Flexible Manipulation of Emitting Beams Using Single-Aperture Circularly Polarized Digital Metasurface Antennas: Multi-Beam Radiation toward Vortex-Beam Generation

As the technological demands for multiple-input multiple-output communication systems increasingly grow, there is a critical need for the next generation of multi-beam radiators. The concept of single-feed compact phase-encoded metasurface antennas is introduced, the radiation specifications of which can be flexibly manipulated to provide circularly-polarized single-, dual-, quad-beam far-field patterns, a circularly-polarized optical angular momentum-carrying beam, and a circularly-polarized quasi-omnidirectional emission. With a small footprint area at f = 5.8 GHz, the proposed circularly polarized coding metasurface antenna (CPCMA) consists of several radiating meta-atoms with 2-bit excitation phases of 0, pi/2, pi, and 3 pi/2. Compared with conventional antenna arrays, the center-to-center distance of the coding elements is noticeably reduced, where periodic boundary conditions have been employed to analyze the inter-element coupling effects. A low-cost and simple corporate feed network is also designed to implement the required coding mask of each CPCMA type. To verify the performance of the proposed CPCMA, a prototype is fabricated and measured. Proof-of-concept experiments demonstrate excellent agreement with numerical simulations and theoretical predictions. This constructs a bridge between conventional arrays and digital metasurfaces, providing a powerful host for the next generation of multi-beam circularly polarized radiators.