On Peculiarities of S-Parameter Measurements

Extracting quantities, such as the propagation factor or the characteristic impedance of a transmission line based on measured S-parameters, can be more involved than expected. Experience teaches that even if the S-parameter measurements look smooth and are of good quality, the derived quantities can contain large spikes that tend to grow when connection imperfections are present. In this paper, the presence of the peaks is shown in practical measurements, a possible explanation for their presence is provided, and a sensitive indicator (the image parameters) for the imperfections is proposed.