They used radio on balloons in WWI with Morse code.
Tethered observation blimps used a cabled telephone connection.
It's such a simple and obvious thing to use balloons as data repeaters (which is what Loon does) I can't see why there are patents.
The Elephant in the room is that Loon needs its own licensed spectrum and is irresponsible and pointless. Even if it was sensible, we now know that Alphabet/Google are totally untrustworthy and not fit people to act as an ISP.