Incorrect sourceimpedance when using S1P block with measured impeedance.

[Andy_JP]

I need to perform an inter-stage matching. So I measured COMPLEX and Frequendy Dependent impedances at the power of interest with R&S VNA, and recorded S1P files.

But when connecting the S1P block to standard 50 Ohm (real-impedance only) simulation port, with the “Ref” pin to GND, or the return bus for the floating receiver circuit.

After that, on the other side I see some gibberish, not the Impedance I have measured.

Earlier I have discussed that with Michael by E-mail, and he suggested a “correct” schematic, as he sees it. But it did not work with the same result. He did not respond then, and the registration at the forum was closed.

Now the registration is open, and I allowed yself to post it as a bug report here.

 

Note the attached images. I tried both. One is the reference from http://qucsstudio.de/forums/topic/simulation-of-s-parameter-matrix-with-complex-port-impedances/
another is my approach to the floating circuit with isolated ports. maybe I should have connected ref to the port negative pin, I don’t know.

It just did not work.

• This topic was modified 4 months, 2 weeks ago by Andy_JP.
• This topic was modified 4 months, 2 weeks ago by Andy_JP.
• This topic was modified 4 months, 2 weeks ago by Andy_JP. Reason: typos

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[Carsten]

Hi Andy,

I don’t understand this sentence:

>But when connecting the S1P block to standard 50 Ohm (real-impedance only) simulation port, with the “Ref” pin to GND, >or the return bus for the floating receiver circuit.

I expected a structure like “But when …, then…”.

Also, what do you mean with “floating receiver circuit”?

Maybe you want to correct your forum post?

Mind, that you acquired a s1p file, but are using a 2-port-symbol. It would not surprise me, that this gives random results. You can edit the number of ports in that block’s properties.

Best

Carsten

 

[Carsten]

>Mind, that you acquired a s1p file, but are using a 2-port-symbol.
>It would not surprise me, that this gives random results. You can edit the number of ports in that block’s properties.

I saw the other forum post. That is seemingly needed, if you have complex port impedances.
Still, I don’t see how this is needed in your case.

PS: I could not edit my last post. Seemingly the edit button is sometimes shown and sometimes not.

[Andy_JP]

There obviously was a comma, which I separated for your ease, and forgot to clear “but”, but lets not discuss stylistics, because everything is told in the next sentence.

The floating circuit is floating in the air and does not nave any ground potential explicitly defined, or has a reactance in the return path in other words. I think, that is obvious, since you cannot simulate truly floating potential (like unconnected pins) without introducing some stochastic environment model. 

The Ground potential is defined at the other side of the circuit, at the port-2.

But as you see, I tried simulating with fixed GND potentials at both ports, it did not change anything.

 

>Mind, that you acquired a s1p file, but are using a 2-port-symbol

That is a feature of S1P-block. Follow the refrence. With “ComplexZ0″ function it converts the fixed impedance port, into the measured S1P impedance. <span style=”text-decoration: underline;”>I.e. it should, but it does not because of some bug.</span>

> That is seemingly needed, if you have complex port impedances.

That is exactly what I have – complex frequency dependant port jmpedances. Technically, CST and ADS solve this problem without efforts. And “ComplexZ0” function should do the same.

• This reply was modified 4 months, 1 week ago by Andy_JP.

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