Characterization of microwave substrates with split- cylinder and split-coaxial-cylinder resonators

Abstract

Two types of split-cylinder resonators are used for characterization of the longitudinal dielectric parameters of reinforced RF substrates. The novelty of the method is the introduced theoretical 3D model of the measurement cavities, which allow determination of the parameters with the help of arbitrary 3D electromagnetic simulators. Two known isotropic and anisotropic materials are measured with circular and splitcylinder resonators and the results are compared. One of the considered structures -the split-coaxial resonator with movable inner post cylinder -allows substrate measurements at lower frequencies compared with the resonance frequency of the ordinary split-cylinder resonator. I. INTRODUCTIONThe split-cylinder resonator is a popular nondestructive measurement tool for material parameters' characterizationdielectric constant ε r and dielectric loss tangent tanδ ε [1]. Compared with the ordinary non-split cylindrical resonator, it consists of two equal cylindrical parts and a radial-line section, where the parallel-surface sample is placed - Fig. 1a, b. The obvious advantage is that no special sample has to be prepared -the measured material has to cover the resonator diameter with ~10-% in reserve. The role of the cylindrical part in the structure might be different. In Kent's evanescentmode tester [2] the cylinder acts upon a cut-off waveguide and the EM fields can't deeply penetrate into the cylindrical part. The resonance is formed mainly by a part of the sample in this case, which forms an equivalent dielectric resonator [3]. The split-resonator can be described in this case by the simplest theoretical model. This structure is more suitable for characterization of relatively high-permittivity materials (ceramics, ferrites, semiconductors). Contrariwise, when the cylinder has relatively big diameter, the resonance behaviour of the splitcylinder resonator with sample becomes more complicated and a full-wave analysis of the structure is necessary. The fringing-field effect can be accurately taken into account by the mode-matching technique [4] and therefore, the splitcylinder resonator method becomes convertible for broadband measurements of low-permittivity, low-loss materials using the TE 011 or the high-order TE 0nm modes [5].We propose in this paper a new theoretical approach applicable to any split-cylinder resonance structure -we introduce 3D models of these open resonators, suitable for simulation through the standard FEM-or FDTD-based simulators. This approach is quite universal and allows utilization of more complicated open-type resonance structures for measurement purposes easily solving the problem of the fringing-field effect

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