Surface in volume mesh

I have 2 stp files: a volume and an antenna, I load and mesh them as follows:

logging.info('importing volume step file')
volumeGeo = OCCGeometry('../../../../data/TOMAS_data/volume.step') # "OCC internally uses mm per default and we do not change that. 

logging.info('importing 3D antenna file')
AntennaGeo = OCCGeometry('../../../../data/TOMAS_data/Antenne.step') # "OCC internally uses mm per default and we do not change that. 

#https://docu.ngsolve.org/latest/i-tutorials/unit-4.4-occ/occ.html
geo = CSGeometry()
volumeGeoShape = volumeGeo.shape - AntennaGeo.shape

geo = Glue( [volumeGeoShape.mat("fluid"),AntennaGeo.shape.mat("Copper")])

with TaskManager():
    ngmesh = OCCGeometry(geo).GenerateMesh()

However this also creates a volume mesh for the antenna, how can I mesh the volume normally but make the antenna only a surface mesh? Or is this only possible by meshing first and merging afterwards?