Joint communication and sensing with structured beams carrying orbital angular momentum.

Electromagnetic beams carrying orbital angular momentum (OAM) exhibit helical phase structures and doughnut-shaped intensity profiles, offering a promising basis for mode-division multiplexing and for fine-grained sensing in millimeter wave and sub-terahertz regimes. The simultaneous use of multiple OAM modes in joint communication and sensing systems has nevertheless remained unexplored due to conflicting requirements. While concurrent transmission of multiple orthogonal modes maximizes throughput in favor of communication, sensing relies on obtaining location-dependent scattering signatures by probing individual modes. In this work, we exploit the flexibility of OAM multiplexing to reconcile these requirements, based on the core insight that communication capacity depends primarily on the number of active modes, rather than the specific mode indices. Hence, by reconfiguring subsets of OAM modes, we generate diverse composite field distributions, whose reflections from sensing targets encode rich spatial information, while maintaining orthogonality for data multiplexing. We derive the theoretical limits of joint sensing performance and validate our approach through extensive over-the-air experiments at 120 GHz, demonstrating accurate target localization alongside high-speed data transmission. Our modeling and design are built on a deep understanding of the physics of OAM-carrying beams and the fundamentals of multiple-input multiple-output wireless propagation channels.