Characterizing Harmonic Transponder Performance Jointly Over Frequency and Power

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
0
) and return its harmonics (typically, 2×f
0
is of interest). Due to these separate bands, over-the-air (OTA) laboratory characterization of these devices typically leverages a signal generator on the transmit side and a spectrum analyzer on the receive side. Herein, we present an approach that instead uses a standard two-port vector network analyzer (VNA) for both functions and demonstrate its use. The advantage of this approach is that high resolution measurements can be quickly made jointly over frequency and over power. This approach can thus characterize devices whose resonant frequency may change with a locally sensed phenomena or by the environment in which the device is deployed. Our OTA measurements are within ± 0.5 dB of those using a high-end VNA having advanced capabilities. Our results also provide greater insights on the coupled nature of interrogation frequency and incident power on the device’s response.