Amendment of cavity perturbation method for permittivity measurement of extremely low-loss dielectrics

The quality factor of a resonant cavity may increase after introducing an e xtremely low-loss dielectric, so the conventional cavity perturbation metho d, widely used in dielectric permittivity measurement, may be invalid for e xtremely low-loss dielectric samples. After a brief review of the conventio nal cavity perturbation theory, this paper discusses the change of quality factor of a resonant cavity due to the introduction of a dielectric sample, A new concept, expected quality factor Q(0), is introduced in this paper t o denote the quality factor of a resonant cavity loaded,vith a strictly no- loss sample, and a calibration procedure is proposed to find the frequency dependence of Q(0) The conventional resonant perturbation formulas are then amended by substituting the quality factor before the perturbation with th e expected quality factor Q(0) corresponding to the frequency after the per turbation, Experiments show that the accuracy of resonant perturbation meth od has been greatly increased after the amendment, especially for extremely low-loss dielectric samples.