The present disclosure relates to a gradient structure (100) for transmitting and/or reflecting an electromagnetic signal. The gradient structure comprises a plurality of interconnected cells (110). Each cell comprises a through cavity (112) surrounded by walls (111), wherein the walls of each cell have a gradually varying thickness along a longitudinal direction of each cell. The present disclosure also relates to a cover structure (200) comprising the gradient structure (100), a system (300) comprising the cover structure (200), a structure element (400) having integrated therein the system (300) and to a method for optimizing the transmittance and/or reflectance of an electromagnetic signal of a gradient structure.