Planar Beamforming Networks for Producing Multiple Independently Steerable Beams

This paper presents a design of multibeam beamforming networks (BFNs) using planar microstrip circuit. The multibeam BFNs, which are based on the generalized joined coupler matrices, can produce multiple independently steerable beams using one feed network. Key to the BFN design is a mixture of one-section and two-section branch-line couplers, which are able to realize a wide range of coupling coefficients. The theoretical analysis on a 3 × 8 is conducted first, and then an electromagnetic model is designed and simulated using microstrip lines. Finally, the BFN is fabricated, tested, and employed to feed an 8-element linear array, demonstrating its capability of producing three steerable beams.