Hidden Antennas on Vehicles
There are a large number of antennas hidden from view on many of today´s automobiles. Different antennas cover radio and television reception, telephone and navigation systems and increasingly digital radio reception. Hidden antennas invariably suffer from performance problems due to shielding from the vehicle and simple diversity systems have become common for broadcast reception.
The window glass areas on cars are popular places for printing radio and television antennas and more recently a cut out in the roof incorporating a glass sunroof panel or plastic panel has been used. In our research we have investigated and compared the performance of antennas placed in these regions. The inclusion of seats and other interior trim panels is being investigated as these have significant effects at higher frequencies.
The studies have involved computer predictions using both CST Microwave Studio and FEKO software, validated where possible by measurements. The FEKO package combines the Method of Moments with the Uniform Theory of Diffraction while CST Microwave Studio is based on the Finite Integration Method. Each package was able to import 3D data of the car body and mesh it electromagnetically to compute the antenna performance. In addition each package can handle dielectrics within the structure. The currents excited by an antenna hidden in the roof aperture of a car are shown below and we can determine the overall performance of the antenna system such as the impedance and radiation patterns. Much of this work has been carried out in collaboration with Harada Industries.