An Improved Cavity-Perturbation Approach for Simultaneously Measuring the Permittivity and Permeability of Magneto-Dielectric Materials in Sub-6G

Magneto-electric materials with low loss have prospective applications in microwave systems as they enable miniaturization and broadband impedance matching. Two example applications are antennas and filters in sub-6G communication systems. Therefore, high-accuracy and wideband testing are critical for magneto-electric materials, whose complex permittivity and permeability are usually dependent on frequency. In this paper, the mutual interference between the electric and magnetic field within magneto-electric material samples was seriously considered. It was found that the results calculated with the original perturbation formula were overestimated when the sample size was not so small or higher-order modes are used, especially when the electric or magnetic field is perpendicular to the material under test. Two methods based on perturbation, namely the iteration method and the multi-state method are proposed to reduce the impact of the mutual interference, which have been proven to be direct and effective through theoretical analysis and experiments. Finally, several rod-shaped specimens processed from several standard dielectric materials (PTFE, fused silica, Al2O3) and synthesized magneto-electric materials were measured in a fabricated cavity with a vector network analyzer. Experimental results show that the results obtained by the modified formula are more accurate than those obtained by the original formula, and are in good agreement with the data measured by other methods.