Orthogonal Resonators for Circularly Polarized Filtering Antenna Using a Single Feedline

Polarization diversity is an antenna feature that has been widely researched to increase the capacity of a wireless communication system. The conceptual theory of polarization states that all polarization vectors can be decomposed into two orthogonal electric field vector modes. This study proposes a novel framework to bridge the gap between circular polarization (CP) technique and filtering antenna design using two orthogonal resonators with the ability to represent any polarization. The proposed method combines the techniques of antenna&#x2013;filter and CP design into a single integrated step. To achieve the second-order antenna&#x2013;filter integration and generate CP, the two orthogonal resonators modeled as a rectangular radiator and a <inline-formula> <tex-math notation="LaTeX">$\uplambda $</tex-math> </inline-formula>/4 resonator combined. The CP filtering antenna operates at a frequency of 4.65 GHz, with an impedance bandwidth of 4.7%, an axial ratio (AR) bandwidth of 3.2%, and a gain of 6.2-dBi. To validate the CP filtering antenna, simulations and measurements were performed, and the results were found to be in good agreement.