In order to enhance a vehicle's aesthetic qualities, it is common to integrate the vehicle radio antennas with one or more of the vehicle's windows (commonly known as hidden antenna systems or on-glass AM/FM antenna system). Unlike mast (rod) antennas, on-glass antenna systems do not introduce any external vehicle protrusions and they typically offer excellent mechanical stability and satisfactory reception performance. Although on-glass antennas are widely used, they do suffer from various drawbacks. Specifically, on-glass antennas are difficult to design because a small change in a vehicle's body design can radically change the reception performance of the antenna.
On-glass antenna systems are usually fabricated by printing metallic conductors on an inner surface of the back-glass or the side-glass of a vehicle window. A low-noise-amplifier (LNA) circuit is typically mounted in close proximity to the on-glass antenna and is electrically coupled to the on-glass antenna to amplify the weak signal received by the antenna before it is sent to the radio receiver for further conditioning. The on-glass antennas are typically fed vertically (close to the vehicle roof) so that the LNA circuit can be housed in the vicinity where the vehicle roof intersects the window. Recently, vehicle designers have found it advantageous to place side-airbags in the locations where the LNA circuits have traditionally resided. Accordingly, new feed points for the on-glass antennas and for the placement of the LNA are required. The most obvious approach is to simply rotate the current on-glass antenna design by 90 degrees which would enable a horizontal feed from the LNA circuit to the on-glass antenna. However, this approach has been shown to tremendously degrade the reception performance of the on-glass antenna rendering its reception quality so poor that it no longer meets the performance specified by many vehicle manufacturers.
This invention sets forth various on-glass window grid antenna designs that can be fed horizontally while still maintaining excellent reception performance characteristics.