what kind of boundary should i set ?

i use hfssv9 to simulate the structure like the attachment describes, i use an air box and add radiation boundary and want to get the s12 curve , but the simulate result doesn't match the results in my reference paper, anybody help me???

I did make some changes but still having a very poor response.
Try in you side to see if you can get the results you expected.
Would you post the paper or send it to me so I can have the
reference?.

jallen , if you try to set the substrate four sides as PerfectH, and clear the airbox, then is the result. i have solved the problem, but always thanks a lot!