How does this UHF antenna works?
This is a circularly polarized antenna. The central disc is fed at two points at 90&deg; from each other; furthermore, these two feed points have different lengths of transmission line from the connector. You'll find that the difference in lengths corresponds to a 90&deg; phase shift at the operating frequency.

Two fields at 90&deg; to each other, fed with a phase shift of 90&deg;, combine to create a radio wave whose polarization rotates at it propagates away from the face of the disc. This is called circular polarization.