Helicoidal director for circularly polarised waves

A new type of director for circularly polarised waves is proposed and its characteristics investigated experimentally. The experiment is performed by using an Archimedean spiral antenna as a broadband exciter. It is revealed that the director composed of a helicoid operates over a frequency range of 1 to 2, which is broader than a conventional helix. It is also found that the gain relative to the spiral antenna shows a maximum value of about 5 dB when the axial length of the director is two wavelengths.