What is meant by: “Short�? calibration of the coil and conversion to “Z: Reflection�??

[Ted Jackson]

In application note AN4974

https://www.st.com/content/ccc/resource/technical/document/application_note/group0/94/99/80/37/c8/08/46/7f/DM00347152/files/DM00347152.pdf/jcr:content/translations/en.DM00347152.pdf

Section 7.3 - Verification of the Q factor in the frequency domain (page 40)

Line 4 is a bit ambiguous:

4. "Short" calibration of the coil and conversion to "Z: Reflection"

Can anyone tell me what is being said there a bit more clearly, please? I'm familiar with the open/short/50ohm calibration procedure of the VNA and some aspects of Smith charts. But that line stumps me.

[nmeunier]

Hello Travis,

I also have trouble measuring the Q factor of an antenna with a MiniVNA Pro. In your last message, you provide 2 screenshots for which I would like some precisions :

• The first one is, according to the display, S22. So when does the conversion to Z:Reflection mentioned in the AN4974 steps in ? I also assume that S22 is equivalent to S11 in your setup, is it true ?
• The second one is the Return Loss which is related to the S11. You advise to convert it to Z-parameter, but to do so you need S21, S12 and S22 (see formula below).

 

This last point on S21 is true for both. According to the Agilent E5061A/E5062A ENA Series RF Network Analyzers User’s Guide, Zreflection is a function of Sab (see image below), which is S21 to me.

My question is : did you perform a transmission measure ? How ?

Finally, isn't the measure of Q on time domain with a scope more precise ?

Thanks for your answers,

Nicolas Meunier.

[Travis Palmer]

Hello Nicolas,

Yes the conversion with the above formula is do able. Anyhow our VNA has a build in conversion function which does the job.

Yes Chapter 7.2 of the above mentioned application note AN4974 guides you, how to calculate the q-factor from rise and fall time between 90% and 5% of the signal.

BR Travis