RHCP Helix Antenna

Right-Handed (clockwise ) Circularly Polarized Helix antenna

A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one of two principal modes: normal (broadside) mode or axial (or endfire) mode. RHCP helix antenna operate in axial mode.

The helix dimensions are at or above the wavelength of operation. The antenna then falls under the class of waveguide antennas, and produces true circular polarization. The orientation of the sender and receiver cannot be easily controlled, or where the polarization of the signal may change. Antenna size makes them unwieldy for low frequency operation, so they are commonly employed only at frequencies ranging from VHF up to microwave. Helical antennas can receive signals with any type of linear polarization, such as horizontal or vertical polarization.

Helical antennas are composed of a single driven element S which is coiled in a helix. The winding sense of the coil determines its polarization, while the space between the coils (app. 0.25 x wavelength) and the diameter of the coils (app. 1/3 of the wavelength) determine its wavelength. The length of the coil determines how directional the antenna will be and its gain; longer antennas will be more sensitive in the direction in which they point. A reflector R is almost always used to increase the sensitivity, or gain, in one direction (away from the reflector).