Investigation of an End-Fire Circularly Polarized Antenna Based on Normal-Mode Helix

This paper investigates a Yagi antenna with circular polarization (CP) at the end-fire direction based on normal-mode helix. It consists of a right-handed center-fed helical dipole and two parasitic helixes with the same direction of rotation. The parameters of the driven helix are optimized to realize circular polarization and quasi-uniform radiation in the plane normal to the helix axis. The coupling between the driven and parasitic helixes is utilized to achieve a unidirectional radiation. It is found that an end-fire beam with CP is obtained by carefully choosing the parameters of the parasitic helix and the spacing between them. Simulation results show that the final optimized antenna achieves a gain of 6.4 dBic and front-to-back ratio of 8.1 dB at 1 GHz.