Everything about Circular Polarization totally explained
In
electrodynamics,
circular polarization (also
circular polarisation) 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 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
elliptical polarization. The other special case is the easier-to-understand
linear polarization.
Circular (and elliptical) 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 or
left, depending on the direction in which the electric field vector rotates. Unfortunately, two opposing historical conventions exist. In
physics,
astronomy, and
optics, polarization is defined as seen from the
receiver, such as a
telescope or
radio telescope. By this definition, if you could stop time and look at the electric field along the beam, it would trace a helix which is the same shape as the same-handed screw. For example, right circular polarization produces a right threaded (or forward threaded)
screw. In
electrical engineering, however, it's more common to define polarization as seen from the
source, such as from a transmitting antenna. In the U.S.,
Federal Standard 1037C also defines the handedness of circular polarization in this manner, or as looking in the direction of propagation. To avoid confusion, it's good practice to specify "as seen from the receiver" (or transmitter) when discussing polarization matters.
FM radio
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.
Circular dichroism
Circular dichroism (CD), is the differential absorption of left- and right-handed circularly polarized
light. It is a form of
spectroscopy used to determine the
optical isomerism and secondary structure of
molecules.
In general, this phenomenon will be exhibited in absorption bands of any
optically active molecule. As a consequence, circular dichroism is exhibited by biological molecules, because of the
dextrorotary (for example some
sugars) and
levorotary (for example some
amino acids) 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
The
classical sinusoidal plane wave solution of the
electromagnetic wave equation for the
electric and
magnetic fields is
» .
Further Information
Get more info on 'Circular Polarization'.
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