Unable to increase mesh density/refinements

Hi,

I am a newbie to CST and I am not sure what I am doing wrong here.

I am trying to simulate a printed inverted-F antenna on a FR-4 PCB. The bottom side of the PCB is a solid ground plane except for where the antenna is. The antenna is fed using a coax with a waveguide port. I have also drawn some ground patches on the top side and have them stitched up using vias.

The structure simulates fine under default settings with a relatively large mesh line ratio limit.

For some reason, I don't seem to be able to increase the mesh density. Whenever I tried to increase lines/wavelength or increase refinement along edges or volume for any objects, the simulation either becomes unstable or all the energy are reflected back at the port (shorted). I can't use adaptive mesh generation as well because again the energy gets reflected back on the second pass.

Now I am not sure if I simulated the first pass properly.

you might want to use the local mesh properties to change the meshes.

just to check with you, are you using either open boundary or with added space to your simulation?

Regards
Wang