An approach to producing the orbital angular momentum (OAM) based on spoof localized surface plasmons (spoof LSPs) in microwave frequencies is demonstrated both theoretically and experimentally. The fundamental and high-order modes of spoof LSPs occur when a textured metallic surface is excited with a microstrip line. Two orthogonal modes of spoof LSPs with +90° or −90° phase retardation are superimposed, resulting in a OAM-vortex mode. In the proposed design, two separate feeding ports are employed to excite the orthogonal resonant modes simultaneously, and a hybrid coupler is used to provide the required ±90° phase retardation. By loading a circularly arranged dipole array on the spoof LSPs, the confined surface waves of the spoof LSPs can be converted into radiated vortex waves. To verify this idea, an OAM-mode emitter with indices of ±3 is fabricated and measured. Experimental near-field distributions and far-field radiation patterns show excellent agreement with the simulated results.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics