CST Boundary conditions

Hi everyone,

Anyway, I'm just a beginner in CST and your help will be appreciated. I just designed an UWB antenna in CST MWS, the antenna is : microstrip rectangular patch, partially grounded substrate. BACKGROUND MATERIALS set to NORMAL, Waveguide PORT was designed accordingly. Now, here's my problem: BOUNDARY CONDITIONS. When I set them ALL to open (add space), the simulation just looks like in the paper or much similar. When changing them , the result will be different and undesired. Could you share some hints regarding to boundary conditions. Please see the attached image.
Thank you.