Characterization of a spherically symmetric fused-silica-loaded cavity microwave resonator

Whispering spherical modes in a fused-silica-loaded cavity with spherical symmetry are characterized and reported. The fundamental mode families of the transverse electric and transverse magnetic whispering gallery modes are measured and the loss tangent of the fused silica determined as a function of frequency in the 3–12 GHz regime. The temperature dependences of mode frequency and quality factor were determined between 6 and 300 K. The relative permittivity and loss tangent for fused silica at 5.18 GHz were determined between 6 and 300 K. Below 22 K the frequency dependence of the 5.18 GHz TM212 mode of resonance was consistent with the combined effects of the thermal properties of the dielectric and the temperature dependence of an unknown paramagnetic impurity ion, which has a spin resonance frequency at about 138 ± 31 GHz. Below 8 K the loss tangent exhibited a ninth-order power-law temperature dependence, which may be explained in terms of Raman scattering of phonons from the paramagnetic impurity ions