Broadband Operation of Binary Metasurfaces: Limitations and Perspectives

In this paper, physical prerequisites of the broadband operation of reflective intelligent surfaces (RIS) implemented as periodically non-uniform metasurfaces (MSs) of binary type are elucidated. The general relation for the maximal operational band of a binary MS following from these prerequisites is deduced. Based on this relation, the general rules for engineering the periodical RISs based on the binary MSs with the maximally broad frequency band are formulated. Recent studies in which this maximum was approached are discussed. Finally, we present a numerical example of an original binary MS designed with these guidelines which grants for restricted incidence angles an ultra-broadband operation.