Enabling Broadbeam Performance in Planar Backscatter Tags: A Semi-Passive Metalens-Enhanced mmID for Ambient IoT Environments

For the first time, a planar metalens-enabled semi-passive mmWave identification (mmID) system is demonstrated, achieving high detectability, wide angular coverage, and ultra-long-range operation in an ultra-compact form factor. The design integrates an ultra-thin Huygens metalens with a cross-polarized aperture-coupled stacked patch array to enable low-loss transmission and efficient backscatter. The metalens provides stable focusing and retrodirective behavior across 26 –29 GHz, achieving a peak differential RCS of −13.1 dBsm and a −10 dB angular coverage of ±55°. Outdoor measurements confirm reliable detection up to 200 m at both boresight and 55° incidence, closely matching theoretical predictions. Link-budget projections further indicate reading ranges of up to 9.8 km under the 75 dBm EIRP permitted in 5G/mmWave systems. With its compact form factor and wide angular coverage, the proposed mmID enables a new class of devices for next-generation ambient IoT and digital-twin networks.