Beamforming Networks for 5G. A Literature Review of Butler Matrix

As we are evolving into higher generations of mobile communications for improving our quality of services like low latency, achieving higher data rates, managing exponential increases in number of users and others, we are in need to improve our hardware design of devices (mobile handset and base stations). In this paper, we are going to discuss the changes to be done in the devices to improve the data rates with the help of beamforming techniques that could be implemented through Butler matrix method. Beamforming plays a key role in the fifth generation (5G) and beyond fifth generation (B5G) mobile communication. This paper is organized in a way that, firstly, it discusses the need for beamforming followed by broad divisions of beamforming techniques. Secondly, it focuses on analog beamforming methods like the Blass matrix, Nolen matrix and discusses Butler Matrix in detail. A summary of this work and the expectations for improving the network for future applications are provided in the conclusion. The second part of the paper discusses the different literatures that implement Butler Matrix (BM) as a feed network for Beamforming applications. Various methods to improve the circuit like miniaturizing the circuit, improving the bandwidth of operation, reducing the loss in the circuit, increasing the number of beams produced by the BM, dual band operation, polarization reconfigurability, improving gain and reducing Side Lobe Levels (SLL), etc. are discussed. These improvisations are done by making changes in conventional BM, by eliminating some components, using Metamaterials(MTM) to design components, using multi-layer substrates, designing a special array of antennas, using waveguide technology like Substrate Integrated Waveguide (SIW), using Electronic Band Gap(EBG) method, Defected Ground Surface(DGS) and others methods are discussed.