C1.1 - A New Concept for Aligning Automotive Long-Range Radar Modules Based on Wireless Microwave Sensing

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
C1 - Wireless Sensors I
R. Weigel, G. Vinci, B. Laemmle, A. Koelpin - Universität Erlangen-Nürnberg (Germany)
366 - 369


A rising number of modern automobiles are equipped with long-, mid- or short-range radar distance sensors. Especially long-range radar based driving assistance systems operating at 77 GHz get more and more into focus to enhance traffic safety. Especially for these long range modules the adjustment of the sensors exactly in parallel to the thrust vector of the vehicle has to be done in an extremely small range of tolerances. If the misalignment angle exceeds +/-0.5° objects outside the lane at maximum detection distance will be misinterpreted as being an obstacle inside the own lane. Up to now the radar beam alignment is only conducted during the vehicle’s assembly in the factory. In the automobile workshops there is no possibility to measure the radiated beam. All alignment tools are based on adjusting the radar sensor housing by optical or other methods and rely on the exact alignment of the radar beam with respect to its module housing. The achieved tolerances of such tools are quite high and cannot be verified.
In this contribution a new method for aligning the radar module by directly measuring the microwave beam is presented. The system is based on the six-port concept that is known since mid of the 1960s for phase measurements with extremely high accuracy. The microwave beam is received by two antennas resulting in a phase difference between their signals depending on the path difference. By superimposing the two antenna signals to each other with four different relative phase shifts this path delay can be evaluated. The path delay is a direct measure of the angle-ofarrival of the radar beam at the antenna plane. As the delay evaluation is done before downconverting the signal to baseband, the accuracy of the system is extremely high. By placing the six-port setup in front of a car its radar beam alignment can be evaluated with a resolution of 0.05° even without any filtering and post processing of the measured data. The angle resolution can be further increased by this post processing.
A demonstrator circuit of the complete analog (microwave and baseband) sensor module will be shown and measurement results for a 24 GHz automotive radar system will pe presented. As the six-port concept is a universal wireless sensor for angle-of-arrival measurements, its application is not limited to automotive radar module alignment. It can be a useful tool for any phase difference measurement problem.