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8th January 2020, 14:36 #1
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Complex characteristic impedance and scattering matrix formulation
Dear Microwaves Colleagues,
An issue with complex characteristic impedances has recently been reported with the RF Python package scikitrf, which has led to many discussions. Maybe people here would have interesting advices or comments about that problem, which is the following.
Most EDA softwares, such like ADS or ANSYS Circuit implement powerwave formulation of the scattering parameters, and not the pseudowave formulation. The differences between these two formulations have been discussed since long in the literature (see [1][2] for instance for propseudo waves, [3][4] for pro powerwaves), each having advantages and inconveniences. However, when characteristic impedance are real valued, there is no difference between these two formulations.
However, when the characteristic impedances are complex valued, differences should appear. In particular, from ref [1] it is said that when using pseudowaves with complexvalued reference impedances, the electromagnetic reciprocity condition does not necessarily mean that the scattering matrix is symmetric. But, even complexvalued reference impedances, EDA software like ADS and ANSYS always give symmetric S matrices...
So, my question is, are you aware of EDA softwares implementing pseudowave formulation?
[1] R. B. Marks et D. F. Williams, « A general waveguide circuit theory », J. RES. NATL. INST. STAN., vol. 97, nᵒ 5, p. 533, sept. 1992, doi: 10/gf3wcs.
[2] D. Williams, « Traveling Waves and Power Waves: Building a Solid Foundation for Microwave Circuit Theory », IEEE Microwave Magazine, vol. 14, nᵒ 7, p. 38‑45, nov. 2013, doi: 10/ggc2zn.
[3] J. Rahola, « Power Waves and Conjugate Matching », IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 55, nᵒ 1, p. 92‑96, janv. 2008, doi: 10/fgnf7j.
[4] S. LlorenteRomano, A. GarcaLampérez, S. H. Yeung, T. K. Sarkar, M. SalazarPalma, et S. W. Ting, « Characterization of Microwave Circuits: SParameters », in Wiley Encyclopedia of Electrical and Electronics Engineering, Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015, p. 1‑18.

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19th February 2020, 08:42 #2
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Re: Complex characteristic impedance and scattering matrix formulation
Nobody ? ;(
Finally, we have chosen to stick with Power Waves definition, since most users are waiting for such results...

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19th February 2020, 10:22 #3
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Re: Complex characteristic impedance and scattering matrix formulation

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19th February 2020, 19:49 #4
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Re: Complex characteristic impedance and scattering matrix formulation
Thanks, I'm aware of this thread, which I saw before posting this one.
But that does not answer my main question: are you aware of EDA softwares implementing pseudowave formulation?
Both ADS and ANSYS Circuit uses PowerWaves definitions. In order to compare PseudoWave implementation in scikitrf package, I need to compare with results obtained with such a definition.

20th February 2020, 01:42 #5
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Re: Complex characteristic impedance and scattering matrix formulation
See attached figure in https://www.edaboard.com/showthread....ching/page2#26
Keysight ADSsim and Momentum : PowerWave Formulation
Keysight EMPro : PseudoWave Formulation

20th February 2020, 07:59 #6
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Re: Complex characteristic impedance and scattering matrix formulation
Thanks. Do you, or someone here, have this software?
I would be interested in the following test : let's assume a 2 port network of Sparameters (defined for 50 ohm reference impedance) at 75.8 GHz
Code:[[0.194  0.228j, 0.721 + 0.160j], [0.721 + 0.160j, +0.071  0.204j]]
Code:z_ref = 100 + 10j

20th February 2020, 14:22 #7
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Re: Complex characteristic impedance and scattering matrix formulation
See https://www.edaboard.com/showthread.php?347861#17
There is no practical value to study SParameters for complex reference impedance.
1 members found this post helpful.

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20th February 2020, 17:30 #8
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Re: Complex characteristic impedance and scattering matrix formulation
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