A DAB Antenna will require a separate fixing. I got a car sunroof specialist in Bristol to fit mine, as the interior roof lining fabric looked a sod to get off after removing a few bits and bobs.
The separate fixing is required because the aerial has a separate DAB signal wire and an FM (frequency Modulation) wire. It also has a 5 Volt (i think its 5!) DAB booster wire and FM booster wire but it is not essential that these are wired in if u live in a strong signal area.
What you find on most DAB radios is that if the DAB signal is weak, the radio will switch to a comparible FM station (if u want it to). Personally I didnt bother having the FM reconnected.
You will need to route a DAB cable from the new aerial connector on the roof to your radio/DAB control box.
Hirschmann do the DAB aerial that ive got called AUTA 16 V DAB and ive had no problems whatsoever.