HFSS air box problem

Hello everyone,

I have a question, so I need your helps, please.
I don't know that why we can use the two different dimension vacuum box in HFSS for the dipole antenna simulation at 900MHz? And we just add the radiation boundary for one or both box?
Thank you very much!

Why does this thread say it's solved?

And why would you want two vacuum boxes?

Hi, Thanks for your attention. Actually, I have just used HFSS. I want to simulate a microstrip dipole antenna. It's a simulation which I have seen from a document. But I don't see more explains.