A Miniaturized X-band High-Index Supercavity Resonator in Microstrip Technology

We present the first supercavity-mode high-index resonators excited by microstrip structures at X-band. Supercavity modes are attractive for trapping energy in high-quality subwavelength resonators. Previously this localization option was only demonstrated in three-dimensional resonators in the RF regime. Enabling such modes in planar technologies requires significant miniaturization and novel coupling structures that can excite the required nonorthogonal mode pairs. This work addresses both of these challenges for the first time. Specifically, we employ microstrip resonators to excite hybrid supercavity modes. We also demonstrate the robustness of the presented design with respect to fabrication uncertainties. Furthermore, we employ microstrip high-index resonators (HIR) with dielectric constant of 140. A proof-of-concept resonator with volume of less than 3.45×10⁻⁴λ³ and first supercavity resonance of 11.2 GHz with a measured unloaded quality factor of 204 is demonstrated. This is the highest reported quality factor in planar-excited supercavity technology with the above-mentioned volume.