Compact Normal-Mode Hybrid-Helix Antenna and Its Application to Circularly Polarized Yagi Array

This communication presents a compact normal-mode hybrid-helix antenna of circular polarization and its Yagi array configuration. By cascading two types of helices with different turn spacings and radii, the hybrid-helix antenna element effectively alleviates the limitation of the traditional normal-mode helix antenna that is challenging to simultaneously achieve circular polarization and high radiation efficiency. The proposed hybrid antenna element is also further extended for a Yagi array to obtain the endfire circular polarization. For experimental verification, the hybrid-helix array is fabricated using the selective laser melting (SLM) technique. Measured results agree well with simulated ones, showing that the impedance of the normal-mode helix array can cover the 10 dB impedance bandwidth from 2.27-2.47 GHz, and the axial ratio of less than 3 dB and the radiation efficiency of higher than 90% can be achieved within the whole operating bandwidth.