[Request] Fuel usage for wifi antenna

Saw this in an article https://www.ft.com/content/5fec5349-defb-4c3a-9362-bed4661ba7ea

"[O'Leary - CEO of Ryanair] said the airline would install WiFi “in a heartbeat” if the antenna could fit inside a plane rather than on the outside where they raise fuel costs by contributing to drag."

How much additional fuel will a wifi antenna use per 100km?