To address wireless service requirements for 5G/6G connectivity, there is an increasing focus on millimeter-wave (mmWave) technologies. As is well-known, mmWaves are severely affected by propagation and scattering mechanisms that are associated with increased attenuation and signal blockage. While Multiple-Input Multiple-Output (MIMO) approaches can mitigate some of these issues, there are associated costs related to hardware, power consumption, and signal processing complexities. Alternatively, Reconfigurable Intelligent Surfaces (RIS) provide for a cost-effective alternative in realizing higher network throughput. RIS surfaces are comprised of three main layers. The first layer consists of a periodic set of reflective cells whose surface impedance varies across the RIS surface using phase control circuits on the back end (2nd RIS layers). A potential third layer comprises the digital control of the reflective circuits via PIN diodes, MEMs or varactors diodes. This RIS third layer allows for phase control configuration to maximizes power delivery along specific directions.
