2-D Orthogonal Multibeam Antenna Arrays for 5G Millimeter-Wave Applications

Abstract

In this article, a 2-D <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16 \times 16$ </tex-math></inline-formula> Butler matrix-based passive multibeam antenna array (MBAA) and a 2-D active–passive hybrid MBAA (APHMBAA) are both presented for fifth-generation (5G) millimeter-wave (mmWave) applications, which demonstrate that a 2-D coverage can be achieved by two types of 1-D beamformers in two orthogonal planes at analog beamforming level. For the 2-D passive MBAA (PMBAA), the 16 beams are controlled by two stages of substrate integrated waveguide (SIW) Butler matrices placed orthogonally. A novel 2-D interconnection method for connecting these two-stage Butler matrices is implemented based on the flexibility of the SIW without any connectors, cables, and soldering operations and then possesses the advantages of low cost, extensible, and integrated easily in the mmWave bands. The measured results exhibit that the operating bandwidth is 15.38% for the single-stage Butler matrix-based antenna array. Meanwhile, the maximal beam gain of the 2-D PMBAA is 9.4 dBi and its accurate beam directivity is also observed. For the 2-D APHMBAA, the multiple beams are generated by the Butler matrix-based passive beamformers in the vertical direction, whereas the beamforming on the horizontal direction is realized by the active networks utilizing mmWave active beamformer chips. Compared to the proposed 2-D PMBAA, the horizontal scanning performance of the hybrid framework is more flexible. What is more, its costs and complexity are both reduced tempestuously in comparison with an active multibeam array. The measured results show that the maximum measured beam gain of the array is 10.9 dBi and the chip channel gain is 27 dB. A wide 2-D spatial angle is covered simultaneously by the proposed hybrid beamforming scheme.