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.