The answer depends on the definition of S-matrix. In transmision lines theory usually it is assumed that we operate with single-mode S-matrix which is loaded with transmision lines (50 Ohms) at the ends.elektr0 said:embedded transmission lines (microstrip and coplanar waveguides)
in general have complex characteristic impedances Z, due to losses.
Is there any need to express the scattering matrix of such "complex lines"
with complex reference impedances, or can we still use the Touchstone
export file for real reference impedance.
No. It means that you will include between your lossy transmision lines additional one without losses. That is not corect and will cause non-existent reflections.Is it possible to normalize each s-matrix in a cascade to an arbitrary real reference impedance without loosing information, even if we have to do with complex in and output impedances.
The remedy is to use "power" definition of Z = P/(I^2) whererautio said:The problem with most EM analysis data is that a line integral of E-field (or some other equivalent calculation) results in only an approximate value for Zo. (If you don't like the value of Zo you get, just change the line integral until you are happy.)
Thanks for the article. Ok, I'm EM-guy, that means I always try to think in terms of EM-fields component. So, attempt to describe the discontinuity in nonphysical, imho.elektr0 said:Lets say, we characterized a discontinuity in a microstrip line with strip width 50 microns. After deembedding and renormalizing to a different impedance, we hope to get the characteristic of the same discontinuity but embededded in microstrips with another strip width x=?. RIGHT or NONSENSE ?
What do you mean under "power waves" ? Waves (or modes) are defined only by port boundary conditions and it doesn't matter what kind of Z definition you use.Wiley said:Since power waves do not satisfy the wave equation, deembedding is not the simple pre- and post- multiply by the phase change
Again generalized s-matrix doesn't depend on any impedance def because it is simply unnormalized (!)Wiley said:Waveguide modes in cutoff do no transmit power; hence, power based S parameters for these modes do not exist
elektr0 said:If we simulate the same discontinuity in two different complex line environments.
elektr0 said:@ Wiley
Why are scattering parameters, referenced to complexe impedance necessary in your opinion ?
elektr0 said:I think you didnt get my last question.
I am not sure if RENORMALIZATION is applicable to nonTEM guided wave applications. If we simulate the same discontinuity in two different complex line environments. For example a PCB-Via with strip width 50 um and strip width 150 um. If we RENORM the results from calculation 1. Is it possible to get the results from calculation 2 ???
navuho said:What do you mean under "power waves" ? Waves (or modes) are defined only by port boundary conditions and it doesn't matter what kind of Z definition you use.Wiley said:Since power waves do not satisfy the wave equation, deembedding is not the simple pre- and post- multiply by the phase change
Morevover, deembeding is not applicable at all in a case of lossy media.
Again generalized s-matrix doesn't depend on any impedance def because it is simply unnormalized (!)Wiley said:Waveguide modes in cutoff do no transmit power; hence, power based S parameters for these modes do not exist
It just reflects the fact of signal (amplitude) trasmission between ports and modes. Waveguide below cutoff is an ideal attenuator in that case.
Wiley wrote
If we continue with your example: At a discontinuity higher order modes are excited, so let's add 300 um deembedding lines and place the ports at the end of these lines to make sure these modes have decayed fully. After we obtain the S parameters for the via and deembedding lines, we deembed the S parameters inward 300 um. The deembeding accounts for the phase change and loss introduced by the TEM mode of the deembedding lines. What is left is the via discontinuity and the higher order modes excited by the via coupling to the 50 um line. If you renormalize these S parameters to a 150 um line, the coupling is still to a 50 um. Does this make sense?
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