Effect of second harmonic and second-order intermodulation on third-order passive intermodulation

Third-order intermodulation (IM3) is considered as a typical metric to evaluate passive intermodulation (PIM) in electrical connectors, which may be affected by the second-order effect in the circuit with cascaded non-linearities. In this study, the effects of second harmonics and second-order intermodulation on the IM3 powers were theoretically modelled and experimentally verified. Combined with mathematical modelling, an equivalent circuit model of a passive non-linear source was presented to investigate the effect of second-order signals on the IM3 powers. A modified non-linear transfer function was developed by considering multiple non-linear superpositions in cascaded non-linearities. Based on the designed two-tone test, a mathematical expression was provided with the determination of correlation model coefficients. Numerical simulations were performed by using the proposed model, demonstrating the effect of signals induced by the second-order non-linearity on the IM3 powers in series passive components. The IM3 powers resulting from cascaded connectors associated with different signal frequencies were predicted. Coaxial connector samples were designed as cascaded PIM sources in circuits, which were experimentally measured in a GSM 900 MHz frequency band. Good agreement was obtained between the predictions and measurements with error of 0.76 dB in average.

Automated summary

In this study, the effects of second harmonics and second-order intermodulation on the IM3 powers were theoretically modelled and experimentally verified. A modified non-linear transfer function was developed by considering multiple non-linear superpositions in cascaded non-linearities. Numerical simulations were performed to demonstrate the effect of signals induced by the second-order non-linearity on the IM3 powers in series passive components.