Complex characteristic impedance
Dear Microwaves Colleagues,
An issue with complex characteristic impedances
as recently been reported with the
RF Python package scikit-rf
, 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
formulation of the scattering parameters, and not the
formulation. The differences between these two formulations have been discussed since long in the literature (see - for instance for pro-pseudo waves, - for pro power-waves), 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  it is said that when using pseudo-waves with complex-valued reference impedances, the electromagnetic reciprocity condition does not necessarily mean that the scattering matrix is symmetric. But, even complex-valued reference impedances, EDA software like ADS and ANSYS always give symmetric S matrices...
So, my question is, are you aware of EDA softwares implementing
 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.
 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.
 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.
 S. Llorente-Romano, A. Garca-Lampérez, S. H. Yeung, T. K. Sarkar, M. Salazar-Palma, et S. W. Ting, « Characterization of Microwave Circuits: S-Parameters », in Wiley Encyclopedia of Electrical and Electronics Engineering, Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015, p. 1‑18.
For those who may be interested, we have finally decided to stick with power waves definition.
Despite being not correct in some case with complex characteristics impedance, it is the most common implementation and such the most expected results by users.
First of all, quantify your approximation : how much non-real is your caracteristic impedance ? If, for instance, my characteristic impedance is 50 + 0.1j Ohm, I would simply drop the imag part.
Stay in touch,
Sorry for the late reply.
In my applications for instance, the imaginary part is much larger than the real part..
My experience with Microwave Office is that they just throw away the imaginary part of the impedance in transmission line calculations. Sorry I am no help!
Sign in or register to add a comment.
Add a Comment
About Our Site
Biological Effects and Applications
Computer Aided Design
Emerging Applications and Technology
Filters and Passives
MMIC and RFIC
Packaging and Materials
Sources and Receivers
Test and Measurement
Seeking the original reference for a microstrip line impedance formula
Difference between intrinsic and characteristic impedance
Characteristic Impedance of Signal conductor
Impedance Measurement Kit MA414A - Anritsu
Terms of Service
Useful Hints and Tips
Created with PlushForums
© 2023 Microwaves 101 Discussion Board