User:Dave3457/Sandbox/Circular polarization

Left/Right Handedness Conventions
Circular polarization may be referred to as right handed or left handed, 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. Using this convention, left or right handedness is determined by pointing ones left or right thumb towards the source and matching the curling of ones fingers to the temporal rotation of the field as it passes a given point in space. When using this convention one can alternatively consider the sense of rotation of the field in space. If one freezes the wave in time, the handedness of the screw type nature of the field, matches the defined handedness of polarization.

When determining if the wave is clockwise or counter-clockwise circularly polarized, one again takes the point of view of the receiver and looking towards the source, one observes the direction of the temporal rotation of the field.

As a specific example, refer to the circularly polarized wave in the illustration. It is defined to be right-handed and the helix forms a right handed screw. Note that it is the nature of all screws and helices that it doesn't matter in which direction you point your thumb when determining its handedness. It is also considered clockwise circularly polarized because for a receiver observing the wave approaching, the field rotates in the clockwise direction as it passes a given point in space. This rotation is being referred to as its "temporal" rotation. This convention matches the U.S., [Federal Standard 1037C] convention.

In electrical engineering however, it is more common to define polarization as seen from the source, such as from a transmitting antenna. When using this convention, left or right handedness is determined by pointing ones left or right thumb away from the source and matching the curling of ones fingers to the temporal rotation of the field. In this case the handedness of the helix does not match the defined handedness of the wave. When determining if the wave is clockwise or counter-clockwise circularly polarized, one takes the point of view of the transmitter, and while looking in the same direction which the wave is propagating, observes the direction of the temporal rotation of the field. This convention is in conformity with the [IEEE] standard.

To avoid confusion, it is good practice to specify "as seen from the receiver" (or transmitter) when discussing polarization matters. In each instance the thumb points away from the viewer.