Cycloid dipole antenna

Image of the Cycloid dipole antenna.

The Cycloid dipole, also known as the 'Ring and Stub', is an omnidirectional, circularly polarised antenna used primarily in FM broadcasting applications. As the physical structure of the Cycloid dipole is not symmetrical, it is typically side-mounted on masts or towers and multiple elements may be stacked to realize vertical arrays and increase gain.

Polarisation-specific radiation patterns for a right hand circular (RHC) design.

The near-horizontal loop section provides a horizontal component for the radiation, while the vertical sections provide a vertical component. If the dimensions of the loop and vertical elements are chosen correctly, the amount of vertical and horizontal radiation, together with the correct delay between these components, will result in circular polarisation. Typically the Cycloid dipole is matched to 50 Ohm and has a narrow impedance bandwidth.

The cycloid dipole has a very narrow impedance bandwidth.