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 [
$\text{f}_{\mathrm {c1}}$
and
$\text{f}_{\mathrm {c2}}$
(
$\text{f}_{\mathrm {c1}} < \text{f}_{\mathrm {c2}}$
)]. When illuminated with the feed antenna, the reflectarray provides different reflection paths to compensate for the spatial phase delay over triple bands,
$\text{f}_{l}$
(
$\text{f}_{l} < \text{f}_{\mathrm {c1}}$
),
$\text{f}_{m}$
(
$\text{f}_{\mathrm {c1}} < \text{f}_{m} < \text{f}_{\mathrm {c2}}$
), and
$\text{f}_{h}$
(
$\text{f}_{h} > \text{f}_{\mathrm {c2}}$
). 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.