State-Space Method
S-parameters describe a system in terms of its frequency-dependent responses. The state-space model assumes a linear time-invariant (LTI) system with a vector of inputs u(t) of length P and a vector of outputs y(t) of length Q:
The state-space model represents the data as a vector of N state variables x(t) representing the responses of the system for all inputs in the specified range, and four state-space matrices, A, B, C, and D.