I always have problems setting boundary conditions (Open, add space, Et=0, Ht =0, etc.) in CST Studio Antenna Simulation Software.
Please find the attached figure. I designed all the antennas here and none of them exactly match with S11, they are way off, example the measured freq. is at 2.20 GHz where simulated designed freq. was at 2.45 GHz. Only the rectangular patch antenna match (~2.48GHz), while others in the Figure don't, and they are way way off !! Recuangular patches have full-ground plane but others have different ground sizes as shown in the Figure. Other parameters of the simulation and fabrication are okay, but I noticed the boundary conditions and radiation box size make a huge difference. For the measurement, I used VNA and absorbers all around.
Please let me know what is the porblem here. I found in places they suggest keeping all side 'open and add space' except waveport side where it should be only open. Still it didn't work. Tried all other settings. I use SMA 3D model as waveport, as shown.
Please suggest me the appropriate boundary settings for 1,2,3,A,B. And with possible theories as to why.
First, you should use open/radiation boundaries or PML boundaries for these kind of simulations. A PEC (Et=0) or PMC (Ht=0) would be incorrect as Smrity Dwivedi explained. If your open boundary is more than lambda/4 away from all sides at the lowest operating frequency you should get consistent results.
Second, have you considered the possibility that the discrepancy between your measurements and simulations could be due to material properties and not the boundaries?
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