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 TE_0m1 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 TE_0m1 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 TE_0m1 (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.