dear maryam, i am working about periodic structures. and when i want to simulate a unit cell, i do it by hfss. when i simulate a unit cell by cst, the phase is incorrect. so, i suppose you, simulate your unitcell by hfss again.

and use floq port. and notice about the deemed distance.

maybe your problem is fixed.

regards

If it is S11 then you have almost total reflection anyway - so you are probably doing something else wrong, unless you are looking at the reflection to try to estimate the loss.

If there is not much loss but a poor match the signal can bounce about in the simulation for a long time and then rounding errors become significant and you can get more energy coming out than you put in!  Perhaps you are trying to simulate a high Q resonator to get the loss.  The time domain solver is not a good way of doing this.  The frequency domain solver is the right one for problems like that.

Thanks Malcon White 

I change to Frequency domain solver but for graphene the results are completely different from time domain solver

I don't recognize which results are true

Dear Libimol

I'm using pec-pmc boundary condition in x and y direction

and in the setting i put the reference plane on the stucture

but in time domain solver i'm getting s11 more than 0 dB

I heard that Time domain approach is not good for scattering problem of a Graphene based structures in CST, So probably frequency domain one must be correct.

Take a look at this video.

https://www.youtube.com/watch?v=JPaDT8DgqEI

So much sorry.

Unfortunately, those videos before cooperation of CST and 3DS are not available.

I checked my videos and can't find it. I think I have removed it.