2D periodic structure featuring negative group velocity of bloch waves

A 2D, volumetric (i.e., non-planar), structure consisting of two dielectric layers, loaded by various metal inclusions on multiple-periodic grids and closed by two confining metal planes is introduced in view of advanced dispersion engineering related applications. Full-wave simulation has been used to demonstrate that, for axial propagation, the structure presents (i) a large electromagnetic band-gap and (ii) two modes that have anti-parallel phase and group velocities in different frequency bands where they do not interact with other modes.