Modeling of Passive Intermodulation in Connectors With Coating Material and Iron Content in Base Brass

Ferromagnetic materials in coaxial connectors are one of the main contributors to passive intermodulation (PIM) in radio frequency systems. In this paper, the effects of coating materials and iron content in base brass on PIM performance were theoretically modeled and analyzed, and the results experimentally verified. A finite-element analysis model for a cross section of the inner conductor was developed to evaluate the current density distribution in connectors with different materials, coating thickness, and iron content in the base copper alloy. Simulation calculations were performed to study the nonlinear characteristics induced by ferromagnetic materials in the communication frequency band. The relationship between the PIM products power and the current density distributions was investigated based on the theory of microwave electromagnetic fields and nonlinear mathematical modeling. This model was used to theoretically predict the intermodulation (IM) products power resulting from connectors with various material properties. In addition, a series of experiments based on two-tone testing was conducted to measure IM products of specific connectors. Good agreement was observed between experimental measurements and the predictions of the analytical model, validating the PIM analysis method and results.