2.75-Bit Reflecting Unit Cell Design for Reconfigurable Intelligent Surfaces

This work proposes a phase-shifting unit cell for a reconfigurable intelligent surface capable of exhibiting 8 discrete phase states at 5G mid-band. An individually addressable unit cell embedded with 3 PIN diodes has been designed to provide enhanced phase resolution with a minimal number of active components. A particle swarm optimisation algorithm has been employed in order to maximise the phase state separation whilst minimising reflection loss and unit cell periodicity. Simulations are performed with extracted PIN diode and capacitor Sparameters for a realistic estimation of the fabricated device performance, with a resulting simulated average reflection loss of 1 dB and equivalent phase resolution of 2.75-bits.