Simulation of S-Parameter-Matrix with complex Port Impedances

[Jan]

Hi,

I noticed some unexpected results, when I did some S-Parameter Simulation with complex Port Impedances. While I am aware, that this is a highly unusual scenario, from a theoretical point of view it is well layed out. From what I can tell from the technical documentation, the S-Parameters in QucsStudio are based on the Power Wave Defintion from Kurokowa (IEEE Paper “Power Waves and the Scattering Matrix” 1965)  which is the usual case and includes complex port impedances. On the contrary, the QucsStudio S-Parameter Simulation seems to ignore the imaginary part of a complex port impedance and to deliver the result for the purley real port impedance case.

I compared it to ADS and AWR. A trivial case as an example is attached.

Btw, the technical documentation is a very nice read. Thumbs up 🙂

Best regards,

Jan

Attachments:

1. 

   Generalized_S_Parameters_QucsStudio_vs_ADS.pdf
   

[QucsStudio]

Hello,

You’re right, complex port impedances are not supported. A warning would be nice here.

But the Touchstone file component supports the necessary transformation, if the property “func” is set to “complexZ0”. For frequency-independent port impedances, the s1p-file needs two lines only. See example in the picture.

<picture removed because of bug>

• This reply was modified 5 months, 1 week ago by QucsStudio.

[Jan]

Thanks a lot!

[QucsStudio]

I just got the hint that there was a bug in the picture above (wrong connection of SnP component). Therefore, I removed it.

Here is the correct schematic for complex port impedances in s-parameter simulations. Note that port 2 of the file component X1 must be connected to the s-parameter source P1.

By the way, this concept gives correct results for noise figure NF and NFmin, but not for optimum source impedance Sopt.

[Author]

Posts