2-Bit Phase Quantization Using Mixed Polarization-Rotation/Non-Polarization- Rotation Reflection Modes for Beam-Steerable Reflectarrays

We present a new method for achieving 2-bit phase quantization for beam-steerable reflectarrays by exploiting four distinct reflection modes of a unit cell. Two of the four modes perform polarization-rotation (PR) operation while the other two are non-PR modes when the unit cell is illuminated by an x- or y-polarized incident wave. With a specific phase relation between the four reflection modes, the unit cell acts as a 2-bit phase shifter under illumination with an incident wave polarized along a diagonal direction of the square-shaped unit cell. The proposed operating principle was demonstrated with an illustrative unit cell consisting of three metallic layers and using four single-junction connections that can be replaced with single-pole single-throw (SPST) switches for reconfiguration. Simulation results predict an operating bandwidth of about 20% for the unit cell and a good beam scanning performance over a scan range of ±45° for a beam-steerable reflectarray constructed using this unit cell. Two static prototypes of the beam-steerable reflectarray antenna providing beam collimation at two different directions at 10 GHz were fabricated and experimentally characterized. Measurement results show good agreement with the simulation results, validating the proposed design approach for 2-bit reflective unit cells.