A Novel Single-Feed Dual-Element Antenna Using Phase Compensation and Magnitude Regulation to Achieve Circular Polarization

This paper investigates the design of a novel single-feed dual-element antenna that can be used to achieve circular polarization (CP) performance for mobile devices at arbitrary locations. The severe conditions needed to achieve CP remain as difficult issues for small mobile antennas; this is the case because the ground plane, rather than the antenna structure, contributes to the dominant radiation as the antenna volume shrinks. A novel concept of decomposing the antenna into two elements, which are independently coupled to two orthogonal ground modes for far-field radiation, is proposed through a theoretical analysis based on characteristic mode theory. The proposed dual-element antenna is comprised a loop-type element and monopole-type element, where one element is directly fed and the other resonates parasitically. In this way, the magnitudes and phase difference between two radiated field components can be controlled through antenna tuning without needing to manipulate the ground plane. Both simulations and measurements are conducted to verify the proposed antenna design with a widely used smartphone.