Comments by Jean-Roger, Nizar and others concerning accuracy of S11 shunt measurements inspired me to write this post.
The accuracy of any measurement is important and an excellent paper on this subject was
written by Brian Walker of Copper Mountain Technologies (a VNA manufacturer).
"Make Accurate Impedance Measurements Using a VNA" available from
This paper has been discussed on groups.io before and has been subject to misinterpretation
by myself and others. So I contacted the author and he was kind enough to answer my
questions and send me his spreadsheet for error analysis. The paper goes into considerable depth on how to calculate the impedance measurement and an error equation is derived to calculate ¦¤S11(max).
The author then goes on to derive ¦¤S11 for a Copper Mountain Technologies S5065 VNA which can measure from 9 kHz to 6.5 GHz with a reflection accuracy (S11) specified to be ¡À0.4 dB for measurements from ?15 to 0 dB. The curves and charts in his article are all based on THIS specification. They are NOT applicable to the NanoVNA which has better performance when used over a much narrower frequency range.
I wrote a technical note that provides more detail on his paper and how it can be applied to the NanoVNA. I hope you find it informative. It can be downloaded from my Box account at the link below"
A summary of the report is as follows:
? The NanoVNA is capable of making accurate measurements of component parameters provided that quality calibration loads and a proper test jig are used.
? Components (resistive and reactive) with an impedance range of approximately 1 to3K can be measured with reasonable accuracy using the 1 port S11 shunt method
? The uncertainty of measuring the S11 reflection coefficient will determine the error to be expected when measuring components.
Roger
Roger Need