On the Radiation of Curved Beams in the Near-Field by Distributed Caustics for NLOS Applications

This paper introduces a novel method for synthesizing focused and curved electromagnetic beams in the near-field region, targeting high-frequency applications in the microwave and millimeter-wave domains. The approach leverages ray–caustic theory, which models beam propagation using high-frequency ray approximations, where caustics can be interpreted as geometrical loci of localized field enhancement caused by the envelope of rays. By defining the desired beam trajectory through a target caustic curve, the method enables spatial control of the field distribution along arbitrarily shaped paths. In contrast to other more conventional techniques based on non-diffractive beams, the proposed method offers enhanced flexibility in beam trajectory shaping, making it suitable for applications that require strong field confinement and accurate beam steering in the near field. These include short-range wireless power transfer, chip-to-chip communications, and near-field imaging. The effectiveness of the technique is proven by a simple analytical model, validated through full-wave simulations by CST Microwave Studio. Moreover, a realistic implementation of curved beam launchers is presented, based on a slot array in a parallel-plate waveguide. The results confirm the method ability to radiate near-field beams that closely follow the designed spatial trajectories, thus opening new potential applications for advanced near-field control in high-frequency systems.