Thanks for your reply
I am not sure I understand why my ports have improper range, the settings are in um and ports are um size. I will change to nm and see what happens.
I never had that background material error, I assumed the software takes the surroundings to be air by default. What cst version are you using?
Lastly, can I ask what simulation you ran: Time domain/ Freq dom/(...), what frequency range, etc. I am interested if you have made any other changes to the settings in the file I uploaded so I know what to improve, like meshing for instance, not sure if meshing is done properly.
Thank you