High Quality Content by WIKIPEDIA articles! X-parameters are a mathematical superset of S-parameters and are used for characterizing the amplitudes & relative phase of harmonics generated by nonlinear components under large input power levels. X-parameters represent a new category of nonlinear network parameters for high-frequency design and were developed and introduced by Agilent Technologies as functionality included in N5242 Nonlinear Vector Network Analyzer, and the W2200 Advanced Design System in 2008. (Nonlinear vector network analyzers are sometimes called large signal network analyzers.) X-parameters are applicable to both large-signal and small-signal conditions, for linear and nonlinear components. THey are a mathematical superset of S-parameters meaning that, in the limit of a small signal, Agilent s X-parameters reduce to S-parameters.