Circuit Type Multiple Beamforming Networks for Antenna Arrays in 5G and 6G Terrestrial and Non-Terrestrial Networks

Abstract

To support the ever-increasing demand on connectivity and datarates, multiple beam antennas are identified as a critical technology for the fifth generation (5G), the sixth generation (6G) and more generally beyond 5G (B5G) wireless communication links in both terrestrial networks (TNs) and non-terrestrial networks (NTNs). To reduce the cost and power consumption, there is a marked industrial interest in adopting analogue multiple beam antenna array technology. A key sub-system in many of such antenna arrays is the circuit type multiple beamforming network (BFN). This has led to a significantly renewed interest in and new technological developments of Butler matrices, Blass matrices, and Nolen matrices as well as hybrid structures, mostly at millimeter-wave frequencies. To the best of the authors' knowledge, no comprehensive analysis and comparison of circuit type multiple BFNs have been properly reported with focus on 5 G and 6 G applications to date. In this paper, the principle of operation, design, and implementation of different circuit type multiple BFNs are discussed and compared. The suitability of these sub-systems for 5 G and B5G antenna arrays is reviewed. Major technology and research challenges are highlighted. It is expected that this review paper will facilitate further innovation and developments in this important field.INDEX TERMS Fifth generation (5G), sixth generation (6G), beyond 5G (B5G), multiple beam antenna arrays, circuit type beamforming networks (BFNs), Blass matrix, Butler matrix, Nolen matrix, terrestrial network (TN), non-terrestrial network (NTN).This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. GUO ET AL.: CIRCUIT TYPE MULTIPLE BEAMFORMING NETWORKS FOR ANTENNA ARRAYS FIGURE 1. General Layout of a multibeam cellular antenna using 1D circuit type BFNs.

Quasi-Optical Multi-Beam Antenna Technologies for B5G and 6G mmWave and THz Networks: A Review

“…Since Rotman lens was first proposed in 1963 [13], it has been widely used in multibeam antenna systems as a wide band and wide angle beam-forming network [1,4,5,8,12,14]. It is better applied to numerous beam ports and array ports in large-scale scanning array compared with other beam-forming networks.…”

“…Because the wavelengths at mmWave and THz frequencies are physically small, these antenna systems generally have a quasi-optical nature. Therefore, the associated beamforming devices, in contrast to the standard circuit type beamforming networks associated with lower frequency multi-beam antennas [5], need to be designed primarily based on optical theory and principles, as described in [6]. Furthermore, mmWave and THz fields propagate in a pseudo-light fashion and, hence, their interactions with mobile platforms are highly localized.…”

Jammer Mitigation via Beam-Slicing for Low-Resolution mmWave Massive MU-MIMO

“…A Butler matrix is a passive, bidirectional beamforming network consisting of hybrid couplers and fixed phase shifters, and is capable of simultaneously generating multiple beams for antenna arrays [20], [21]. To support multibeamforming, the Butler matrix implements a DFT 2 in a structure analogous to that of the fast Fourier transform (FFT) [22], [23]. This efficient topology as well as the reduced component count (compared to the alternative Blass [24] and Nolen [25] matrices) makes the Butler matrix one of the most prominent circuit-based, analog DFT implementations [23], [26].…”

“…To support multibeamforming, the Butler matrix implements a DFT 2 in a structure analogous to that of the fast Fourier transform (FFT) [22], [23]. This efficient topology as well as the reduced component count (compared to the alternative Blass [24] and Nolen [25] matrices) makes the Butler matrix one of the most prominent circuit-based, analog DFT implementations [23], [26]. Nevertheless, the implementation of large Butler matrices remains impractical.…”

“…While Butler matrices with 180 • hybrid couplers implement a rowpermuted DFT, Butler matrices with 90 • hybrid couplers implement a rotated DFT that lacks a beam at broadside [22]. their implementation is hindered by the more complex routing [23], [26] and the necessity for lower manufacturing tolerances [27]. Another issue in implementing large Butler matrices is an increase in insertion loss [23], [26], [28].…”