HFSS ACIS/SAT file to convert into STL

Hi All,

I have a 3D ACIS/SAT file which is exported from HFSS.
What I want to do is to convert the file into Stereo Lithography format (STL).

I tried a CAD software, Alibre Design Professional. The software can import the file and also can export STL file.
The original data is of a slot array antenna so there should be many slots but STL data doesn't have any slots.
The original ACIS/SAT file looks NO SOLID data in the Alibre's Software, just like a line/surface without thickness. I guess the ACIS/SAT file lacks the information of the thickness of the component, I don't know exactly.

Anybody out there have solution on this?
The data cannot upload here, I'm sorry (I don't have HFSS, but only the data).

Thank you in advance.