On Performance Characterization of Harmonic Transponders

Harmonic transponders are passive wireless devices that hold great promise for a variety of long-term tracking and sensing applications. These nonlinear devices receive an interrogation signal at one frequency (f) and backscatter harmonics (typically, 2f is of interest). The device's conversion loss is the change in power from what is received and what is transmitted. We show herein that conversion loss is dependent jointly on interrogation power, interrogation frequency, and interrogation angle. This coupled nature of the device's behavior necessitates performance metrics that capture these characteristics. We present a methodology to generically test these devices and propose metrics that capture the noted dependencies.