Numerical analysis of a TM010 cavity for dielectric measurement

The properties of a TM₀₁₀ cavity containing a lossy dielectric material are investigated, using the transmission-line-matrix (TLM) technique with serial nodes in cylindrical coordinates. The cavity operates at 1.1 GHz and has three concentric layers and an air gap between the sample and cavity cover. The influence of this air gap on the Q-factor and the resonant frequency is studied. Compared with the TLM method in rectangular coordinates and uniform grids, the present method is more efficient and easier to program for the analysis of the cavity with cylindrical symmetry. Computed results show that the air gap between the sample and cavity cover is very critical to the accuracy of the measurement of the dielectric property of the sample when the sample diameter is small, but negligible when the diameter is large. Unfortunately, in the case of a highly lossy sample, a small sample diameter must be used to maintain a reasonably high Q-factor. Special techniques are recommended to minimize the error caused by the air gap