Tapered EBG superstrates for low-permittivity resonator antennas

High-gain antennas can be implemented applying an EBG structure as superstrate to planar low-gain radiators. A cavity is formed between the ground plane backing the primary source and the EBG superstrate, that is realized with a low-permittivity dielectric, in order to be fabricated with a 3D printer. Due to the finite size of the EBG layers, diffracted fields occur at the edges of the cavity. Furthermore, notwithstanding the considerable gain enhancement, most times side-lobe level is not optimized. EBG layouts with tapered periodicity are proposed to control the reflectivity of the EBG superstrates from the center of the structure towards the edges, in order to reduce diffraction effects and lower the side-lobe level.