Matching network characterisation by S-parameter measurements of two-part active devices

A method for characterising two-port matching networks at the input and output ports of a GaAs MESFET at a single frequency is described. Two steps are involved. First, measurement of the input reflection coefficient of the overall circuit with the transistor drain voltage equal to zero and for different values of the gate voltage. Secondly, S-parameter measurements of the overall circuit for two sets of transistor drain and gate bias voltages. Equations are presented which make possible the calculation of S-parameters of the passive matching networks from these measurements, provided that the transistor S-parameters are known for each of the bias points.