Hi Kevin:
the main reason you didn't find one is the glass losses!
at 2.4GHz, the loss of most kinds of glass winshields are made of, is
so hi as to defeat operation!
using a different base, such a cellular one will work, since it has a
high pass filtering characteristic, but like I said, the glass itself
can prove to be an insurmountable hurdle.
Saandy 4Z5KS