Reconfigurable Harmonic RF Transponder for Proximity Detection

Abstract

Proximity detection systems have witnessed a remarkable growth in interest in the past years. In fact, particularly with the COVID-19 outbreak, social distancing in public areas and workplaces has become a norm, and human proximity monitoring became a challenge. Moreover, applications of detection systems extend beyond maintaining physical distance between individuals and can be integrated in industrial fields for products localizations and identifications. Hence, sensing systems with desirable characteristics, such as high reliability, low cost, compact size, and ultralow power consumption, are highly demanded. Harmonic radars and transponder-based sensing systems are attractive candidates to resolve such challenges. In this concept, a transponder is interrogated by a radar at the fundamental frequency f0. The transponder attached to the target then reflects a higher harmonic, which can be detected by the radar system. Such transponders are realized at the second-harmonic frequency 2f0 in most cases. The received signal from the transponder can be used to estimate the distance between the radar and the transponder attached to the object. In this thesis, a novel diplexer-based and frequency reconfigurable harmonic transponder is presented. Unlike traditional transponder architectures with two separate antennas, the integration of a diplexer allows the transponder to simply employ a dual band antenna shared by both the transmitter and the receiver. By loading the diplexer with external capacitors, its fundamental and harmonic frequencies reduce from 5 and 10 GHz to 2.5 and 5 GHz respectively. The validity of the proposed transponder is investigated experimentally using a directional coupler where measurement results agree significantly with predicted data.