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.