A compact dual-mode single-resonator DGS microwave sensor for self-referenced permittivity characterization

This paper presents a compact microwave sensor for permittivity characterization based on a single defected ground structure (DGS) resonator with an intrinsic dual-mode response. Unlike conventional differential sensors that require two physically separated resonators, the proposed design exploits two resonant modes intrinsically generated by a stub-loaded double split-ring resonator to enable internal referencing within a single compact structure, thereby eliminating inter-resonator mismatch issues and reducing the sensor footprint. The lower-frequency mode exhibits weaker interaction with the sample under test than the sensing mode and acts as a common-mode reference, whereas the higher-frequency mode shows strong electric-field confinement in the sensing region and is used for permittivity sensing. A prototype was fabricated on a Rogers RO4003 substrate and experimentally validated using several solid dielectric samples. The measured results show a normalized sensitivity of 1.41% and a coefficient of determination of R 2 = 0.9814, in good agreement with full-wave simulations. Owing to its compact size, single-resonator implementation, and self-referenced operation, the proposed sensor is suitable for non-destructive dielectric characterization.