Efficient and ultra low mass harmonic radar transponders for insect tracking applications

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University of New Brunswick


The design, construction, and performance of a harmonic radar transponder with a total mass of approximately 530 µg is presented. The transponder is intended for insect tracking applications and consists of very fine wire and a small Schottky diode. It is designed for fundamental and harmonic frequencies of 10 GHz and 20 GHz, respectively. Compared to existing harmonic radar transponders, this transponder is easy to construct because the loop inductor can be implemented with a simple bend in the dipole conductor without degrading performance. Through careful design optimization, the conversion loss of the transponder is not impacted by the measures taken to minimize its mass. The expected harmonic power versus the transmitted power is estimated based on the link analysis between the transmitter and receiver of the radar, with the link analysis itself being performed via calculation, harmonic balance simulation, and full-wave simulation. The link analysis simulation predicted a received power of -66.4 dBm for a transmitted power of +22 dBm and a range of 2.4 m. The measured received power level at the harmonic frequency, obtained from the broadside of the transponder in an anechoic test chamber, is approximately -70 dBm, which agrees well with the link analysis. Simulated and measured transponder radiation patterns are also compared and show good agreement. A transponder with reduced mass compared to previous generations enables the tracking of smaller insects without diminishing their lifespan or undermining their natural flying abilities at various altitudes and ranges. The interplay between power at the fundamental and harmonic frequencies within the transponder depends on the properties of the connected diode. By conducting simulations, the relationship between these powers can be determined and formulated, enabling the optimization of the transponder’s performance. Given the fragile structure of a low mass transponder, it is crucial to assess the impact of transponder deformation on detection performance. The extent of deformation impacts the transponder’s performance, manifesting in both positive and negative effects. However, it is worth noting that the deformed transponder exhibits altered polarization, which has the potential to enhance its performance.