I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on the magnet. Consider also that most cars have a coat of paint between the mag mount and the sheet metal. Both of these should result in some level of electrical isolation between the antenna feed shield and the sheet metal.
I guess what I'm simply not clear on is how a mag mount antenna's ground plane is connected electrically. Or is this accomplished through inductance?