Millimeter‐Wave Beamforming Networks

A beamforming network (BFN) is a physical layer element of an array system that combines signals with the requisite amplitudes and phases required to produce a desired angular distribution of emitted radiation, i.e., one or more beams pointed in prescribed directions. The most popular circuit‐type BFN is the Butler matrix (BM). Circuit type BFNs are suited to microwave and lower millimeter‐wave (mm‐wave) bands. Three popular quasi‐optical‐type BFNs are Luneburg lens, Rotman lens, and reflectors. This chapter briefly reviews the recent development of mm‐wave substrate integrated waveguide (SIW) based BFNs, including those associated with circuit‐type and quasi‐optics‐type BFNs. A BFN based on a BM feeds an array in a parallel fashion. In contrast, one based on a Nolen matrix feeds it in a serial fashion. With the development of 5G communications, mm‐wave SIW BFNs have attracted more and more attention. They have the advantage of compact size, low insertion loss, and ease of fabrication.