In mobile communications such as 5G and 6G, traffic volume is expected to continue to increase. To provide a comfortable mobile communication environment, high-speed, low-latency, high-capacity communication is achieved using high-frequency bands such as the quasi-millimeter wave band. To address the high transmission loss and limited communication area in the high-frequency band, Massive MIMO (Multiple Input Multiple Output) using high-gain array antennas has been introduced. However, this configuration increases the antenna size and signal processing circuits, leading to increased base station footprint and power consumption. One way to solve this problem is to use multi-beam antennas as specified in the 3GPP specifications.

In this paper, we propose a 28GHz multi-sector antenna to create an efficient indoor coverage area using a small number of antenna elements. A Yagi–Uda antenna element with a dipole configuration employing balun-integrated feeding on a dielectric substrate was used. In addition, by introducing a planar reflector, sidelobe levels and mutual coupling between elements were reduced, thereby achieving an antenna gain of 15 dBi. By alternately arranging 12 antenna elements for vertical and horizontal polarizations in a circular configuration, a 12-sector multi-sector antenna with a diameter of 150 mm was realized. Furthermore, propagation tests conducted in a shielded room simulating an indoor office environment demonstrated that the proposed antenna can be used to construct areas utilizing each branch.

This paper demonstrates that MIMO effects can be achieved with a compact antenna configuration by using the proposed multi-sector antenna for indoor base stations. These results represent a promising technology for the effective utilization of high-frequency bands and are highly commendable as a paper worthy of an IEICE Best Paper Award.