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Circular polarization is a limiting case of elliptical polarization. The other special case is the easier-to-understand linear polarization . All three terms were coined by Augustin-Jean Fresnel , in a memoir read to the French Academy of Sciences on 9 December 1822.
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.
An antenna's polarization can sometimes be inferred directly from its geometry. When the antenna's conductors viewed from a reference location appear along one line, then the antenna's polarization will be linear in that very direction. In the more general case, the antenna's polarization must be determined through analysis.
Turnstile antennas can be stacked and fed in phase to realize an omnidirectional broadside array or phased for an end-fire array with circular polarization. The batwing antenna is a turnstile antenna with its linear elements widened as in a bow-tie antenna, again for the purpose of widening its resonant frequency and thus usable over a larger ...
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 ...
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 .
The receiving feed antenna must also have vertical polarization to receive them; if the feed is horizontal (horizontal polarization) the antenna will suffer a severe loss of gain. To increase the data rate, some parabolic antennas transmit two separate radio channels on the same frequency with orthogonal polarizations, using separate feed ...
Unlike a dipole antenna, the polarization of a resonant loop antenna is not obvious from the orientation of the loop itself, but depends on the placement of its feedpoint. [e] If a vertically oriented loop is fed at the bottom, then its radiation will be horizontally polarized; feeding it from the side will make it vertically polarized.