ANTENNA DEVELOPMENT FOR THE AUTOMOTIVE SECTOR
Today, modern passenger vehicles and trucks are equipped with a large number of systems which would not function in the absence of a suitable antenna. These systems cater for communication, data transmission, navigation, remote sensing and, last but not least, radio and TV reception. For some time now, FHR has been supporting industrial companies in the development of such antennas and the associated high frequency circuits.
Traditionally, radar applications are the most important application area at Fraunhofer FHR. For many years already, the scientists have been supporting one the large German automotive suppliers in the development of new generations of automotive radar devices that work in the ISM band at 24 GHz (Fig. 1). These devices are produced in extremely large quantities and, accordingly, the production costs have to be kept to a minimum. This poses a great challenge for the design process. Robustness against production, material and installation tolerances is essential. The fact that millions of these devices have already been installed in over 40 vehicle types speaks for itself.
In the near future, the scientists will, however, also turn their attention to automotive radars with higher frequencies: antenna development for the frequency range around 77 GHz poses new challenges and will also prompt investigation into new materials and production technologies.
Dedicated Short-Range Communication (DSRC) was implemented as the standard for toll collection and access control in Europe. Such antennas allow data exchange between the toll station and the transponder system in the vehicle and are therefore instrumental for electronic toll collection. Fraunhofer FHR is currently developing a DSRC antenna for a company that equips measurement vehicles that are used to control tolling systems. The production costs for this antenna will be significantly lower than those for the antennas that are typically used for this application.
Antennas with a large bandwidth are suitable for ultra-wideband applications. UWB is a technology that is used to transfer large data volumes with short, wideband, low-power pulses over short distances. This technology is also suitable for measuring distances, positions, layer thicknesses or material properties etc. In the automotive area, UWB is used for in-car communication, position determination, measurement of tire pressure and thread depth or for the passenger-related adjustment of the vehicle's man-machine interface. The scientists at Fraunhofer FHR develop the corresponding application-specific UWB antennas for the suppliers of the automotive industry and also give due consideration to the antenna's immediate surroundings. Major challenges here include space requirements, producibility, costs and parasitic interaction with other components.
The external appearance of a vehicle is extremely important when developing a new model and many systems have to be correspondingly subordinated. This also applies, of course, for the antennas. Fraunhofer FHR has extensive experience in the area of conform and structurally integrated antennas and recently developed a complementary Yagi-Uda antenna with directional vertical polarization which radiates along a metallic surface. The antenna is positively integrated into the surface and does not protrude (Fig. 3).
Navigation systems based, for example, on the Global Positioning System (GPS) are now standard in the automotive sector. Fraunhofer FHR has been working on corresponding antennas for many years already. The central focus lies, above all, on miniaturized array antennas which can effectively suppress interfering signals and multipath propagation effects (Fig. 2). In this context, metamaterial technology has led to various innovative solutions.