Additively Manufactured Metal-Only Waveguide-Based Millimeter-Wave Broadband Achromatic Reflectarrays

This communication demonstrates additively manufactured metal-only waveguide-based tri-band and broadband reflectarray antennas. The unit cell (UC) is implemented by cascading two metal waveguide sections with different cut-off frequencies [f(c1) and f(c2) (f(c1) < f(c2))]. When illuminated with the feed antenna, the reflectarray provides different reflection paths to compensate for the spatial phase delay over triple bands, f(l) (f(l) < f(c1)), f(m) (f(c1) < f(m) < f(c2)), and f(h) (f(h) > f(c2)). By tuning the length of the two waveguide sections and vertically adjusting the position of the UC, the phase-shifting over the triple bands can be independently controlled. In addition, because of the sharp selectivity of the waveguide, a reflectarray with the broadband achromatic feature can be achieved by properly selecting the tri-band's frequency and the cut-off frequency of the waveguides. A tri-band reflectarray centering at 25 GHz (low band), 32 GHz (middle-band), and 37 GHz (high-band) is designed first to demonstrate the independent beam shaping over triple bands. Then, two waveguide-based reflectarrays with the broadband achromatic feature are designed, which show stable performance from 22 to 38 GHz with a relative bandwidth of 53.3%. The prototypes are conveniently fabricated using additive manufacturing, and their performance is experimentally verified.