A UHF 1.3 cm2 Passive Subharmonic Tag With a 13 m Read-Range

This work reports on the design and performance of the first single-antenna subharmonic tag (SA-SubHT) of its kind. Thanks to the high-quality factor of its planar electrically small antenna (ESA) and to the advantageous nonlinear dynamics enabled by the adoption of two nonlinear components in its circuit, the reported SA- SubHT exhibits an exceptionally low-power threshold (
$P_{\text {th}}$
= −18 dBm). Such a low
$P_{\text {th}}$
-value is achieved regardless of the extraordinarily small size of the reported SA- SubHT (its area is only 1.3 cm2), which has been built onto a 12.4
$\times $
10.6
$\times $
1.6 mm3 FR-4 printed circuit board (PCB) and uses a ultrahigh-frequency (UHF) ESA occupying just 78 mm2. When using an effective isotropic radiated power (EIRP) at 890 MHz of +36 dBm for its interrogation in an uncontrolled electromagnetic environment, the reported two-varactor SA- SubHT generates a subharmonic response at 445 MHz detectable from more than 13 m away from its interrogating device. This read-range exceeds by more than three times the distance the same SA- SubHT on an identical PCB covers when the second varactor is replaced by an equivalent linear capacitor with a nominal capacitance identical to the varactor’s zero-bias capacitance. The reported SA- SubHT creates new exciting possibilities to implement a fine-grained remote sensing through the deployment of a large number of SA- SubHTs.