Resonant Frequency of Superposed Dielectric Resonators: Application to the Determination of the Local Dielectric Permittivity of M.I.C. Substrates

Several methods have been described to measure the permittivity of dielectric substrate, and all used the complete area of the sample and so give an average value of this parameter. But in the realization of microwave integrated circuits it is important to know dielectric parameters of the substrate at the point where the component is located. For this local characterization, we propose a method in which the substrate is in sandwich between two similar dielectric resonators. This non destructive method permits to determine the permittivity of a small area (few mm2) of the substrate, by comparing the measured and calculated resonant frequencies of the studied structure.