What about a hidden power antenna? I've seen them on Street Rods but have no idea how well they work. When down, you would only see the small tip of the antenna. File it to match the contour of the fender and paint it body color and it will pretty much disappear to the casual observer. All mounting hardware is under the fender.

I couldn't find a picture of it on a Street Rod, but, did find a kit: antenna .