Evaluation of the frequency dependence of the complex conductivity of a resistive chamber by comparing theoretical and measured -matrices

Shobuda, Yoshihiro   

For an accurate calculation of the resistive-wall impedance of a resistive chamber, we must know the conductivity of a resistive material. The conductivity of the material at a given frequency can be evaluated by measuring the -matrix of a propagation mode in a waveguide. However, in most cases, only the absolute value of the -matrix is used for evaluation under the assumption that the conductivity is pure real, although both the -matrix and the conductivity are complex numbers in general. To evaluate complex conductivity from a measured complex -matrix, we derive new theoretical formulae of the -matrix for the TE and TM modes of a waveguide and for the quasi-TEM mode of a coaxial waveguide, where complex conductivity is assumed. In a reverse way, we can determine the conductivity of a material by using it as a fitting parameter in a comparison of a measured -matrix with those obtained using theoretical formulae. The three independent methods facilitate triple-checking of the accuracy of the measured conductivity.