Commissioning of a VNA dynamic uncertainty tool for microwave S-parameter measurements

Abstract

All measurements have an associated uncertainty and it is important to know the uncertainty in order to quantify the reliability of the measurement result. At the National Physical Laboratory (NPL), the provision of scattering parameter (S-parameter) measurements at microwave frequencies for customers is achieved using the Primary Impedance Microwave Measurement System (PIMMS). PIMMS also evaluates the uncertainty in the measurements. The use of PIMMS can be quite onerous as several repeat calibrations and measurements are required to evaluate the measurement uncertainty, which is calculated during post processing of the measured data. The Vector Network Analyser Dynamic Uncertainty Option (VNA-DUO) is available on PNA and PNA X network analysers from Keysight Technologies and enables the real time display of S-parameter measurements and the associated measurement uncertainty. The uncertainties are calculated within the VNA and are displayed on the screen as error bars in real time. This report describes the commissioning of VNA-DUO at NPL by measuring the S-parameters of several one- and two-port devices using both VNA-DUO and PIMMS, and the results from the two methods are compared. The report discusses the components of uncertainty that contribute to the overall uncertainty in the S-parameter measurements made using VNA-DUO and investigates the influence of each component on the overall uncertainty. Thru Reflect Line (TRL) calibration, Short Open Load Reciprocal (SOLR) calibration and an Electronic Calibration (ECal) module have been used for the VNA-DUO measurements. TRL calibration was used for the PIMMS measurements. The investigation was carried out in 3.5 mm coaxial line over the frequency range 100 MHz to 26 GHz. To obtain a wide range of measurement values, one-port devices with very low to very high return loss and two-port devices with very low to very high insertion loss have been used.