On the Use of Additional Transmitters for Increasing Detection Range in Harmonic Radar

Harmonic radar is commonly used in localisation and tracking applications where weight and size restrictions do not allow the use of active radio transmitters. It relies on the operation of a passive transponder tag attached to the target that creates a harmonic response when illuminated with a radio signal. The main bottleneck of harmonic radar systems is low conversion efficiency of the tags and, as a consequence, low detection ranges. In this paper, we propose an approach to increase maximum detectable range by using additional helper transmitters that emit an unmodulated carrier. We analyse the harmonic tag response to a superposition of transmitted signals and show that it yields an amplitude gain in the tag output signal. As a result, we can increase the detection range by a factor proportional to the number of additional nodes while keeping the system cost-efficient and lightweight.