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Antennas for automotive radar

Blick auf die einzelnen Baugruppen eines 24 GHz Automotive Radar Front-Ends der Fa. Hella KGaA Hueck & Co.
© Photo Hella KGaA Hueck & Co

Blick auf die einzelnen Baugruppen eines 24 GHz Automotive Radar Front-Ends der Fa. Hella KGaA Hueck & Co.

Ein rückwärtiger Automotive Radarsensor der Fa. Hella KGaA Hueck & Co. in in einer reflexionsarmen Messkammer.
© Photo Hella KGaA Hueck & Co

Ein rückwärtiger Automotive Radarsensor der Fa. Hella KGaA Hueck & Co. in in einer reflexionsarmen Messkammer.

Manufacturers enhance the safety of our cars and assist the driver in critical situations through the integration of modern sensor technology. To ensure that the components of onboard radar systems operate reliably in all conditions, the scientists at FHR provide valuable support to the automotive industry in the development of antennas and the positioning of the devices on the vehicle.

Road accidents with injuries and fatalities are often the consequence of inappropriate speed or insufficient safety distance. Distance warning systems that use radar sensors can help remedy this problem. They continuously measure the distance to the vehicle in front and issue an acoustic, optical or haptic warning if the distance preset by the driver is undercut. Distance warning systems significantly reduce the probability of an accident in dense traffic.

Scientists at Fraunhofer FHR are currently working on the development of new antennas and high frequency circuits for the next generation of the on-board radar from the German automotive supplier Hella KGaA Hueck & Co. This system is based on an innovative 24 gigahertz radar sensor and offers safety features that were previously reserved for the luxury class at an affordable price – also for compact and middle-class vehicles. Equipped with just two sensors, the rear radar offers four different functions:

  • Areas behind the vehicle that cannot be seen or are difficult to see are monitored and objects in the »blind spot« are detected (blind spot detection, BSD).
  • The so-called lane change assistant (LCA) warns the driver of dangerous situations when changing lanes or overtaking. The range of approx. 70 meters gives the driver adequate time to react, particularly in highway traffic.
  • Vehicles approaching from behind are monitored permanently. In the event of an impending collision measures are taken to protect the occupants, e.g. tightening of the seatbelt or adjustment of brake hydraulics (rear pre-crash, RPC).
  • When reversing out of a parking space, indiscernible cross traffic is detected in good time and a warning is issued (Rear Cross Traffic Alert, RCTA).

Capabilities such as the precise determination of the distance, angle and relative speed of the objects, correct lane classification and the detection and differentiation of roadside structures open up potential for further applications, such as the speed and distance-regulation system ACC or further pre-crash functions. Various European and Asian vehicle manufacturers now use the lane change assistant in series production. It has already been integrated into more than 25 different series, and others will follow.

Due to their many years of experience in the construction of conform antenna arrays and the integration of antennas in vehicles, the employees of Fraunhofer FHR play a decisive role in the design of the front-end of the 24-gigahertz radar. The antenna and the corresponding high frequency circuits take the form of a multilayer printed circuit board. Tasks to be carried out at Fraunhofer FHR include the design of the circuit board with full-wave simulation tools, the optimization of the radiation pattern, the characterization of the used materials for the predefined operating frequency, the optimization of the housing and radome as well as the measurement of prototypes.

Of particular importance is the selection of a suitable installation point on the vehicle where the characteristics of the antenna are not impaired due to interaction with the carrosserie (e.g. bumper and mounting) and full functionality of the sensor is guaranteed. The techniques for the numerical modeling of electromagnetic fields developed at the institute could make an important contribution. In the near future, the construction data of the vehicle and the antenna will be used in simulations prior to the series production of a new type and favorable installation points will be analyzed. Due to the large dimensions of the vehicles – compared to the wavelength – this poses a big challenge, even for high-performance full-wave simulation tools.

In addition to warning the driver, the driver assistance systems of the future will – provided the necessary legal requirement are met – intervene actively in the driving process, e.g. carry out swerving or braking maneuvers. This will prevent collisions and protect other road users, e.g. pedestrians or cyclists and can be seen as a further step towards improved road safety.