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Coupled transmission line

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hmsheng

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Who can give a coupled transmission line model?
The coupled line consists of two strip with 4 port. 4-Port S-parameter file is given by EM simulation. How can I extract the coupled capacitance of the two strips?

Thanks.
 

Manjunatha_hv

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Hi hmsheng,


which circuit or EM simulator you are using (Microwave Office or Sonnet)?
Do you want spice or S parameter file?
 

hmsheng

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The EM simulation is done with Momentum.
And Spice model is wanted.
 

eckypting

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hmsheng said:
Who can give a coupled transmission line model?
The coupled line consists of two strip with 4 port. 4-Port S-parameter file is given by EM simulation. How can I extract the coupled capacitance of the two strips?

Thanks.

See the attached application notes & article for a discussion of converting 4-port "mixed mode" S-parameters to 2-port "single-ended" S-parameters. Also, you may be interested in the references noted at the end of these articles, as well.

Alternately, you can get the App Notes via these links:

https://pdfserv.maxim-ic.com/en/an/4hfan510.pdf

https://www.si-list.org/files/tech_files/Understandmm.pdf

Ansoft Designer, which is what I use these days, has a built-in (but poorly documented) capability for converting differential lines into singled ended lines by making one port (created as a "page port", not an RF port) the reference for another. I don't know how @DS deals with it, however.

Cheers,
eckypting
 

hmsheng

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eckypting:

It's helpful. Thanks.
Can you also provide a equivalent circuit for coupled transmission line?

Best regards
 

woshifanka

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dear all .
i have a question ? how to set a impedance match in antenna design in HFSS ?
 

rautio

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For an equivalent circuit, analyze the coupled line in SonnetLite (free download www.sonnetsoftware.com, I work for Sonnet) with ports 1 and 2 on one side, ports 3 and 4 on the other, both numbered from top down. Set reference planes so you have one or two cell long transmission line (i.e., very short length). Make sure the total line length is at least twice the substrate thickness. After you get S-parameters, display a graph of the data.

Now, with the graph displayed, go to the Output menu (at the top). One of the options is to output R, L, C, and G parameters of a coupled line. These are per unit length, where the unit length is the de-embedded length of transmission line you analyzed. This model can be used in various versions of SPICE. There will be one model for each frequency you analyzed. Check validity of the model by making sure the models change very little from one frequency to the next

You could also do this in Momentum and export S-parameters. Then load them into the Sonnet graphing program and again go to the Ouptut menu. However, customers comment that when they do this with Momentum data, the model varies a lot with frequency and the problem appears to be due to small errors introduced by their de-embedding. (This sort of model extraction is very sensitive to small errors.) My guess is that it is because without a perfectly conducting sidewall, they do not have an exact ground reference for the ports. Several unsuccessful attempts have been made by these customers to get full technical details of the Momentum de-embedding. If anyone knows where Momentum de-embedding might have published details, please let me know. (Sonnet de-embedding was completely detailed many years ago, but also in the most recent MTT Trans.)

To get odd mode, in Sonnet make the input ports 1 and -1, output ports 2, +2. For even mode, make both input ports 1, and both output ports 2. Even and odd mode impedances come directly out of the Sonnet de-embedding, or you can take the RLCG model and use Z = sqrt( (r+jwL)/(g+jwC) )...this works fine unless you don't happen to believe in complex Zo (in this case, please see your minister). Also, this will be off by a factor of 2, don't remember which way, but it is in the manual included with SonnetLite.
 

hmsheng

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Thank rautio!

I can only get LCT spice model for coupled line. But @DS can't import such netlist format. So can I output in Pspice format? Or how can I use LCT spice format model?

By the way, following is a LCT spice model for coupled line. I don't know how to read this netlist. Can you give some help? And can we draw an equivilent LRCG circuit from this netlist?

----------------------------------------------------------
* Spice Data
.y1 1 3 2 4 0 ymod l=1.0
* Analysis frequency: 2000 MHz
* *****Place terminations after this line.*****
.model ymod tra nlines=2
+ lmatrix=0.030502n,0.091791n,0.030502n
+ rmatrix=0.595465,0.004591,0.595465
+ cmatrix=0.005015p,-5.44e-3p,0.005015p
+ gmatrix=3.719e-6,1.731e-6,3.719e-6
----------------------------------------------------------

Best regards,
HMSheng
 

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