Cavity perturbation technique for the measurement of permittivity tensor of uniaxially anisotropic dielectrics

Based on microwave resonant perturbation theory, a bimodal TE₁₁₂ cylindrical cavity is developed for the measurement of permittivity tensor of uniaxially anisotropic dielectrics. The two perpendicular TE₁₁₂ degenerate modes in the cavity are used to measure the two complex components in the permittivity tensor of a uniaxial sample, respectively. In the measurement of each component, only the corresponding mode resonates in the bimodal cavity, and the real and imaginary parts of the complex component are deduced from the changes of the resonant frequency and the quality factor of the cavity due to sample insertion. In the present technique, the quality factors of the cavity before and after sample insertion are measured at the same frequency, so the uncertainties caused by the variation of the total stored energy in the cavity due to sample insertion are eliminated. Experimental results show that the present technique is accurate and reliable for the measurement of the permittivity tensor of uniaxial media. As an example, the dielectric properties of α-SiO₂ samples with different crystal orientations are characterized using the present technique