Horizontally and Circularly Polarized Omnidirectional Filtering Dielectric Resonator Antenna

This paper presents a horizontally polarized (HP) omnidirectional filtering dielectric resonator (DR) antenna (DRA) and its circularly polarized (CP) counterpart, without extra filtering circuits. The HP filtering DRA comprises a DR and a single-layer circular substrate. A modified end-shorted Alford loop with center-shorted parasitic strips is positioned on the top of the substrate, two concentric circular slots are etched on the bottom. Wherein, the inner slot consists of four open stubs. This configuration excites three operating modes: the TE011+δ DR mode and two patch modes. Through mode cancellation between these modes, two radiation nulls are created near the passband, thus realizing filtering responses. The CP filtering design shares a highly similar structure with the HP one. The key difference lies in its bottom side, which features a single circular slot integrated with both open and shorted stubs. This setup enables filtering responses with left hand circular polarization (LHCP). Both the HP and CP filtering designs were fabricated and measured. The HP DRA features a measured -10-dB impedance bandwidth of 19% and a realized gain of 1.25 dBi within the passband. It has an electrical size of π×0.252×0.19λ03. The CP design has an overlapped -10-dB impedance and 3-dB axial ratio (AR) bandwidth of 11.9%, with a realized gain of 0.7 dBic. Whereas, its electrical size increases to π×0.282×0.18λ03. Both designs show omnidirectional radiation patterns with suppression levels over 19 dB and 13.3 dB, respectively.