A three-dimensional circularly polarized antenna with a low profile and a wide 3-dB beamwidth

Abstract

An improved three-dimensional circularly polarized quadrifilar helix antenna (QHA) with low profile and wide 3-dB beamwidth is proposed and its performance is investigated both numerically and experimentally. The proposed modified QHA is comprised of a short-circuited quadrifilar helical antenna printed on a thin FR4 substrate, with its four ports terminated by 50 Ω resistances. In addition, four monopoles with 90° phase progression are positioned around the quadrifilar helical antenna, and four Archimedean spirals are used to top-load the monopoles. Simulated and measured results show that the proposed antenna achieves a bandwidth of 23.8%, has a 3-dB beamwidth greater than 170°, and its axial ratio is less than three in the entire upper hemisphere over a wide frequency band.