Broadband Metasurfaces through First Order Approximation of Surface Impedances

We introduce a method of bandwidth enhancement on metasurfaces based on a more insightful analytical approach of LC resonances. In obtaining L and C parameters, we use surface impedance model considering not only a single frequency matching but also its first frequency derivative. We show that broadband anomalous reflection can be obtain with simple geometries involving dipole and inverse dipole structures. We verified our method using experiment in millimeter-wave frequencies and show that the broadband metasurface achieves a significant increase of bandwidth (more than 80% increase) compared to a single frequency design, with minimum -3dB power is maintained in the desired reflection and maximum -10dB for all other diffraction orders.