Ascertaining Operating Points of Harmonic Transponders Using Intermodulation Responses

Harmonic transponders are nonlinear, passive devices that typically receive an interrogation signal at one single frequency and reradiate harmonics. In this work, we propose leveraging the device’s nonlinearity by interrogating with two closely spaced signals and then measuring the second harmonics and nearby second and fourth intermodulation distortion products. Our results show that we are able to remotely determine the power incident at the device, over a 25 dB range and within ±1 dB, using only the relative ratios between these received components. This result has applications in characterizing the loss of unknown channels and in conducting over-the-air characterization of fully integrated transponders. We demonstrate this latter application.