Electronics > RF, Microwave, Ham Radio

S-Parameter plotting software

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joeqsmith:
AppCAD is a simple RF calculator which includes a Touchstone plotting feature.  Sadly the software appeared to change hands from Agilent to Avago Technologies (now Broadcom) and has not been updated since 2012. 

https://www.broadcom.com/appcad

It has a few limitations and I wonder if there are better tools available.   Google search hasn't helped yet:

https://www.rfpage.com/free-tools-to-analyze-and-plot-s-parameters-file/

Is anyone aware of a Windows 10 compatible viewer that will allow you to overlay 5 or more Touchstone files with different ranges, sample sizes and variable frequency steps?   

rf-messkopf:
You may want to take a look at the METAS VNA Tools by the Swiss national metrological institute:

https://www.metas.ch/metas/en/home/fabe/hochfrequenz/vna-tools.html.

You have to register if you want the full version, but there is also a reduced one (VNA Data Explorer) free to download, which only contains the data plotter. The full version adds a lot of functions like offline calibration and S-parameter uncertainty evaluation according to the EURAMET calibration guide.

As a data plotter the VNA Tools are very convenient and hard to beat in terms of speed and versatility. They are ideal if you quickly want to look at different Touchstone files and make comparisons, etc. You can pot linear/logarithmic magnitude, phase, convert to Z-parameters, plot in one or several diagrams, take differences and quotients, do time domain analysis, calculate passivity and switch terms, etc. The user interface is a bit unusual, but actually very powerful, especially with the integrated file manager. The only lacking feature is a Smith chart plotting facility. You can however plot \$S_{nn}\$-data as a polar plot with rectilinear coordinates, but not with the curved Smith coordinate lines. For me this is not a real shortcoming as long as I only want to look at S-parameter data.

As was already mentioned, the most flexible option would be a math package like MATLAB, Octave, Python (scikit-rf) with good plotting capabilities. Then you can do arbitrary math on the data, the plots are infinitely customizable, and can be output in publication quality in any format you want. Takes longer to set up, though.

A third option is to use a simulation package with S-parameter simulation capability. I often use QucsStudio, which is free and very powerful: http://qucsstudio.de/de/start/. Besides plotting this allows to add circuit elements to your S-parameter data. Also takes longer to set up and is not too convenient for browsing files real quick.

joeqsmith:
Thank you both very much.  I would like to avoid creating a viewer.         

I have downloaded the free METAS viewer and installed it.   I have also filled out the registration but doubt that will happen today.  It's much nicer than the AppCAD viewer.  Just selecting the files to load was a real pain in AppCAD. 

It works great with the basic files.  Very fast and user friendly.   The first thing I noticed is that the screen will flicker at random every 1-10 seconds.  It will do this with no files selected.  It appears it is rescaning the drive and refreshing the file list.  Is this normal?

rf-messkopf:

--- Quote from: joeqsmith on July 04, 2021, 05:59:35 pm ---It works great with the basic files.  Very fast and user friendly.   The first thing I noticed is that the screen will flicker at random every 1-10 seconds.  It will do this with no files selected.  It appears it is rescaning the drive and refreshing the file list.  Is this normal?

--- End quote ---

No such flickering on my machine with the full version.

They have set up a user forum for METAS VNA Tools at https://groups.google.com/g/vnatools. Perhaps it is a good idea to post there and report that problem.

joeqsmith:
The flicker will continue even if the software looses focus (not currently selected).   

Now that I know it works well with typical good files I'll try something more difficult. 

In this first test, I have used my software to sweep the NanoVNA (nothing attached) from 10kHz to 1MHz with a 10kHz segments.   There's a bit or a rounding error which throws AppCAD into a tizzy, but METAS seems to handle it just fine.

****
To be clear, when I say rounding error, the frequencies I use are off a slight amount making the spacing between samples uneven. 

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