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In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to the direction of the wave.
Circular polarization is commonly used to reduce the effect of atmospheric depolarization on the communication system performance. [17] A dual-band reflectarray has two different passband frequencies, for example for uplink and downlink . [ 18 ]
Most antennas are nominally linearly polarized, but elliptical and circular polarization is a possibility. In the case of linear polarization, the same kind of filtering as described above, is possible.
Note that for circular polarization, optical researchers use the opposite right-hand rule [citation needed] from the one used by radio engineers. It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception.
This antenna is unusual in that it radiates in all directions (no nulls in the radiation or reception pattern), with horizontal polarization in directions coplanar with the elements, circular polarization normal to that plane, and elliptical polarization in other directions. Used for receiving signals from satellites, as circular polarization ...
Polarization diversity combines pairs of antennas with orthogonal polarizations (i.e. horizontal/vertical, ± slant 45°, Left-hand/Right-hand circular polarization etc.). Reflected signals can undergo polarization changes depending on the medium through which they are traveling.
Vivaldi antennas can be made for linear polarized waves or – using two devices arranged in orthogonal direction – for transmitting / receiving both polarization orientations. If fed with 90° phase-shifted signals, orthogonal devices can transmit/receive circular -oriented electromagnetic waves .
Circular polarization was used for spacecraft (satellite and missile) communication, since circular polarization is not sensitive to the relative orientation of the antennas, and the space vehicle's antenna could have any orientation with respect to the ground antenna. High gain Yagi turnstile antennas were often used for the ground station.