Linear–Nonlinear Interaction and Passive Intermodulation Distortion

This paper describes several consequences of a linear-nonlinear interaction that was recently found to be of importance in microwave circuits that produce passive intermodulation (PIM) distortion. This paper briefly discusses how this linear-nonlinear interaction operates in an example system. It then discusses how an understanding of the linear-nonlinear interaction allows us to distinguish between different types of nonlinearities from the power dependence of the third-order intermodulation distortion product. Next, an example uses a multiphysics simulator to demonstrate that electrothermal nonlinearities behave as expected from the linear-nonlinear interaction model. Lastly, it illustrates how simple nonlinear models characterized with one circuit can accurately predict distortion levels when the nonlinearity is placed within a very different circuit, showing that knowledge of the interaction gives the ability to accurately predict the behavior of PIM-producing components in a variety of circuits such as resonators, filters, and matching networks.