Local and Nonlocal Wire-Grid Metasurface Stacks for Spatial and Frequency Filtering

Devices filtering out electromagnetic waves with respect to the direction of propagation or the operating frequency, called spatial (angular) filters and frequency filters respectively, are of interest for numerous applications in a wide range of frequencies. Here, angular and frequency filters composed of stacks of uniform periodic metasurfaces (MSs) are designed for transverse electric (TE) and transverse magnetic (TM) polarizations. Generalized sheet transition conditions (GSTCs) are utilized to characterize each constituent MS separately and the whole structure is semi-analytically characterized using the well-known transfer matrix method (TMM). This approach shows that the proposed filters can be spatially dispersive in general. By adjusting the geometrical parameters of the MS stacks it is shown that various filtering features like low-pass, bandpass, and high-pass behaviors can be obtained. Subsequently, applications of these structures are demonstrated in filtering out the lobes of phased arrays. In addition, tunable high-quality factor resonances and wave phenomena similar to Fano resonances and electromagnetically induced transparency (EIT) are illustrated and discussed.