S2p Touchstone import CST MWstudio

[Andrew77]

Hi,
importing a S2p touchstone file (a two port element defined in its S- Paramenters)in CST (in 2 point lumped elements) doesn't work because I have to add a reference ground

How can I add a reference ground?
thanks
Andrea

 

[BigBoss]

That EM structure must have a reference either Global Ground Layer or Enclosure Ground.
This floating element can not be represented by 2-Port s-parameters.

 

[volker@muehlhaus]

If the S2P has no shunt elements, you could first convert it to S1P using circuit simulation, with a single floating port across input and output.

 

[Andrew77]

If the S2P has no shunt elements, you could first convert it to S1P using circuit simulation, with a single floating port across input and output.


View attachment 192901

Thanks, sounds interesting, but so, to get the two port, Do I split to S11 and S22, and connect the S11 to the left ustripline and the S22 to the right of the ustripline? How I get the Two Port S2p?

 

[volker@muehlhaus]

Thanks, sounds interesting, but so, to get the two port, Do I split to S11 and S22, and connect the S11 to the left ustripline and the S22 to the right of the ustripline? How I get the Two Port S2p?

I am afraid you misunderstood the concept. Using S11 on one side and S22 on the other side is wrong.

Think of your S2P block as a PI element, with series and shunt path.

If you convert to S1P using the method that I showed, you get the impedance between terminals 1 and 2 of the S2P block, with floating ground node. Using this 1-port data is a valid approach as long as the shunt elements in the S2P are not (very) important. For example if your S2P is SMD component data, you can use this method. You then use the resulting S1P from circuit simulation in the CST model that you showed above.

So all you need is some circuit simulator where you can wire the S2P in the way that I showed above, with the circuit simulation port connected across the data block, between port 1 and 2 of the S2P block. Note that the circuit simulator block is NOT connected to S2P ground!

~~

That said, the more accurate method is to use an EM tool where you can properly define two ports to insert the S2P data. In your case, that would be one EM port from the left trace to common ground, and another EM port from the right trace to common ground. So you need a common ground in your model, and for accurate results it would be useful to have port calibration. CST does not support that, so for PCB work with SMD components a planar EM tool like ADS Momentum or Sonnet is the more accurate solution.