A Miniaturized Broadband 1-Bit Coding Reconfigurable Intelligent Surface for NLOS UE Localization and Uplink Communication

Researchers from IIIT Delhi and NIT Rourkela have unveiled a miniaturized broadband 1-bit coding reconfigurable intelligent surface (RIS) that tackles two critical challenges in wireless communications: non-line of sight (NLOS) user equipment (UE) localization and reliable uplink communication. The metasurface unit cell is built around a wide dipole modified with interdigital capacitors and loaded with an SMP 1340-040LF PIN diode, enabling cell miniaturization and a stable angular response. It delivers a consistent 180° ± 30° phase difference between ON and OFF states across 4.85–6.05 GHz for normal incidence of TE polarized waves, with reflection loss under 3 dB and a phase difference of 180° ± 50° for oblique incidence up to 45°. RF and DC paths are isolated using butterfly-shaped radial stubs on the bias lines.

A 16×10 element prototype was constructed and paired with a low-cost microcontroller-based control circuit for biasing the PIN diodes. Experimental validation inside an anechoic chamber confirmed the theoretically calculated and full-wave simulated radiation patterns. The team then demonstrated the RIS's capability in an LTE communication framework, showing robust NLOS UE localization and uplink communication. This breakthrough has immediate implications for UAV localization and extended-range uplink in challenging environments, offering a practical path to smarter, more resilient wireless networks without expensive infrastructure upgrades.