Calibration
How to build confidence in
VNA test and measurement Ever-higher operating frequencies for components and devices have led to something of a crisis of confidence in their test and measurement veracity. Fortunately, as Rohde & Schwarz UK product manager Jamie Lunn explains, new solutions giving a trustworthy calibration along with verification standards are now available to provide a higher level of assurance for designers, manufacturers and their customers.
years. Some users are highly experienced. They have extensive knowledge of measurement techniques, and the know-how to apply it to specialised devices and components. Others blindly follow a predefined procedure to extract the wanted measurement results. Whatever the level of expertise, getting good results typically relies on a network analyser and a calibration kit, which are periodically calibrated every 12 months by the equipment manufacturer or an accredited laboratory.
T
So, What ExactLy IS thE PRobLEm? The first issue is that a year is a long time in the electronic component and devices world. In a very short time, just a small change in the measurement setup or environment can have huge unwanted effects - and overall the dependability of the results are influenced by many factors. Uncertainties can snowball with the addition of different test port cables and adaptors. Then there is measurement drift due to temperature changes, not to mention the wear and tear of the calibration standards. Last
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hroughout industry, users of vector network analysers have been able to provide reliable measurements for many
but not least, data sheets only give numbers derived under specific conditions - variables have a greater effect on performance as measurement settings are often different to those in the data sheet. Often these are not applicable to real-life test conditions. This is particularly relevant to higher-frequency environments. For example, the move from the sub 2.5 GHz 3G / 4G wireless networks up to 5G equipment using the higher FR2 frequency bands (in the region of 25 GHz to 50 GHz) means that parasitic effects, mismatches and other variables, have a more-than-incremental impact on system performance. It is easy to lose sight of such counsels of
perfection. For many people on the test and measurement front line, there is little incentive to give full attention to these factors: no consideration for the effect on the overall measurement accuracy. The assumption is: that the instrument is accurate, the displayed results are correct and consistent, so their device must be meeting its specification.
mEaSUREmEnt accURacy Whether they are aware or not, test engineers are not the cause of the problem. Management, sales and their customers have the headache
The ZN-Z229 calibration kit
that not knowing the overall measurement accuracy can reduce the quality of the device being measured. If there is no way to guarantee their accuracy and reproducibility, the numbers being given may be meaningless without reliable uncertainty information. On the other hand, knowing the measurement
uncertainty and hence how close the measurements are to the specification limit may help to improve overall yield and save money on expensive rework. Furthermore, properly calculated error bars can aid compliance to quality control standards like ISO 9000. A further consideration is the cost penalty of delivering hardware that does not meet the
March 2021 Instrumentation Monthly
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