Unit Cell Design in Reconfigurable Intelligent Surface Array in Beam-Steering Applications

A Reconfigurable Intelligent Surface (RIS) is a programmable surface structure used to control the electric and magnetic properties of reflected signals. It controls the reflected signal characteristics, such as polarization and phase, dynamically. The strategic placement of RIS in the wireless channel between transmitter and receiver enhances the link quality by steering the reflected signals towards the receiver. RIS can be implemented either using antenna arrays or metasurfaces. In this paper, an antenna arrays based RIS design approach is followed, and a reconfigurable 'unit cell' is designed using rectangular microstrip patch antennas at 26 GHz frequency for beam-steering applications. Unit cells with 6.7 mm × 7.5 mm dimensions, coupled with variable slot lengths, yield a comprehensive range of phase variations. PIN diodes were selected as the reconfiguration elements due to their rapid switching capabilities and relatively low insertion loss at the target frequency of 26 GHz. A careful alteration of unit cell geometry and strategic placement of tuning elements on the resonating patch are proposed. Its behaviour is examined when reconfigurable unit cells are arranged as an array structure.