Circular polarization (Right-Hand Circular Polorization - RHCP and Left-Hand Circular Polorization - LHCP ) is primarily used in satellite communication.
In the trip through the various layers of the atmosphere/magnetosphere a typical horizontal or vertical polorized signal can/will change planes (and if you think about it, what's horizontal or vertical relative to an object in the sky?).
So, to negate / reduce the effect of the atmosphere, the signal is sent using a circular polorization. For a given antenna element count, a CP antenna will be about 3db less gain, but will tend to have less distortion and fading, compared to a similar antenna with linear polorization.
Uses are things like GPS and Direct Satellite broadcasting.
I don't think Cisco has any CP antennas. There is not much advantage to using them for terrestrial communications (at least not point-to-point / point-to-multipoint fixed-station comms).
Good Luck
Scott
