Tapered All-Dielectric EBGs with 3-D Additive Manufacturing for High-Gain Resonant-Cavity Antennas

A resonant-cavity antenna is implemented assembling on an open-ended rectangular waveguide a wideband electromagnetic band gap (EBG), designed as a multilayer. Two different implementations of the multilayer are proposed, labeled as Cases A and B. As to Case A, a high-permittivity layer is embedded between two slabs of low permittivity, whereas a single layer of low permittivity, surrounded by two high-permittivity slabs, is employed in Case B. Successful performances of the broadband behavior are also dependent on the side length of the EBG, that is truncated to small footprints, with an effect of high sidelobe level (SLL). Therefore, grid layouts with nonuniform air holes are proposed for in-plane realization of the dielectric slabs. Their effect in the EBG superstrate is a nonuniform spatial reflectivity, that reduces the SLL keeping a good wideband response. In the EBG manufacturing, both numerically controlled machining techniques and 3-D printing have been employed. 3-D printing has been used for the low permittivity layers, realized in the polylactic acid (PLA) filament, allowing more flexibility in the fabrication of the grid slabs to custom layouts. Results of two antenna prototypes assembling the EBGs, with the parameters of Cases-A and -B and grid layout, to the waveguide source are reported.