Compact Green Harmonic Transponders for Parcel Tracking

This article presents a harmonic transponder, designed to minimize the tag sensitivity to the materials close to it. The tag is based on a dual-frequency dual-port patch antenna and a frequency doubler. The tag is designed to be interrogated by the fundamental frequency $f_{0}$ equal to 2.4 GHz and it backscatters a signal at $2f_{0}=4.8$ GHz. The patch is realized on cardboard, while the frequency doubler and the feedlines are manufactured on a flexible polylactic acid (PLA) substrate. The feed lines are electromagnetically coupled to the patch through H slot apertures. A complete prototype with an area occupation of $5\times 10$ cm ² was manufactured and directly integrated in a parcel. The antenna features a front-to-back ratio higher than 12 dB at both operating frequencies. The tag could be read up to a distance of 6 m with a transmitted power of 25 dBm Equivalent Isotropically Radiated Power (EIRP), regardless of the object placed in the parcel close to the tag. This work opens the door to a new class of harmonic transponders for tracking applications, characterized by low environmental impact, high integrability, compactness and reliability, which can find application in many Internet of Things emerging applications.