Spiraphase-Type Reflectarray for Large Reflection Elevation Angles

This paper presents a spiraphase-type reflectarray based on reactively loaded ring slot resonators. The infinite array approach was used to optimize the unit cell geometry to obtain high aperture efficiencies and low cross-polarization levels at large reflection elevation angles θ_o. The results of the optimization were used to design four 367-element reflectarrays for θ_o of 0°, 20°, 40°, and 60° operating at 36.5 GHz. The designed reflectarrays were then fabricated and tested. The experimental investigation of the fabricated reflectarrays revealed that aperture efficiencies of 0.60, 0.51, 0.42, and 0.21 along with cross-polarization levels of -25.8, -24.0, -17.8, and -10.9 dB were obtained for the reflectarrays with reflection elevation angles of 0°, 20°, 40°, and 60°, respectively, at 36.5 GHz. Additionally, it was experimentally demonstrated that for certain planes of scanning the cross-polarization level can be reduced to -19 dB even for reflection elevation angles θ_o as high as 60°.