Transfer matrix theory for Passive Intermodulation of microstrip lines

Abstract:

The uniform microstrip line is the basic structure of the microstrip circuit, and it is of great significance to establish the Passive Intermodulation(PIM) analytical model of the microstrip line. Based on the controlled source equivalence, in the lumped circuit equivalent model of the microstrip line, the distributed parasitic nonlinear PIM source in the microstrip line is modeled as a second controlled current source or voltage source, to obtain the matrix expression of the relationship between the voltage and current in the stripline PIM. The analytical calculation model of the uniform microstrip line PIM with the parasitic nonlinear mechanism is finally established. The experimental verification is carried out by comparing the transmission intermodulation and reflection intermodulation laws of nickel-plated microstrip lines with different lengths and nickel-plated microstrip lines with different concentrations of phosphorus doping. The third-order relative permeability nonlinear coefficient of nickel coatings is extracted to be 1×10^-10 m2/A2 at 0.71 GHz. The proposed method based on controlled source equivalence provides a new idea for further establishing PIM models of other microstrip circuits.