Impact of Signal Frequency on Passive Intermodulation in Coaxial Connectors

Passive intermodulation (PIM) from coaxial connectors can be a significant problem in the transmission of high frequency signals. A major source of this effect is nonlinearity resulting from magnetic materials in the connector fabrication. The PIM performance of a given coaxial connector is, generally, different at different frequencies. As communication frequency bands become denser, developing a better understanding of the passive intermodulation characteristics of coaxial connectors at different frequency bands and using that knowledge to improve connector designs becomes a critical concern. Accordingly, this research seeks to provide a theoretical basis for evaluating PIM performance in coaxial connectors at different frequency bands. In this study, passive intermodulation was analyzed from the perspective of material nonlinearity, with the magnetic material in the coaxial connector coatings considered as the source of the nonlinearity that drives this effect. The current flowing through the magnetic region in a sample coaxial connector configuration was simulated by finite element analysis for a variety of frequency bands. Combined with skin effect theory, the impact of signal frequency on PIM in coaxial connectors was investigated and modeled. The results from this model were validated with experimental tests. Specifically, a multi-band PIM test system was used to measure the third-order intermodulation product power of sample coaxial connectors with input signals from different frequency bands. The corresponding model results and the experimental results show good agreement.