Transparent film antenna for a vehicle window

Claim 1

An antenna for receiving and transmitting electromagnetic radio waves from a motor vehicle, the vehicle having a metallic structure forming an aperture with a window glass disposed therein, the window glass having an upper region and substantially horizontal top and bottom edges interfacing with the metallic structure, the antenna comprising: a principal element formed of a thin transparent film of electrically conducting material supported by the vehicle window glass, the principal element being horizontally elongate and having a generally rectangular shape with upper and lower edges separated by a width W, the upper edge of the principal element being spaced at a distance D from the top edge of the window such that the sum of W and D does not exceed one-third of the distance separating the top and bottom edges of the window, thereby confining the principal element to the upper region of the window glass; means for electrically feeding the principal element with respect to a ground point on the vehicle to effectively couple the principal element electromagnetically to the vehicle metallic structure; and means for tuning an antenna impedance developed between the principal element and the ground point on the vehicle, the tuning means comprising an auxiliary element formed of the thin transparent film and shaped as a vertically elongated rectangle, the auxiliary element having an upper end electrically connected to the center of the lower edge of the principal element and extending downwardly therefrom to provide a T-shaped antenna configuration, the auxiliary element having a specified length, which influences the impedance of the antenna.