Marvin Joshi, Charles A. Lynch, Kexin Hu, Genaro Soto-Valle, Yaw A. Mensah, John D. Cressler, Manos M. Tentzeris
The rapid expansion of next-generation Internet-of-Things (IoT) infrastructures demands scalable, battery-free sensing systems capable of accurate long-range detection, motivating the shift from battery-powered devices to fully passive architectures. This work presents a lens-enabled, fully passive harmonic millimeter-wave identification (mmID) system that unites wide-area coverage with precise localization. The design integrates a cross-polarized dual-band antenna, a zero-bias frequency doubler, and a low-loss polytetrafluoroethylene (PTFE) dielectric lens, with lens geometry synthesized through ray tracing at fundamental and harmonic frequencies to ensure focal stability for incidence angles up to$\pm {\mathrm {55~\!{^{\circ}}}}$. The Schottky diode frequency doubler was rigorously modeled through current–voltage (I–V) fitting and through–reflect–line (TRL) deembedding to extract an accurate equivalent circuit. The complete mmID achieves a peak harmonic radar cross section (RCS) of$\mathrm {-29.1~\text{dBsm} }$and −10 dB angular coverage across$\pm {\mathrm {55~ {^{\circ}}}}$, corresponding to a 2.679-sr solid angle. In localization tests with a proof-of-concept (PoC) reader, the retrodirective harmonic mmID delivered mean ranging errors below 4 cm up to 82.5 m and submillimeter accuracy using phase-based tracking within 25 m, while link budget analysis projects maximum ranges of 1.5 km at boresight and 1.2 km at$\pm {\mathrm {55~ {^{\circ}}}}$. By combining passive operation, wide angular coverage, and long-range precision, the proposed harmonic mmID provides a scalable, low-maintenance platform for emerging 5G/millimeter-wave (mmWave) cyber-physical systems (CPS) and IoT environments.