Hi moj14mja,
While exporting the 2d geometry in HFSS to DXF, only the geometry located at XY (i.e, Z=0) plane is exported. I think in your design ground and probe are at principal XY plane, so it is getting exported. your patch is at some height above the XY plane. To solve this you may follow any one of folling steps.
a) Move the patch to XY plane (making height of substrate to zero would be easy to do that) and then export the geometry to DXF.
or
b) Create relative Coordinate System to shift the location of Origin to patch. Export to DXF.
Hope this helps...