Precise distance measurement with cooperative FMCW radar units

In many applications the precise distance between different units has to be measured. The proposed measurement system operates with frequency modulated continuous wave (FMCW) radar sensors for distance measurement in a cooperative but unsynchronized way. Due to the missing synchronization a data transfer between the units is performed by means of the radar hardware. On the other hand, this principle could be easily implemented in communication systems. A prototype system in the 5.8-GHz ISM band has been built, and measurement results up to about 780 meters distance with accuracies of few centimeters are shown. Furthermore, the distance can be calculated at both transponder units.