Detecting Vulnerable Road Users Utilizing the Harmonic RCS of Active Tags at 79/158 GHz

Vulnerable road users have not been able to benefit equally from the improved traffic safety supported by automotive sensors. In 2020 this culminated in traffic fatality highs of more than 30-years for pedestrians, motor, and pedal cyclists. Regarding radar sensors, vulnerable road users suffer from a lower RCS compared to other vehicles like cars and busses. Accordingly, their detection is more challenging, especially while being surrounded by those vehicles, as is common in city traffic. Therefore we have presented a harmonic radar system which allows for tag based detection inside of a seperate receive channel. In this work we present fundamental and harmonic RCS measurements of a bicycle equipped with the tag, to allow for the comparison to other approaches. While its fundamental RCS is exceeded by large metal objects, the harmonic RCS increases with range, as long as the tag is saturated. Thanks to the clutter-free receive channel, even a relatively small level, which is determined by the tag's saturated output power, is sufficient for detection.