DRAW VIA HOLE

Hi Alan,
in order to draw a via hole in HFSS you just need to draw a cylinder having the desired radius between two conductors on different layers (for example, between the ground plane and the signal layer of a microstrip).
Via holes have a metallization on the inner surface of the cylinder. So, the volume inside must be subtracted from the dielectric substrated crossed by the via itself.

So, summarizing:
1) Draw the cylinder;
2) Subtract the cylinder from the dielectric substrate;
3) Select the cylindrical face in the subtracted region;
4) Apply PEC boundary or Finite Conductivity boundary (so as you can define material ,thickness, roughness, etc.);

Since via holes introduce a parasitic reactance and generally they are not perfect short circuits, thickness of metallization and cylinder radius become fundamental parameters in via holes' design. I advise to run a parametric analysis varying radius and thickness in order to reduce parasitic reactance.

Hope this helps.

tq very much ivan.
regard alan