Design of a butler matrix beamforming circuit at 28 GHZ for 5G mobile communication

Abstract

Mobile communication has become prevalent nowadays. The demand for high speed data and information exchange urge on a better communication services. Furthermore, existing services may not able to satisfy the increasing data volume with increasing number of users. The current technology may suffer from congestion and spectrum shortage issue. Thus, 5G is introduced with new spectrum particularly at higher frequencies. However, at high frequencies, a higher propagation loss is expected. The solution is to have a high gain array antenna with particular beamforming features to compensate the high loss. Thus, this work proposes a Butler Matrix beamforming circuit to feed an array at particular 28 GHz for 5G mobile communication. However, the antenna part will not be in the scope of this work. The beamforming circuit will be design, simulate and optimize using CST software. The components namely the coupler, crossover and phase shifter are designed and analyzed separately before integrated to be one Butler Matrix network circuit. Conventional hybrid coupler is designed to operate at desired 28GHz with 90 degrees phase different and equal power divided between the output ports before it is improved with tee junction structure, which reduce the overall dimension without much sacrificing the performances. The coupler then combined to form a crossover with 0 degrees phase different and good isolation. A delay line which give 45 degrees phase shift is designed and connect the structure to form a Butler Matrix beamforming circuit.