I had put a diagram up of the circuit, maybe a bit silly.
Just a simple google search will pull up a raft of hits on designs. They are also linked in to jamming mobile phones.
They are good for about 1000ft on a 45mm antenna. I doubt it would have the same effect on an aircraft because the hull would be shielding the aircraft antenna. But low down or with a hill next to the approach it could get you I suppose. If they could get line of sight to the top of the aircraft.
There used to be one on the Isle of White in the solent that used to sometimes kick in but it never really affected aircraft on approach as we were on vectors by that point. I presumed it was someone yacht racing in the solent trying to stuff up other racers and not anyone out trying to get aircraft.