Motor vehicles are increasingly equipped with driver assistance systems, which with the aid of sensor systems detect the environment and from the thus recognized traffic situation derive automatic reactions of the vehicle and/or instruct, especially warn the drivers. Here, a distinction is made between comfort and safety functions.
As a comfort function FSRA (Full Speed Range Adaptive Cruise Control) plays the most important roll in the current development. The vehicle adjusts the true speed to the desired speed predefined by the driver, provided the traffic conditions permit this, otherwise the true speed is automatically adapted to the traffic situation. As a second important safety function the lane change assistant currently establishes, which indicates to the driver and/or warns him with a set turn signal, if there is another vehicle on the adjacent lane, which has to be observed when changing the lane, in particular to avoid accidents and hazardous situations, which would force this other vehicle to brake sharply or to make an uncontrolled lane change on his part.
In addition to an increase of the comfort, safety functions are increasingly the focus, whereby the reduction of the braking and/or stopping distance in emergency situations plays the most important role. The spectrum of the corresponding driver assistance functions extends from an automatic priming of the brake for reducing the brake latency (pre-fill), via an improved brake assistant (BAS+) up to the autonomous emergency braking.
For driver assistance systems of the above described type radar sensor are mainly used today. Also at poor weather conditions they work reliably and can measure in addition to the distance of objects also directly their radial relative speed via the Doppler effect. As transmission frequencies, here 24 and 77 GHz are used.
Currently available radar sensor only have a frontal detection area of at maximum approx. −75 . . . +75°. For implementing a high-performance lane change assistant, however, it is necessary that the detection area further opens towards the side, so that one can look quasi around the corner; this is in particular important for situations, in which the own vehicle passes slowly another in particular smaller vehicle and the latter is in the dead angle region of the side mirrors. In order to realize such a laterally extended detection area, according to the state of the art either a second sensor with another installation orientation or at least an additional, differently oriented high-frequency printed circuit board is necessary, which increases significantly the system costs.