Full-Space Active Folded Antenna for Versatile OAM Generation and Multi-Domain Communication

This paper presents a novel full-space multifunctional active metasurface. By controlling the switching states of embedded diodes, the proposed metasurface supports five distinct operational modes. Leveraging diverse polarized grids, two advanced active folded antennas (AFAs) are developed for orbital angular momentum (OAM) generation. The first design, AFA-I, operates in transmission, reflection, and transmission-reflection-integrated modes, generating x-polarized OAM beams. Similarly, AFA-II exhibits the same functionalities but generates y-polarized OAM beams. Both AFAs were extensively simulated, fabricated, and experimentally validated. The simulation and measurement results confirm that the generated OAM beams exhibit high mode purity (exceeding 74%) and excellent modal orthogonality. Furthermore, this work presents the first experimental demonstration of an OAM wireless communication system utilizing folded-structure antennas. The system employs quadrature phase-shift keying (QPSK) modulation across multiple OAM communication channels in distinct spatial domains, verifying the orthogonality of different OAM modes. The measured bit error rate (BER) remains below 3.8 × 10⁻³ when the transmitting and receiving OAM modes are matched and exceeds this threshold when they are mismatched. This work overcomes the conventional limitation of single operational space in active folded antennas and experimentally validates the feasibility of full-space, multifunctional active folded antennas for OAM-based wireless communication.