Electromagnetic characterization of automotive sunroofs for car-to-X applications

For Car-to-X communication at 5.9 GHz effects of electromagnetic wave propagation inside and along the sunroof of cars are investigated by means of modal analysis of a dielectric slab waveguide, numerical modeling by finite integration technique and measurements. Since the field is guided inside the glass as fundamental TMo mode and overlaid by free space radiation, interference effects reduce the range in forward direction, an important disturbing effect for car-to-car communication. The influences of roof curvature as well as window size and position on wave propagation and radiation are investigated. Deep nulls in the radiation pattern are found in direction of the forward corners of the glass roof. Metallized sunroofs are shown to improve forward radiation and nulls by at least 6 dB. Computational results are evaluated by measurements on a whole car in an open site test range.