Publication: Design implementation of 4 × 4 butler matrix with bandwidth enhancement and size reduction for fifth generation (5g) wireless communication system
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Date
2022-05-01
Authors
Mohd Suhaimi, Nazleen Syahira
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Abstract
Signals are susceptible to reflections from various obstacles resulting in multipath signal propagation delay and degrading the quality of the received signal. As the number of subscribers to wireless communication is increasing at an alarming rate, future wireless communication requires a high data rate, better coverage, improved capacity and higher quality of service. Implementing a Butler matrix is one of the solutions to overcome these issues. However, the conventional 4 × 4 Butler matrix has a bulky size which consists of 10 individual components such as four 3 dB branch-line couplers with 90° output phase differences, two 0° Schiffman phase shifters, two 45° Schiffman phase shifters, two conventional 0 dB crossovers with 90° output phase differences. Besides that, the conventional Butler matrix has high insertion loss due to the additional path from the phase shifters and crossovers. Owing to these issues, an alternative way of implementing the proposed 4 × 4 Butler matrix in a single layer by eliminating four phase shifters and one crossover is proposed in this work. The center frequency is set to 6.5 GHz which lies in the 5G frequency band between 5.9 GHz and 7.1 GHz. The design utilizes two 3 dB cross-slotted patch couplers with 45° output phase difference as a replacement of two conventional 3 dB/90° couplers with two 45° Schiffman phase shifters. This approach contributes to
physical size reduction and better performance. The -3 dB ± 1 dB fractional bandwidth enhancement of coupling coefficient and physical size reduction for the proposed 3 dB/90° cross-slotted patch coupler are 18.77% and 26.32%, whereas 22.52% and 45.72% for the proposed 3 dB/45° cross-slotted patch coupler compared to their conventional designs, respectively. The proposed 4 × 4 Butler matrix exhibits overall fractional bandwidth enhancement of 9.7% and overall physical size reduction of 51.56% compared to the conventional 4 × 4 Butler matrix. The beam scanning of the conventional 4 × 4 switched-beam Butler matrix is covered from -45° to +45°, whereas from -50° to +50° for the proposed 4 × 4 switched-beam Butler matrix. The highest gain of the conventional and proposed 4 × 4 switched-beam Butler matrices are 9.32 dBi and 9.84 dBi, respectively. Therefore, the proposed 4 × 4 switched-beam Butler matrix shows good performances in terms of compactness and beam scanning angles at the output ports.