Thesis (M.S., Electrical and Computer Engineering)--University of Idaho, June 2015 | Diff erential signaling is an important technique for voltage high-speed digital system to avoid electromagnetic interference. Di fferential networks are characterized using mixed-mode S-parameters that are typically obtained by conversion from single-ended S-parameters or direct measurements. We fou nd that the conversion matrix may affect the conversion accuracy due to ill-conditioning. We study the condition number of the conversion matrix using two test cases: broadside coupled striplines and edge coupled microstrips. We also develop a way to simulate diff erential S-parameters with true excitations and apply it to characterizing the Power Distribution Networks which should not be characterized by single-ended S-parameters due to ground bounce and IR drop. Finally, recently developed causal Fourier continuation is employed to verify the causality of single-ended and mixed-mode S-parameters. In addition, we use a causality argument and the Fourier continuation based method to extract time delay from single-ended S-parameters and then from mixed-mode S-parameters in the future.