Printed Dual-Layer Three-Way Directional Coupler Utilized as 3 $,\times,$ 3 Beamforming Network for Orthogonal Three-Beam Antenna Array

We present a novel printed dual-layer three-way directional coupler, which can be utilized as 3 × 3 beamforming network (BFN) to provide orthogonal three-beam switching capability. The three-way directional coupler is a passive component with six input/output ports. The signal injected into the input port is equally distributed into the three output ports, with a constant phase difference of -120 ^°, 0 ^°, or +120 ^°. Simulation and measurement results show that within 7% relative bandwidth, good matching, high isolation, equal power division, and constant phase difference have been achieved simultaneously. Utilizing the three-way directional coupler as a 3 × 3 BFN, an orthogonal three-beam antenna array for 5.8-GHz application has been designed, fabricated, and tested to verify its capability experimentally.