Cascaded-Metasurface-Enabled Bessel Beam with Continuously Tunable Depth of Field

This paper introduces a Moiré cascaded metasurface (MCM) antenna designed to launch steerable Bessel beams with a continuously tunable depth of field (DoF). The antenna consists of two closely placed metasurfaces illuminated by spherical waves from a feed horn. Conjugate phase profiles, inspired by the Moiré effect, are engineered on the two metasurfaces that can be rotated relative to each other to adjust the DoF and axicon angle properties of the Bessel beam. Additionally, stable Bessel beam scanning within a ±30° range is obtained by mechanically repositioning the feed horn. By combining in-plane rotation and feed movement, the proposed MCM antenna can generate Bessel beams with controllable non-diffractive regions in 3D space. The concept is further extended to a tri-layer metasurface topology, enabling a more linear DoF control. A prototype of the dual-layer MCM antenna, operating at 10 GHz, is fabricated and tested. Numerical simulations predict a continuously tunable DoF ranging from 110 mm to 950 mm, while experimental results demonstrate a range from 180 mm to 860 mm. The developed MCM antenna, offering 3D-controllable non-diffractive beam shaping, holds promise for applications in imaging, short-range communications, and wireless power transfer.