A Low-Profile, Broadband, Beam Steerable Folded Reflectarray Antenna for Millimeter-Wave Applications

This letter presents a wideband, low-cost, and low-profile circularly polarized (CP) beam steerable folded reflectarray antenna (FRA) operating in the millimeter-wave (MMW) band. Inspired by the Risley prism concept, the 2-D beam steering function is realized by rotating two beam deflection metasurfaces of the FRA. Moreover, the ray tracing principle is applied to the dual-metasurface structure to reduce the antenna profile. Both metasurfaces have the same phase gradient for beam deflection. The first metasurface also enables the control of transmission and reflection wavefronts based on CP states, while the second source-integrated reflective metasurface converts the incoming CP waves into orthogonal polarization. By controlling the reflection phase distributions, the incident waves undergo anomalous reflections between the two metasurfaces. These anomalous reflections significantly reduce the antenna's profile to 1/4 of the focal length. A prototype antenna operating at 60 GHz was designed, modeled, and experimentally verified, agreeing well with the theoretical estimation, demonstrating that the FRA shows a wide scanning range of 0° ∼ 40°. For broadside radiation, the fabricated FRA achieves a realized gain of 22.4 dBic at 60 GHz and a 3-dB gain bandwidth of 18.8% in the measurement.