Some effects of field perturbation upon cavity-resonance and dispersion measurements on MIC dielectrics

The paper analyzes field perturbations in MIC resonators, with consideration of the Q factor, coupling effects, fringing fields, crystal misalignment (for anisotropic materials) and changes in ambient temperature. Analysis of a cavity with mixed boundary conditions shows that resonant-mode frequencies depend to the first order on that part of the unloaded Q associated with imperfect metal walls, but to the second order on that part associated with imperfect open-circuit walls. A new expression is given for the Q of an open-ended microstrip resonator when surface waves are excited in the dielectric. These procedures, which can be applied to the analysis of permittivity measurements made by cavity-resonance methods, lead to revised values for the crystal permittivity of sapphire in the microwave region.