An omni-directional circularly polarized antenna with a low profile and wide axial-ratio beamwidth

A novel low profile omni-directional circularly polarized (CP) antenna with wide axial-ratio (AR) beamwidth in the elevation plane is proposed. It is composed of a compound vortex radiator, a ground plane, and two groups of vias. By adjusting the structure of the compound vortex stub, |E|=|E-phi| is realized in a wider range of . Also, the 90 degrees phase difference between E and E-phi is obtained by regulating the size of a sector patch at the end of the vortex stub. The measured results show that the proposed antenna has an impedance bandwidth of 3.2% (3.03-3.13 GHz) and a 3 dB AR bandwidth of 21.6% (2.5-3.17 GHz). Also, the 3 dB AR beamwidths at 3.10 GHz are 270 degrees and 274 degrees in the phi=0 degrees and phi=90 degrees planes, respectively. A good agreement between the simulated and measured results is obtained.