Annular slot windshield antenna

An automotive AM/FM hidden antenna using the slot between the body of the automobile and a metal solar heat-reduction film in the front windshield is described. Such solar heat-reduction metal films are becoming common and thus represent an opportunity to incorporate an antenna at only marginal cost. The radio frequency (RF) input impedance and gain patterns are described, and techniques for impedance matching are shown. Theoretical and experimental antenna patterns are compared. A test range measurement system and experimental results is described. A mobile on-road system to characterize the antenna in urban and suburban environments is shown. The application of this mobile system to the measurement of calibrated gain patterns is also demonstrated.