Hexagonal Pixels Facilitating Topological Design of 2-bit 2-switch Phase-Reconfigurable Unit Cells

RF-switch-enabled phase-reconfigurable unit cells are the key building blocks for low-cost reconfigurable intelligent surfaces and beam steerable reflect-/transmit-arrays. Most of the existing multi-bit unit cell designs do not exploit all the possible switch combinations and thus achieve less phase resolution than the switches can potentially offer. In this work, we apply binary particle swarm optimization to design pixelized unit cell elements such that the maximum number of phase states can be realized for a given number of switches. As an example, the design of 2-bit, 2-switch reflectarray unit cells for 18.5 – 19.5 GHz is presented. Hexagonal pixel is introduced as the basic geometry, which leads to better unit cell performance and faster optimization convergence than conventional square pixel.