I. Introduction
Today's high-speed multimedia interfaces, including high-definition multimedia interfaces (HDMI), digital visual interfaces (DVI), unified display interfaces (UDI) and serial advanced technology attachment (SATA) carry two to four differential channels between sources and sinks. There is a common requirement to be able to characterize these channels using a vector network analyzer (VNA) that has a smaller number of measurement ports. For example, HDMI cables and connectors accommodate four high-speed differential channels, while a four-port VNA has become popular in recent years. Since the transformation of 2-port single-ended scattering parameters (-parameters) into differential -port -parameters is straightforward [1], it returns to the old subject of characterizing an -port device with a two-port VNA.