Selection of ferrite materials for microwave device applications

This paper deals with some general rules for selecting materials for linear ferrite devices. Four steps are required for material definition. 1) An analysis which relates device performance to the intrinsic complex permeability tensor [μ] and to the complex permittivityε = epsilon' - jε"of the material. 2) A determination of the internal biasing field in the ferrite from the applied biasing field and shape-dependent demagnetizing factors. 3) An estimate of the required saturation magnetization Msbased on a consideration of lowest operating frequency, peak RF power level, and maximum desirable biasing field. 4) A specification of ferrite composition and mechanical properties resulting from consideration of magnetic loss, temperature-dependence of the device, peak-power capability, and mechanical stability. Materials selection is done from the particular ferrite system which comes closest to the required saturation magnetization and offers the best compromise with respect to magnetic loss, temperature stability, and peak-power handling capability.