For Improved Road Safety

Ko-TAG Directional Antenna

Detecting unexpected traffic hazards demands an efficient, compact, robust, error-free antenna system. Fraunhofer IIS scientists have developed a directional antenna system that meets these criteria. 

Driver assistance systems on the rise

Driver assistance stystems are used more and more often in recent years. They heighten drivers‘ awareness of their surroundings and help them respond accordingly: Vehicles automatically monitor the situation around them based on data they wirelessly exchange with other road users. In the future, automobiles will be able to communicate both with one another and with their surroundings, which is known as car-to-car and car-to-X communication, respectively. This improves safety on our roads. A key element of the sensing technologies involved is the Ko-TAG directional antenna.

Accurate direction finding

The Ko-TAG directional antenna identifies road users such as pedestrians or cyclists in its vicinity, provided that they are carrying an active transmitter embedded in a piece of clothing, satchel or mobile phone. An antenna system on board the vehicle determines how far away each identified object is and in which direction. Distances are derived by measuring the time it takes for a radio signal to travel from the tracking unit to the transponder and back. The combination of distance and angle measurement enables precision tracking.

In addition, inertial sensing is used to determine a person’s walking speed and direction. Tracking a pedestrian’s path makes it possible to predict where they are going to step into the road even if they cannot yet be seen. The expected area can then be closely scanned for shapes or even partial shapes, e.g. legs or head, of pedestrians.


Greater road safety


Once the system has detected a pedestrian, the risk of colliding with the pedestrian can be calculated. However, since both the pedestrian and the driver may act and react in a variety of ways, a collision is impossible to predict with absolute certainty until it is imminent. For this reason, a statistically based behavior model is additionally used.

If there is a risk of collision, the system will either warn the driver or take action to avoid it: If the time to collision exceeds 1.5 seconds, a warning signal is sounded. Otherwise, the system can bring the car to an emergency stop.


Technical data

Detailed view of Ko-TAG directional antenna’s backside
© Fraunhofer IIS/Thomas Endres
  • Number of elements: Six
  • Frequency range: 5.725–5.925 GHz
  • Matching: VSWR < 1,5:1
  • Gain: 5 dBi(c)
  • 3 dB beamwidth:
    • Linear polarization: 100°
    • Circular polarization: 70°
  • Isolation between elements:
    • Linear polarization: >18 dB
    • Circular polarization: >28 dB
  • Polarization:
    •  Linear with broadband matching
    •  Circular with four-point feed
  • Axially symmetric design:
    • Identical directivity and phase centers across all elements
  • Cost-efficient design:
    • Very low-loss miniaturization
    • Three layers
    • Small dimensions: Ø 120 mm, max. height 8 mm

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Ko-TAG directional antenna

Research initiative from Federal Ministry for Economic Affairs and Energy

Ko-TAG is a collaborative research project aimed at improving road safety. Fraunhofer IIS’s involvement centers on the angle measurement and inertial sensing components required for a dedicated tracking system. Additionally, Fraunhofer IIS is conducting research into the classification of vulnerable road users’ movements in order to enable reliable and timely hazard detection.