Circularly polarized edge-placed printed monopole antenna using theory of characteristic modes

This article presents a method of using modal analysis to characterize the circular polarization (CP) performance of a printed monopole antenna. The radiator and feedline are positioned on the edge of the substrate and fed accordingly at the edge, and a modified ground plane is employed. The complete antenna without excitation is analyzed using characteristic mode theory to provide physical insight into its CP operation. The modal analysis proves that several nearly orthogonal modes can be generated at certain frequencies with orthogonal phase differences as well. The axial ratio (AR) corresponds to the modal analysis which proves the validity of the modal analysis. An axial ratio bandwidth from 3.1 to 6.2 GHz (66. 7%) is achieved within an S-11 bandwidth of 2.6-11 GHz (123.5%). The proposed antenna is compact with stable radiation patterns, easy to design, and fabricate without inserting parasitic patches or inserting slots on the antenna.