plotting Smith charts

I did some more experimenting and consulting with colleagues, and at this point I'm pretty sure the Smith chart option always shows the scattering parameters, regardless of whether I choose Z-smith or Y-smith.  I'm ultimately interested in getting the normalized complex port impedance... can this be done without resorting to manual transformation from scattering parameters to impedance?

Dear dzakharian,

dzakharian said:

I'm ultimately interested in getting the normalized complex port impedance... can this be done without resorting to manual transformation from scattering parameters to impedance?

I'm not sure if you tried the technique described in the following URL:

https://support.cadence.com/apex/ArticleAttachmentPortal?id=a1O0V00000911gRUAQ&pageName=ArticleContent

Basically, this technique relies on a short ocean script to execute following the completion of your S parameter simulation. It is an extra step, but would prevent you from needing to do a transformation of your output S-parameters to complex impedance. Perhaps you have already tried this - in which case I apologize for my forum post!

Shawn

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

Hi Shawn,

Thanks for the reply.  I'll give that ocean script a shot, but I believe that it still plots the scattering data, not the complex impedances (at least there is nothing in that script that would do the conversion).

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). 

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.

It is also there.

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.

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.

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?