Characterization of Y-Bias Ferrite Materials for Tunable Antenna Applications Using a Partially Filled Rectangular Waveguide

A methodology for measuring the constitutive parameters of a ferrite material is presented. This method can be used to assist the prediction of the properties of tunable antennas that use ferrite material as a substrate or tuning component. A nontraditional characterization method is required due to the general unavailability of samples of a sufficient size to fill the entire cross sections of waveguides appropriate for lower frequencies where gyromagnetic properties are most pronounced, and the difficulty of predicting or approximating the applied bias magnetic field. The proposed method overcomes the limitation of sample size by requiring only partial filling of a rectangular waveguide. It overcomes a lack of knowledge of the bias field by including the field as an unknown to be determined by the extraction process. The required theoretical reflection and transmission coefficients of the partially filled waveguide are determined using a mode-matching technique. A nonlinear least squares method is employed to extract the gyromagnetic material parameters and the bias field using optimization algorithms in MATLAB. The extracted parameters of a representative commercial ferrite obtained from multiple experimental configurations are compared with the values provided by the sample manufacturer to demonstrate the feasibility of this technique.