Comment by ssl-3

My (old) E36 BMW had a switched multi-element array in the rear glass that served as the FM antenna.

It had a magic box that used feedback from the stock radio's IF section to (try to) erect the best pattern for good reception at any given time, and which presented one unified RF output to that radio's singular input.

Cadillac has used the same, or very similar, system as well.

Which is neat and all, I guess, but we seem to be getting off into the weeds: These antenna elements were not invisible at all except for the fact that they blended in with the heated defroster elements that were also printed onto the glass.