Measurements on alumina and glasses using a TM020 mode resonant cavity at 9.34 GHz

Small samples of dielectric, typically obtained from flat substrates, are conveniently prepared by slicing the substrate into rods with square cross-sections. The paper investigates a method for measuring the permittivities of dielectrics in this form, and gives the appropriate analysis for such rods in a TM020 mode cavity. A reliable check is provided by using samples with circular cross-sections, for which the analysis is fully established. For the glass samples, the agreement between the two methods is good, but, with alumina, problems arise owing to the anisotropic nature of the polycrystalline samples used. It is suggested that, when comparisons are made between different microwave techniques for permittivity measurements on polycrystalline alumina, further investigations are required on the distribution of crystallographic directions within the samples used.