Circularly Polarized Square-Ring Antenna Loaded With Reactive Components

In this study, a novel, simple single-feed square-ring antenna is proposed for circular polarization (CP) operation. The design procedure involves three stages. In the first step, a conventional square-ring antenna is loaded with an open gap at specific locations along the square ring. This antenna exhibits two resonance characteristics (f₁ and f₂) with polarizations orthogonal to each other. This antenna works as a dual-band dual-linear polarized antenna. In the second step, the second resonant frequency (f₂) is controlled without varying the first resonant frequency (f₁) by embedding a lumped-chip capacitor/inductor in the open gap of the square-ring antenna. Therefore, the antenna has a tunable frequency ratio (f₂/f₁). By choosing a suitable lumped element, two proximal resonant frequencies are obtained, and two orthogonal resonant modes with a 90° phase difference are excited. Finally, pure CP is obtained. In the last stage, a lumped element is realized using a distributed element. Numerous prototypes of the proposed antenna are implemented, and their performance is measured. The measurement results show that radiation patterns with good CP characteristics are obtained at the resonant frequencies.