Infinite dielectric layer-PML (HFSS)

Hi all,

I'd like to create an infinite dielectric layer on the top of my antenna; therefore I create a virtual object with dielectric and set PML. If I do that; however, the result is incorrect. I think this is because my port impedance has been changed without air box. (If I used the radiation box outside the antenna; the impedance is 45 ohm, but it changes to 2 ohm now.) Do someone know how I should do?

Thanks a lot

Please show me the cross section of your port.
What happens if you define a lumped port?
What is the frequency?