X-parameters are a generalization of S-parameters and are used for characterizing the amplitudes and relative phase of harmonics generated by nonlinear components under large input power levels.
X-parameters are also referred to as the parameters of the Poly-Harmonic Distortion (PHD) nonlinear behavioral model.
This situation is unlike that at DC, where one can simply add the values of resistors connected in series.
[3] X-parameters were developed and introduced by Keysight Technologies as functionality included in N5242A Nonlinear Vector Network Analyzer,[4][5] and the W2200 Advanced Design System in 2008.
[7] X-parameters are the parameters of the polyharmonic distortion modeling work of Dr. Jan Verspecht[8][9] and Dr. David E.