Enabling a >13 m Reading Range Through Passive Single-AntennaSubharmonic Tags Occupying Less Than 1.3 cm^2

This work reports on the design and performance of the first single-antenna Subharmonic tag (SA-SubHT). Thanks to the high quality factor of its planar electrically small antenna and to its advantageous nonlinear dynamics enabled by the adoption of two nonlinear components in its circuit, the reported SA-SubHT exhibits an exceptionally low power threshold Pth = -18.6 dBm). Such a low Pth-value is achieved regardless of the extraordinarily small size of the reported SA-SubHT (total area of only 1.3 cm^2). When using an EIRP at 890 MHz of +36 dBm for its interrogation in an uncontrolled electromagnetic environment, the reported SA-SubHT generates a subharmonic response at 445 MHz detectable from more than 13 meters away from the interrogator, far exceeding the distance the same SA-SubHT covers when only one varactor is used. The reported SA-SubHT creates new possibilities to implement a fine-grained remote sensing through the deployment of many SA-SubHTs.