This paper presents a metal-only reflectarray based on a 3D unit cell with dual-band capability. The 3D 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. C-shaped, triangle-shaped, and circle-shaped resonators are selected to obtain the required phase shift in reflection. A reflectarray (RA) prototype is designed, including pairs of resonators where the C-shaped resonator controls the low-frequency band, and the triangle 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 (SLA) 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.
