Substrate integrated waveguide resonator sensor for X-band dielectric constant characterization

This work presents the design, simulation, and experimental validation of a compact single-port microwave sensor based on substrate integrated waveguide technology. The proposed sensor consists of a circular resonant cavity implemented in a substrate integrated waveguide, with a rosette-shaped slot etched into the top copper layer to enhance electric field confinement in the sensing region. This configuration enables the accurate characterization of low-permittivity materials in the X-band frequency range. The reflection response S11 of the sensor is analyzed for various materials, including air, Teflon, and Plexiglas. The results show a clear resonance frequency shift depending on the permittivity of the material, with measured sensitivities of about 5.85% for Teflon and 3.65% for Plexiglas. The proposed structure shows good agreement between the simulation and the measurement results, as well as non-destructive characterization of dielectric properties, as the material under test is not physically or chemically altered during the measurement process.