Square Waveguide Cavity for Complex Permittivity and Permeability Measurement by Perturbation Method Without Repositioning

Abstract

This article presents a novel configuration for the simultaneous complex permittivity and permeability determination with only a single sample placement inside the resonant cavity. The proposed structure incorporates two waveguide orthomode transducers (OMTs) and a square cavity. The square cavity is designed to overcome the limitation of permeability measurement by the rectangular cavity perturbation method. These components allow the product of two orthogonal transverse electric (TE) resonant modes (TE10L and TE01L) with the same cutoff frequencies. Based on Maxwell equations and perturbation theory, new relations are developed to characterize the complex permeability of specimens at TE01L modes. The proposed structure eliminates the main drawbacks of previous studies such as depolarization effect of partial-height samples, radiation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> -plane sample hole, need to apply the sample holder and precision positioner, multistate positioning, iterative calculations, extra calibration process, and employing complicated mathematical equations. The proposed configuration was designed using CST Microwave Studio (MWS) and ANSYS high-frequency structural simulator (HFSS) and then manufactured and measured. The operating frequency has been selected from 7.5 to 12.5 GHz. Good agreement is achieved between measurement and simulation. The performance of the developed structure was verified by measuring the material characteristics of bar-shaped dielectric and magneto-dielectric specimens and compared with other studies.