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Precise measurement of symmetrically transmitted scattering parameters


As part of an industrial cooperation, PTB recently set up a complete measurement uncertainty budget for symmetrically transmitted scattering parameters, the so-called mixed-mode scattering parameters, for the first time. This parameter is particularly relevant for differential line systems, such as those used for printed circuit boards or multi-wire transmission lines.



Due to the pronounced insensitivity to interferers, symmetrical signal transmission (differential signalling) has been used in many applications for a long time. Prominent examples are network connections (LAN) or data buses in computer systems. Also, in the automotive sector, low-loss and interference-insensitive networks become increasingly important because of the constantly increasing signal bandwidths. Since the release of the new edition of "Quality management systems - Particular requirements for the application of ISO 9001:2008 for automotive production and relevant service part organizations, 16949: 2016" by the IATF (International Automotive Task Force) there has also been an increased requirement with regard to metrological traceability (Section This was the motivation for a large international cable manufacturer with almost 100 000 employees in over 100 locations worldwide to initiate and carry out a measurement uncertainty analysis for mixed mode scattering parameters. For this purpose, the industrial enterprise has started a cooperation with PTB in 2018.

The result of this cooperation is a complete measurement uncertainty budget for mixed-mode scattering parameters. The measurement uncertainty contributions include influences of drift, noise, and linearity of the measuring instrument (a vector network analyser, VNA), influences of cable movement, contributions from calibration standards, and include measurement repeatability and the influence of the measuring adapter. Since only the properties of a transmission line were to be measured, but no standardised connections for this measurement object did exist, the focus of the investigation was primarily on the influence of the measurement adapter.


Line arrangement of the twisted pair cable and measured transmission of mixed mode scattering parameters

Figure: Line arrangement of the twisted pair cable (top panel, source: commons.wikimedia.org/w/index.php) and measured transmission of mixed mode scattering parameters up to 3 GHz (bottom panels). Semi-transparent areas in the graph on the right-hand side represent the expanded measurement uncertainty.



Department 2.2 “High Frequency and Electromagnetic Fields”