Crystal simulation wit S parameters not correct

[stevegeers]

I am trying to simulate a crystal filter using measured S parameters. There are a couple points in the response that indicate that the passive circuit has gain. The points are interpolations between the points in the  S parameter file. All points not in the sharp peaks agree with measured data on actual hardware. I have seen this in other programs in the past when modeling high Q circuits. It is usually a numerical accruacy issue due to rounding. Is there any way to adjust the numerical accuracy or anything else in the simulation to resolve this?

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   crystal_gain_plot.png
   

[Carsten]

similar things happen in CST, when S-Params from an 3DEM-Simulation need to be interpolated. In that case it helps to change s-param interpolation from polar to cartesian domain.

Qucs offers similar options in touchstone file component. maybe that helps?

 

[stevegeers]

Changing to cartesian interpolation fixed the issue. Thanks.

[Carsten]

@Michael: Vlt. ließen sich solche Fälle automatisch erkennen und Qucs könnte eine Warnung ausgeben?

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