Working with HyperLynx PI, I have found an issue when I tried to make a PDN analysis of my design making use of S-Parameter models for the capacitors.

To reduce the explanation, I'm going to reduce the circuit to a single capacitor, but actually I facing the problem in an anlysis of the complete PCB's PDN.

Then, analyzing a single 470nF ceramic capacitor, I get the right response, no matter whether I work with RLC or S-Parameter model.

You can see it at below picture.

- Purple. RLC model. Impedance vs. Frequency, without inter-plane capacitance.
- Red. RLC model. Impedance vs. Frequency, with inter-plane capacitance.

The **problem** comes when I change the RLC model to S-Parameter model.

The behaviour shown at Touchstone viewer is not the right response for the capacitor.

Here, is a comparison between RLC and S-Parameter model for the same capacitor.

- Purple. RLC model. Impedance vs. Frequency, without inter-plane capacitance.
- Red. RLC model. Impedance vs. Frequency, with inter-plane capacitance.
**Orange**. S2P model. Impedance vs. Frequency, without inter-plane capacitance.**Yellow**. S2P model. Impedance vs. Frequency, with inter-plane capacitance.

Is the root cause in the S2P model? Or maybe is it needed to include any input to HyperLynx?

* The S-Parameter models are obtained from manufacturer's website (http://ksim.kemet.com/Default.aspx), and before work with them, I have checked the right behaviour of them.

Any help will be welcomed in order to understand the problem, and of course, find a solution.

BR!