Frequency dependence measurements of complex permittivity of a dielectric plate by using TE0m1 modes in a circular cavity

A circular cavity resonance method is improved to measure the frequency dependence of complex permittivity of a dielectric plate by using multimode TE0m1 with integer m of the higher order. The measurement principle is based on a rigorous analysis by the Ritz-Galerkin method. A new circular cavity with lowered height is designed to decrease the number of unwanted modes near the TE0m1 modes from a mode chart of a cavity. Then the frequency dependence of a glass cloth PTFE dielectric plate is measured over the frequency range 15∼35GHz by using TE0m1 (m=1, 2, 3, 4) modes in a circular cavity designed at 20GHz for the TE011 mode. The measured results are compared with ones measured by using the conventional four different size cavities with TE011 mode. It is verified that the designed cavity structure is useful to measure the frequency dependence of a dielectric plate.