Measurement of intrinsic nonlinear parameters for microwave ferromagnetic materials using coated transmission-line and LNS-FDTD methods

This work proposes two methods for evaluating the intrinsic nonlinear parameters for the microwave ferromagnetic materials, which play an important role in the development of low passive-intermodulation devices. We find that the product of the nonlinear permeability and the skin depth serves as the intrinsic nonlinear parameter governing the passive intermodulation (PIM) effect. Analytical and numerical models are proposed to extract it from the experiments. For the coated transmission line method, an analytical expression for the relationship between PIM and the nonlinear parameter is derived. For the linearity–nonlinearity-separation (LNS) Finite Difference Time Domain (FDTD) full-wave method, a PIM simulation algorithm suitable for thin coating layers is established. Both methods are validated using a nickel-plated microstrip line. The extraction results from the two approaches are in good agreement, confirming the consistency and feasibility of the proposed measurement methods.