A Compact Unit-cell Design for mmWave Reconfigurable Intelligent Surfaces

This paper presents a novel compact unit-cell design for 1-bit reconfigurable intelligent surfaces (RISs) with suppressed quantization lobes. This is achieved by introducing a random pre-phasing over the RIS., utilizing delay lines within the confined space of the unit-cell. To achieve a compact topology with a $\boldsymbol{\lambda/2}$ unit cell periodicity., a triple-layer stack-up topology is presented. As such., the unit cell comprises., a patch antenna., a delay line., a radio-frequency (RF) choke., a Vcc pad., and a PIN diode switch within a $\boldsymbol{5\text{mm}\times 5\text{mm}}$ footprint. We evaluate the proposed unit cell layout with full-wave simulations of a 64-element tile at 28 GHz. The presented RIS topology could be leveraged to extend the signal coverage., increase signal-to-noise ratio (SNR), or improve physical layer security (PLS) in mm Wave 5G and beyond wireless communication systems.