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

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 resistances. In addition, four monopoles with 90 degrees 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 degrees, and its axial ratio is less than three in the entire upper hemisphere over a wide frequency band.