lossless or lossfree boundary in HFSS

How do I simulate lossless or lossfree boundary in HFSS?

I usually take my airbox as the boundary with a lossy PEC material, but now I would like to have a lossless boundary.

Thanks.

could someone please reply to this post?

Basically, I would like to prevent the antenna from radiating outside a small chamber. Do I use lossy or lossless boundary? I say lossless, but I need confirmation.

Thanks.

To Terminate Radiation you can use PML or Radiation Boundary.

Thanks. I did that in simulation. How about is in a real setting? What do you use? Anechoic chamber? If so, are there small anechoic chambers out there, say 20cmx20cmx20cm?