HFSS Instantaiation and radiation pattern

I have two antenna designs in hfss. I want to include one antenna into other antenna file (instantiate design in cadence). Is there any way to perform this function in hfss?

When we set the boundary in hfss, it computes maxwells equation on this boundary?. If so, the radiation pattern will be reliable only at that boundary or at infinite distance?

I did not understand your first question.

Yes, HFSS computes fields on the outer Radiation boundary and then it calculates the Far-field Radiation pattern from the calculated field quantities (on Radiation boundary)