Uniplanar Beam-Forming Network Employing Eight-Port Hybrid Couplers and Crossovers for 2-D Multibeam Array Antennas

A multibeam beam-forming network (BFN) for generating 2-D multibeam array antenna (MAA) is proposed using single-layer substrate integrated waveguide (SIW) technology. Firstly, a new topology for building 16 x 16 BFNs is proposed, which successfully transforms the traditional topology from a 3-D configuration to a 2-D (or uniplanar) one. Two major challenges are tackled during this transformation, namely, the planarization of basic components and the reduction of excessive intersections between multiple paths. To this end, a novel design of eight-port hybrid couplers, as critical components of this BFN, is developed to transform a 3-D to a 2-D structure. Furthermore, a new design of eight-port crossover, which can address four path intersections simultaneously, is proposed to reduce the total number of path intersections from 16 to only 4. The proposed topology for 16 x 16 BFNs allows all the basic components, including eight-port hybrid couplers, eight-port crossovers, and phase shifters, to be placed within a single-layer configuration. Fed by the proposed uniplanar 16 x 16 BFN, a 2-D MAA with 16 (4 x 4) beams, which is capable of switching the beams in both elevation and azimuth directions, is realized. Compared with the previous 2-D Butler matrix (BM) designs using multilayer technology, it is for the first time that a uniplanar design of 16 x 16 BFN is proposed and realized, which significantly simplifies the design and fabrication complexity.