Sub-1 GHz Temperature-Tunable Linear-to-Circular Polarization Converter Using a Cost-Effective Water-Based Periodic Structure

Linear-to-circular polarization converters find applications in modern 5G and 6G communication systems, satellite communications, and the Internet of Things paradigm. A cost-effective three-dimensional frequency-selective surface that uses water as the active material and silicone rubber as the container is proposed. The operation of the design in the 0.1–1 GHz frequency range is assessed through full-wave simulations. Field distribution maps are employed to elucidate the underlying resonance mechanisms. The stability of the proposed structure with respect to the angle of incidence and frequency is evaluated. A quasi-linear variation of the operating frequency with temperature is demonstrated, enabling temperature tunability. The proposed solution is suitable for prototyping, demonstration, and educational purposes in an eco-friendly context.