3D Additive Manufacturing of Tapered EBG Layers for a Resonant-Cavity Antenna

3D Fusion Deposition Modelling (FDM) technique is applied, in combination with numerical machining technique, to the fabrication of an Electromagnetic Band-Gap (EBG) multilayer used as superstrate of a Resonant Cavity Antenna (RCA). The primary source of the RCA is a rectangular waveguide WR90 in the X-band, and it is backed by a metallic plate, to form a cavity with the EBG placed above, which behaves as a partially reflecting surface. The EBG superstate is designed alternating three dielectric and planar layers, through materials with a permittivity contrast, i.e., by alternating layers having a high permittivity to a layer with low permittivity. This scheme gives to the EBG material a broadband response. In the in-plane design, each layer is shaped as a tapered grid of rectangular holes, to reduce the field scattered at the edge of the cavities, and thus lowering the Side Lobe Level in the antenna radiation patterns. The fabrication of the low-permittivity layer has been performed with additive manufacturing, through a PLA filament which has a relative permittivity of 2.76. The choice of PLA over ABS filament as printing material has been dictated by the different handling of the inner parts of the fabricated samples by the 3D printer. The high-permittivity layers of the superstate, instead, are fabricated from pre-formed vetronite layers, shaping the grid layout through numerically controlled machining technique. The antenna prototype has been measured in anechoic chamber, and experimental results are in very good agreement with the numerical simulations.