non-symmetric S-parameter in HFSS

时间：03-23 整理：3721RD 点击：

Did anybody ever simulate symmetric structure (e.g. CPW, microstrip) in HFSS 9.2 ? It is really ridiculous, the S11 is not the same as S22. Any comment on this?

The reply may not be relevant to the above question directly but I felt I needed to thell that in CST-MWS 5 , I simulated a microstrip and it is clear that S11=S22 and S12=S21 ( symmetrical structure ).

-Arun

S11 and S22 will not be equal unless the mesh is also symmetric. Since HFSS uses adaptive meshing, the mesh will almost certainly not be symmetric. FDTD codes uses a cartesian gridding; by its very nature this gridding is symmetric.

However, S11 and S22 should be very close. If they are not close, I suspect you have an error in your setup.

If your model is a device , like power divider, the S11 will not equate to S22.

I agree with you, I also thought about it. My result shows less than 1 dB difference. However, I was wondering where the HFSS start to generate the mesh. Is there any trick to make the mesh symmetric?

Hi,

HFSS allows you to control the accuracy of your solution.
Please do the following:
1) Increase port solution accuracy from 2% to 0.1%
2) Increase solution accuracy from 2% to 1%

In order to speed up the simulation on "simple" problems (CWG,MS,Diff Pairs), do the following:
3) Increase adaptation per pass from 20% to 30%
4) Set seeding on the traces with a minimum mesh of width of the trace.
5) Use Wave Ports in Driven Terminal instead of Lumped ports and use De-embeding. For example instead of simulating a trace that is Lambda long, simulate only 1/4 Lambda and deembed another 3/4 Lambda.

Regards,
Itai Frenkel