Whispering-gallery modes of dielectric resonators

The whispering-gallery modes of cylindrical dielectric resonators of high permittivity (er~38) are investigated. Axial-mode confinement is ensured by a slight increase in the rod diameter. The resonances for various azimuthal mode numbers and the two states of polarisation are identified experimentally. There is a good agreement between measured and calculated frequencies. The measured quality factor, of the order of 7000 at 6 GHz, is, for some resonances, limited only by the intrinsic loss of the dielectric material. The whispering-gallery mode of resonance enables designers to use comparatively larger-size dielectric resonators at millimetre-wavelengths with good frequency selection and low loss.