Fully Planar 2-D Multibeam Millimeter-Wave Antenna With Via-Based Phase Shifters

For fifth-generation (5G) millimeter-wave (mmWave) beamforming, a fully planar 2 × 2 2-D multibeam antenna operating at 24–28 GHz is proposed. The proposed antenna is fed by a compact dual-layer 4 × 4 Butler matrix in substrate-integrated waveguide (SIW). In this fully planar and compact configuration, SIW coupling slot is used to facilitate the output ports of the Butler matrix on the same planar layer, and the via-based phase shifters are designed to generate wideband phase performance with compact size. The measured impedance bandwidth is 15.4%, and the measured maximum beam pointing angle is 55°. These results are in good agreement with simulation. The proposed configuration can be extended with more radiating elements for higher gain, and it is promising for beamforming scenarios, including communications.