A Software Defined Radio Interrogator for Passive Harmonic Transponders

Passive wireless sensors provide an opportunity for long term monitoring of remote environments. Such devices are activated with an interrogation signal which enables them to transmit information via a return signal. Some systems utilize the same frequency for interrogation and the return, which causes unwanted interference, particularly in cluttered environments. This work considers an interrogation system for a different class of passive devices, i.e., passive harmonic transponders. Specifically, we present the results of a single-board software defined radio (SDR) interrogation system which transmits an interrogation signal at 1.3 GHz and receives a return at 2.6 GHz. The system is demonstrated with a device known as a passive, chipless frequency doubling reflectenna (FDR). The SDR platform enables a compact, low-cost, and quickly operating design. The mean absolute error of the proposed interrogator was found to be 1.15 dB when compared with laboratory instrumentation. Additionally, this system is capable of interrogating at 70 cm with an EIRP of only 0dBm.