same frequency).
A circularly polarized wave may be resolved into two linearly polarized waves, of equal amplitude, in phase quadrature (90 degrees apart) and with their planes of polarization at right angles to each other.
Circular polarization may be referred to as "right-hand" or "left-hand," depending on the direction in which the electric field vector rotates. When looking toward the source, right hand circular polarized light rotates clockwise as time increases, and describes a right hand helix along the propagation axis.
The term "Circular Polarisation" 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 polarisation.
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