3-D Printed Wideband Cassegrain Antenna With a Concave Subreflector for 5G Millimeter-Wave 2-D Multibeam Applications

A novel wideband planar Cassegrain beam-former with a three-layered folded parallel plate waveguide geometry is investigated. By replacing the convex subreflector of the conventional design with a concave one, a 20% reduction in the size in boresight direction of the planar Cassegrain beam-former can be achieved, while its operating characteristics are not degraded. The direction of the radiation beam can be adjusted independently in the H- or E-plane by laterally offsetting the feed waveguide or bending the waveguide linking with the metallic flare that operates as a radiating structure. By this means, five Cassegrain subarrays with multiple waveguide inputs and different bending angles are stacked to build a high-gain wideband 2-D multibeam antenna array in the Ka-band, whose 3 dB beams cover angular ranges of ±60° in the E-plane and ±18° in the H-plane. A bandwidth of more than 40%, stable multibeam radiation with cross polarization of less than -25 dB, a gain of higher than 20 dBi, and a radiation efficiency of more than 90% are confirmed experimentally by a metallic 3-D printed subarray. With the compact printable geometry and the good operating performance, the presented 2-D multibeam antenna fed by the planar Cassegrain beam-formers is an attractive candidate for millimeter-wave multiple-input multiple-output (MIMO) applications in the fifth-generation (5G) mobile communications.