Modeling of Passive Intermodulation in Coaxial Connectors With Ideal and Nonideal Contacts

Passive intermodulation (PIM) in radio frequency (RF) pathways can arise from multiple factors, including the passive nonlinear effects inherent in coaxial connectors. This study develops models to characterize PIM behaviors under both ideal and nonideal contact conditions, specifically addressing the scenarios of oblique and shallow insertions. Finite element analysis (FEA) was employed to construct models that assess the current density distribution at the contact interfaces, considering both transverse and axial cross sections of the central conductors. In the transverse cross section, the contact radius is determined by the applied pressure, whereas in the axial cross section, the contact length correlates with the insertion depth. A PIM model was derived based on the peak current density at a localized contact area (a-spot). Customized connector samples were utilized for PIM testing. The consistency between predictions and measurements, confirmed through repeated insertions and withdrawals, substantiates the instability of PIM arising from nonideal connections within the connectors.