A Novel Hybrid Analog-Digital Multibeam Antenna Array for Massive MIMO Applications

In this paper, a novel hybrid analog-digital multibeam antenna array is proposed for massive multiple-input multiple-output (MIMO) application. Passive multibeam antennas fed by analog beamforming networks are used for handling multiple beams in the elevation plane simultaneous. The radiation beam steers horizontally by arranging the passive multibeam antennas in the azimuth plane and shifting the signal phases in a digital beamformer. Because of the implementing of a passive beamformer network, a large number of antenna elements are employed by less channels. The digital beamforming (DBF) processing is simplified the power consumption can be decreased. To verify the concept, a $4x8$ modified Butler matrix is adopted and implemented in the substrate integrated waveguide (SIW) form with the 13.45% bandwidth at 26 GHz. An 8-beam antenna consists of two tapered slot antenna (TSA) arrays fed by the Butler matrixes which inclines ±5.5 orespectively to achieve high beam crossing levels and enlarge the scan coverage. Then, a 128-channel hybrid analog-digital multibeam receiver array module is fabricated by arranging 168-beam antennas. The measured results show that the scan coverage larger than $\pm 45 \circ $ in both azimuth and elevation planes. The performance of the proposed architecture is excellent and it presents an excellent candidate for 5G communication systems.