Scattering parameters (S-parameters) are measured with the vector network analyzer (VNA). The correct evaluation of the measurement uncertainties of S-parameters is challenging because the measurand is complex, the measurement model is complex and the quantity of measurement data is usually relatively large. METAS has a pioneering role in the field of uncertainty calculation of S-parameters thanks to pioneering work which takes into account the influence of connectors and the effects of their geometric details. In addition, METAS has made a decisive contribution to the document "Guidelines on the Evaluation of Vector Network Analyzers" (EURAMET Calibration Guide No. 12), which, among other things, is dedicated to uncertainty calculation.
VNA Tools, developed by METAS, is the leading metrology software for the VNA. It calculates S-parameter uncertainties according to internationally recognized guidelines (GUM). VNA Tools runs as a stand-alone software on a PC and supports all major VNA brands. It imports the raw data from the VNA and performs all calculations externally. The program is very modular and flexible and its use requires a high degree of expertise and knowledge. The software is mainly used by national metrology institutes and some of the more advanced calibration laboratories.
VNA manufacturers are interested in making the task of VNA uncertainty evaluation even easier. They want to calculate and display the measurement uncertainties directly on the VNA. This should make the correct VNA measurement uncertainty evaluation accessible to a larger community of VNA users.
The VNA Tools Real Time Interface (RTI) was developed with this idea in an earlier project (F-5217.30078). It is an interface on a high abstraction level to the functionality of the VNA tools with a guarantee for long-term stability. The RTI is an integral part of the VNA tools, but it is protected by a digital key, and in order to access it, a commercial license must be purchased from METAS. So far two companies use it.
VNA-Tools has been continuously improved since 2011 and new features like RTI have been added. This project aims to further develop VNA tools and the RTI interface by implementing support for wave parameters for linear and frequency-converting instruments, thus supporting nonlinear measurements. METAS will first extend VNA tools with this functionality and then extend RTI accordingly.
