<title>High-frequency characterization of dielectrics using open resonators</title>

Abstract

Open planar resonators like rectangular and triangular microstrip resonators and slot resonators can be used to determine the dielectric constants of lossy or lossless dielectrics at microwave and millimeter-wave frequencies. These resonators can also be used to measure the thickness of dielectric slabs. In all cases, the accuracy of the method depends on the theoretical information available for the inversion of the measured data. In this paper, a general accurate pseudo-numerical technique for the analysis of single and multi-layer open planar resonators loaded with dielectric slabs is given. The technique can be used to obtain inversion curves. In the case of the microstrip resonator, coupling to the signal source is assumed to be through a coaxial probe or through a microstrip line, whereas in the case of the slot resonator, a microstrip line feeds the resonator. The technique is applied to specific cases of single and double layer microstrip resonators of rectangular and triangular shape in order to compute the shifts in the resonant frequency and changes in the input impedance when these resonators are subjected to various lossy and lossless dielectric materials of different thicknesses. Sample results are presented and discussed. In particular, it is shown that the double layer resonator offers some advantages in the measurement of the shift of the resonant frequency as one of their two resonant frequencies (i.e., the upper resonant frequency) seems to be almost independent of the dielectric loading, and hence can be used as the frequency reference.