Reminder of S parameters
Large signal S parameters for nonlinear device characterisation

Scattering parameters (S-parameters) are undoubtedly one of the most important tools in the design, construction and characterization of microwave devices. S-parameters can be measured simply using a vector network analyzer (VNA). When the latter is rigorously calibrated, the measured S-parameters represent the intrinsic properties of the device, independent of the VNA used to characterize it. Indeed, thanks to calibration procedures, it is possible to eliminate systematic errors due to the VNA and extract all the parameters that determine the device's behavior, such as gain, losses and reflection factor, independently of the measurement system.