You have first to add some air above the microstrip line with the "backround
material" tool and then set the boundary conditions to electric. It would be
better not to put symmetry planes because you have a quasi-TEM wave, else you may take incorrect results..Good luck!
hi,
yes you do need to put air because otherwise your PEC boundary above the microstrip line would be in touch with it, shortcircuiting it. I am not sure but probably CST would give an error message, or at least a warning message.
regards
Dch316 is right,CST will not probably give an error message, but if you do not
put air above te microstrip line your structure will automatically become a planar waveguide..You must do the same thing if your ground plane is interrupted (i.e holes etched in ground,EBG stucture).In that case you must also be carefull while setting the waneguide ports