Dielectric-Loaded Microwave Rectangular Waveguide and Higher Order Mode Resonator

Resonant transmission through a dielectric-loaded slot in a thick conducting diaphragm embedded in a rectangular waveguide is modeled using an analytical approximation based on the slot being small compared to a free-space wavelength. An image theory relates this problem to a metasurface consisting of an array of such slots. We demonstrate the existence of ordinary (Fabry-Perot) transmission resonances associated with the fundamental mode of the slot, as well as extremely narrowband (Fano) resonances involving the higher order modes in the slot. The theoretical predictions are confirmed through full-wave numerical simulation and by experimental measurement. Measurements on dielectrics consisting of multiple pieces reveal an additional set of sharp resonances, not predicted by our theory but verified by finite-element simulation. The results have potential application to sensors and material property measurement.