Synthesis Method of an Orthogonal Beamforming Network With Arbitrary Ports for Shaped Beams

This article proposes a synthesis method of orthogonal beamforming networks (BFNs) with arbitrary ports. The proposed method is based on matrix decomposition theory and breakthrough the synthesized BFN number to arbitrary. It has been theoretically demonstrated that the BFN with cascading 180° hybrid couplers can synthesize shaped beams. Therefore, a BFN synthesis method that combines the QR decomposition theory and the optimization algorithm is introduced. With the help of an optimization program, a specific power ratio of each 180° hybrid coupler in the BFN is determined. The proposed synthesis method is verified by experiments with an orthogonal 6×2 BFN with flat-topped radiation patterns. Through optimization, five 180° hybrid couplers with different power ratios synthesize the proposed BFN. Results show that two flat-topped beams with a beamwidth of (32° ± 0.3°), gain ripples less than 2.5 dB, and a sidelobe level less than 12 dB are achieved. The proposed method has the advantages of high accuracy and efficiency and a simple structure, which makes it convenient for multi-beam antenna arrays in multiple-input-multiple-output (MIMO) systems.