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Wideband Omnidirectional Circularly Polarized Patch Antenna Based on Vortex Slots and Shorting Vias

A wideband omnidirectional circularly polarized (CP) microstrip antenna is proposed. The proposed antenna is composed of a disk-loaded coaxial probe, six shorting vias and a circular patch with six vortex slots. Three resonant modes, which include the TM01, top-loaded monopole and TM02 modes, with conical radiation patterns can be simultaneously excited in the antenna structure by a disk-loaded coaxial probe through capacity coupling, and they can be coupled together to realize a wideband operation. Six shorting vias, located symmetrically about the center of the patch, are introduced for generating the θ-polarization and six vortex slots are employed for obtaining the φ-polarization. Omnidirectional CP fields can be obtained at all these three resonant modes when the two orthogonal polarizations are equal in amplitude but different in phase by 90°. Both the wideband and CP principles are analyzed and verified by the parametric study. The obtained results show that the wideband CP antenna has a 10-dB impedance bandwidth of 51.7% and a 3-dB axial ratio (AR) bandwidth of 57.8%. In addition, a comparison between the proposed wideband antenna and the related wideband CP antennas in the literature is made.