Spectral linearization
Large signal S parameters for nonlinear device characterisation

The concept used here applies to the steady-state behavior of time-invariant nonlinear components with incoming and outgoing waves distributed over a list of harmonic frequencies or spectral map. This generalized formalism necessarily entails a high degree of complexity. Each spectral map is a non-linear function of each DC bias condition and of all the amplitudes and phases of each spectral component of each signal applied to each port. Retranscribing such behavior in all variables for a considerable number of ports and harmonics would be prohibitive in terms of data acquisition and model simulation time and memory size.

In practice, only a few strong signal components need to be taken into account without loss of generality, and the other spectral components can be considered small and treated by a perturbation method.