Low-profile reflective metasurface for broadband OAM beam generation at Ka-band

A low-profile reflective metasurface antenna is designed and fabricated to generate wideband orbital angular momentum (OAM) beams in the Ka-band (27–40 GHz). The design has a reflective phase-shifting element consisting of two diamond loops and two cross-dipoles forming a patch etched onto a dielectric substrate. This configuration achieves a 560° reflection phase range and minimal reflection loss −0.19 dB at 30 GHz, ensuring high-efficiency beam manipulation. The metasurface generates higher-order OAM modes (l=+1,+2,+3,+4) with precise phase control by optimizing the unit cell dimensions. Experimental results demonstrate robust performance for the l=+2 mode, attaining a 43.33% fractional bandwidth, a peak gain of 21.94 dBi, and 12.44% aperture efficiency, an important trade-off for wideband operation. The design's compact profile, linear phase response, and broadband capabilities make it more suitable for high-capacity millimeter-wave communication systems.