Exploiting the topological robustness of composite vortices in radiation systems

Recent years have witnessed an increasing interest in topological states of condensed matter systems, whose concepts have been also extended to wave phenomena. Especially at optical frequencies, several studies have reported applications of structured light exploiting topological transitions and exceptional points or lines, over which a field property of choice is undefined. Interesting properties of light beams with phase singularities (such as the creation, annihilation or motion of these topological points) have been observed in composite vortices consisting of superimposed light beams with different topological charges. Here, we discuss how these concepts may have a relevant impact on antenna technology at microwave frequencies. We obtain the superposition of vortex fields with different topological charges by simultaneously exciting different modes of a patch antenna. This can be useful to give a physical interpretation for the behavior of some structures, already proposed at microwave frequencies, which use superposition of different radiating modes to manipulate the radiation pattern of patch antennas. Moreover, this approach may open new strategies to design at will the directivity properties of a patch antenna with inherently robust responses, and it may find applications in the design of smart antenna systems, requiring pattern reconfigurability.