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plotting Smith charts

Hello,

I'm running an .sp analysis with a simple setup--port set to 100ohm, with 100ohm load. I'm plotting results on a Z-Smith, which i thought should give me Re(Z)=1 (normalized)... but instead I'm getting something like 2e-12 as the prime center. I don't understand why this is the case. I'm relatively new to Smith charts, but I'm guessing the plot actually shows reflection coefficient, not the impedance? If this is the case, how can I request an impedance plot?

I'm on version 6.1.8.

Many thanks in advance for your help,
David

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ZoltanT over 5 years ago

Hi dzakharian,

It seems good to me. You have a 100 Ohm reference system loaded with 100 Ohm. No reflection, so S11=0. The 2p is probably numerical error. 2e-15 is very good accuracy!

The Z- and Y-Smiths returns the same reflection coefficient plane, just with different grids. Clearly this is not how one works with Smith charts on paper, but once the server does all the calculations it is great, or even better.

Regards,
Zoltan
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dzakharian over 5 years ago in reply to ZoltanT

Hi Zoltan,

Yes, the matching at S11=0 is perfect, in terms of scattering parameters. But I'm interested in the actual impedance, not scattering parameters (so Z11, not S11).
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Andrew Beckett over 5 years ago in reply to dzakharian

Why not plot Z11 then? You could plot zpm('sp 1 1) on a polar chart (not sure it makes much sense to plot Z11 on a Smith Chart, but I'm not a microwave engineer so I might be talking rubbish). You can also plot real(zpm('sp 1 1)) and imag(zpm('sp 1 1)) on a rectangular graph to see the complex impedance that way. Or plot one versus the other with waveVsWave.

Andrew.
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ZoltanT over 5 years ago in reply to dzakharian

It is also there.
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ZoltanT over 5 years ago in reply to Andrew Beckett

Andrew, a stereotypical typical microwave engineer is more likely to think in terms of normalized waves, than fuddling with impedances or dealing with the differences between a current or voltage signal.
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dzakharian over 5 years ago in reply to Andrew Beckett

Hi Andrew,

Thanks for the tip. I'm not a microwave engineer, but am learning how to design a matching network, so I was looking to get some insight into what happens to the impedance as I vary parameters, as opposed to scattering params. Z11 on polar chart worked, but I was wondering if there is a way to specify a "chart type" in Assembler output? Right now I have zpm('sp 1 1) as my expression, but when I plot it always defaults to smith chart "impedance" graph.
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dzakharian over 5 years ago in reply to ZoltanT

Hi Zoltan,

Thanks for pointing this out! Exactly what I wanted. Do you know if there is a way to extract Z and Y values in the Tracking Info using calculator functions?
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Andrew Beckett over 5 years ago in reply to dzakharian

In IC618 you can arrange the graphs the way you want and then save it as a plotting template. That's the way to define the type and style of your plots - we decided against having a gazillion options to control how you want something plotted automatically.

Andrew.
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ZoltanT over 5 years ago in reply to dzakharian

I do not know. I am just a simple user, but I would look for it in ViVA's skill reference first, or wherever the marker syntax is described.
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ZoltanT over 5 years ago in reply to dzakharian

I do not know. I am just a simple user, but I would look for it in ViVA's skill reference first, or wherever the marker syntax is described.
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