White Paper: AWR's Support Of Polyharmonic Distortion And Nonlinear Behavioral Models

Linear and nonlinear device models are the building blocks of most RF and microwave designs. S-parameters are often used to represent linear devices. As a "black-box" model, they can easily be obtained using a vector network analyzer and distributed for simulation. S-parameters use superposition to equate the linear relationship between incident and reflected waves at all of the device's ports. Nonlinear devices, however, distort waveforms such that their behavior cannot be represented through superposition or S-parameters.

Historically, nonlinear devices have been represented in simulation by compact empirical or analytical SPICE models that operate in the time domain. Today's high-frequency circuit simulators analyze the linear portions of the network in the frequency domain and the nonlinear components in the time domain, resolving the two through an iterative technique called harmonic balance.