Wideband Circularly Polarized Quadrifilar Helix Antenna With Hemispherical Coverage

This paper presents a wideband circularly polarized quadrifilar helix antenna (QHA) featuring simultaneously wide 3-dB axial ratio beamwidth (ARBW) and half-power beamwidth (HPBW), addressing the conventional trade-off between bandwidth and beamwidth. The antenna comprises four pairs of three- stage stepped-impedance folded helical arms, collectively loaded with an arc-shaped metal ring on top. The three-stage stepped-impedance folded helical arm effectively enhance the bandwidth while maintaining a wide HPBW, and the arc-shaped metal ring further broadens the 3-dB ARBW across the wide band. To validate, a prototype was fabricated and measured. Measurements show that the bandwidths corresponding to 10-dB return loss and 3-dB AR reach 44.2% and 35.2%, respectively. Moreover, within a 17.4% bandwidth, the measured HPBW and 3-dB ARBW vary from 132° to 152° and 179° to 265°, respectively, demonstrating its suitability for wideband circularly polarized applications with broad beam coverage and robust AR performance.