An electromagnetic wave or signal traveling from “here” to “there” has an electrostatic field component that we call its E-field and whose direction we assign as the signal’s polarity. Often, the E-field is either vertical or horizontal as developed by a dipole structure or a ground plane antenna, but it can also be rotary which means it can be rotating around the signal’s axis of travel. The conventional terminology for that case however is not the word “rotary”, it is the word “circular”. We thus speak of vertical polarization, horizontal polarization, and circular polarization.
What grammarian made that decision is anyone’s guess, but that’s how things are.
It isn’t hard to create a circularly polarized signal. Please see Figure 1.
Figure 1 Making a circularly polarized signal is achieved by feeding both polarizations at the same time but with a 90o signal phase shift between the two.
A circularly polarized signal has a handedness which is defined from the point of view of the signal’s recipient. If the E-field is rotating clockwise from the recipient’s observation point, the signal is right hand polarized (RHP). If the E-field is rotating counterclockwise from the recipient’s observation point, the signal is left hand polarized (LHP). When I was at Sirius Satellite Radio prior to the merger with XM Radio, I learned that their Sirius satellite signals were LHP.
If you the recipient of an incoming signal point your right-hand thumb along the axis of signal arrival, your remaining four fingers will curl to your right for RHP, the direction of E-field rotation. If you the recipient of an incoming signal point your left-hand thumb along the axis of signal arrival, your remaining four fingers will curl to your left for LHP, the direction of E-field rotation.
Got that?
One advantage of circular polarization is a reduced susceptibility to signal fading over long distances. Various factors can affect the polarization of the traveling signal, and the degree of fading can be different between different degrees of polarization angle. Vertical and horizontal polarizations share this vulnerability.
Circular polarization is less susceptible to signal fading since the polarization most easily propagated is achieved whatever the intervening propagation environment might happen to be. In ham radio, this is a noted advantage of “cubical quad” antennas over multi-element Yagi antennas. Cubical quads deliver circular polarization.
Please see this article.
Where “QSB” stands for signal fading and “DX” stands for long distance communication, we find the following:
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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