Metal-Only 3-D Unit Cell for Reflectarrays With Independent Dual-Band Operation

This letter presents a metal-only reflectarray based on a 3-D unit cell with dual-band capability. The 3-D unit cell is a square waveguide whose vertical walls include resonator elements with independent frequency performance. Different resonator geometries are analyzed to obtain a reflected phase variation in the target frequency band and to be feasible for 3-D manufacturing. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$C$</tex-math></inline-formula>-shaped and triangle-shaped resonators are selected to obtain the required phase shift in reflection. A reflectarray prototype is designed, including pairs of resonators where the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$C$</tex-math></inline-formula>-shaped resonator controls the low-frequency band, and the triangle-shaped resonators do so for the high-frequency band. The main reflected beam directions for each frequency band are different to show the independent phase tuning of the resonators. The prototype is manufactured using stereolithography with a subsequent silver coating. Measured results show realized gains of 21.2 dBi in the 18 GHz band and 23.63 dBi in the 26.75 GHz band, with a good agreement with the simulated results.