Design of Circularly-Polarized Filtering Antenna Using Characteristic Mode Theory

A circularly polarized filter antenna (CPFA) is designed using Characteristic Mode Theory (CMT). Firstly, the mode distribution between adjacent patches is analyzed. By adjusting the patch size, the $\mathbf{T M}_{10}$ and $\mathbf{T M}_{01}$ modes are separated. Then electrical coupling is introduced between the two patches to produce the filtering performance. Finally, the appropriate feed position is determined by analyzing the mode electric field distribution. The simulated results indicate that the antenna can work at $2.91-3.14 \text{GHz}(7.6 \%$ bandwidth) and achieve circular polarization effect in the range of $2.995-3.017 \text{GHz}$.