Using S-parameters for Calibration of Deployed Cables on NIF

The goal of this paper is to outline the process for characterizing the S-parameters of passive two-port electrical devices to calculate the input signal from a measured output signal when standard two-port VNA measurements are not possible. For long cables such as those used at NIF to transmit analog electrical signals long distances from target diagnostics to their respective data digitizer, standard two-port VNA measurements cannot be used to determine the cables’ transfer functions due to the large physical separations between the ports of the cables. Traditionally, this problem was addressed by recording input and output waveforms with two oscilloscopes and then comparing their spectral composition. A new method is to take reflection measurements at one port and substitute three known loads at the other port to generate a system of simultaneous equations that will allow for S21 to be quantified.