Wide-band measurement of complex permittivity using an overmoded circular cavity

Abstract

A large terminating circular cavity structure is proposed in this paper for measuring the complex permittivity of low-loss dielectric materials over a very wide frequency range of 20–100 GHz. Compared to many other widely used configurations employing off-resonant circular cavity, this new overmoded circular cavity provides higher precision of relative permittivity results and a wider frequency range. Extensive measurements are carried out and measured results for two sample materials are presented. An inverse algorithm using the mode-matching method is introduced to calculate the complex permittivity of the dielectric sample. An error analysis is also presented to estimate the errors incurred due to the uncertainty in the S-parameter measurement, sample size, location of the coupling probe.