Radio aerial query

My 2004 Transit just had a new windscreen fitted, in the process the side mounted radio aerial was broken away from the wing.
I'm trying to work out how the connections work.
The original mounting inside the wing was badly rusted, leaving just a rusty spade connection dangling. The actual aerial connection was a cable with a banjo-type metal end-piece which attached to the aerial section.
The radio seems to work with or without the aerial connected. Reception has always been patchy on the move btw. Obviously, I can re-connect the aerial easily enough, but I've no idea where the dangling spade connector originally went. The rust has eaten away at the surrounding area, so there's no clue there.
I'd really appreciate an explanation as to how the aerial should be connected, and why the radio seems to work without it!