Distributed Repeaters for Extending the Range of Passive Harmonic RF Tags

Passive harmonic radio frequency (RF) tags are favorable for their ability to perform in cluttered environments where access to the tag for battery maintenance is difficult and time consuming. A crucial limitation with passive harmonic RF tags is their range and the large amounts of power that is needed to turn on the nonlinear device that will retransmit the harmonic of the incident signal. In this paper, harmonic RF tag repeaters are introduced to increase the range of the tag while also increasing the power incident on the tag that turns on the nonlinear device that produces the harmonic signal. A 2.4GHz and 4.8-GHz bi-directional repeater is used to amplify the fundamental and harmonic signals between the source and the RF tag. Measured and simulated results indicate that with the inclusion of repeaters, the range of the passive tag is improved more than 3 times from 2-m to at least 6-m with only 1 repeater and the power incident to turn on the nonlinear device is improved with distance.