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How to use PML in CST Eigenmode Solver?

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Full Member level 1
Dec 11, 2003
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Hi All,

I am new to CST. I have been a HFSS user for over 3 years. I have been using HFSS for eigenmode solutions to Sievenpiper structure and other periodic structures. In HFSS, PML can be used in the eigenmode solver to simulate free-space...that is my structures are open to air. However, in CST it appears that I cannot use PML (open boundary conditions) for the eigenmode solver. How can I simulate periodic structures that are open to air such as the Sievenpiper structure. Your help is appreciated in this matter. I noticed that the CST examples all have PEC boundary conditions.

eigenmode cst

savedadogs said:
Hi All,

I am new to CST. I have been a HFSS user for over 3 years.

My personal advice would be to stick to HFSS. CST MWS is not the new kid on the block. It's more like the "new shit on the block" and it's unstable.

HFSS is far more stable and give more accurate results that MWS.

CST MWS is heavily dependent on the computational cell that you're working while HFSS gives you more freedom.

I would have to disagree with em_solver,

I have simulated some periodic structures succesfully with CST,
but never with eigenmode solver.
What exactly are you trying to find with eigenmode solver?


cst eigenmode

I wonder whether you attempted to calculate the bandstructures of periodic structures. Like the bandstructures we have seen for photonic crystals. Also, did you try periodic boundary conditions for the eigenmode solver?

cst eigenmode solver

I want to use the eigenmode solver to create the dispersion diagram of the periodic structure. As I merntioned, CST will not let me use an open boundary condition for the eigenmode solver simulation. How can I setup the structure so that there is an air region (free space) on top? It does not seem possible...only thing I can think of is to make a large airbox and use tangential-E bounary condition. Anyone have suggestions?

cst examples

maybe I can help u, wenn u post ur simulation files

eigenmode solver

You can build a large enough airbox and use PEC or PMC bounary condition to the airbox according to the periodic boundary conditions.

eigen mode solver

burton said:
You can build a large enough airbox and use PEC or PMC bounary condition to the airbox according to the periodic boundary conditions.

Hi, I am also using the CST eigenmode solver. May I know how big should the airbox be as I was suggested by CST info to use this similar technique of an airbox? I am trying to obtain the multiple modes of a dielectric resonator in freespace when used as a dielectric resonator antenna. thanks!

eigenmode solution solver

Hi, em_solver

As I know, CST MWS is more accurate convenient and than HFSS in eigenmode solver.For example, it is not necessary to guess the highest frequency if CST MWS, while it is necessary to accurately guess in HFSS.

dielectric resonator antenna eigenmode


From my experience HFSS has more reliable and accurate eigenmode solver than CST (especially to calculate something lossy).
The fact that you need to specify lowest frequency in HFSS is a plus, because sometimes I need to find high order mode solution and it's not
possible to do it precisely with CST (you have to specify - 20-50 modes for example). Moreover with CST you are limited with boundary conditions
(E&H are only apply to main symmetry plains, no impedance boundary, no pml).
And the main drawback of CST is that there is no subgreeding mesh available for the eigenmode solver still.
For a certain geometries CST requires too large mesh and few days for the calculation.

transient, eigenmode solver comparison


don't want to be malicious, really interested if anyone ever got CST adaptive meshing to converge? It never happened to me even in the cases of very simple structures.


cst solver

Hi flyhigh !

I did some experiments with convergency both with CST and HFSS.
With HFSS all is OK and clear for me (if you defined a nice outer boundary approximation the result is converged very well)
But with CST I found the freqs are converged well only to a certain value (~1 %) and if you would like to be more presize,
the convergency to 10^-3 or 10^4 goes very slowly. To get the same value as HFSS predicts CST needs 10-th times more time !
I did this test with sphere geometry.

eigenmodes cst

i used an airbox above the top patch of the periodic structure
however i couldnt get the correct results for mushroom type EBG

for mode 1 i get frequencies equal to 0 for the whole part of Brilliun zone.

also i dont know what should be start and stop frequency for any periodic structure.
i get differerent results when i change the frequency range

anyone who has successfully simulated the dispersion diagram using CST MWS please share your findings


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