Simulating 2D periodic structure in CST and the s-parameter

Dear all,
I am trying to simulate a 2D metal mesh filter structure, however I am not quite sure the obtained s-parameter magnitude in linear expression is corresponding to the power or amplitude? As far as I know it doesn't really matter in db expression.
Many thanks in advance.
Regards,
hfj1010

The db expression is derived from the linear results, therefore, if your linear results are not reasonable, why your db-results should? Maybe post your results.