Abstract
This paper proposes a novel compact 4 × 4 butler matrix (BM) with improved bandwidth based on open-circuit coupled-lines and interdigital capacitor unit-cell to develop composite right/left handed (CRLH) transmission-line (TL) metamaterial structure. The BM is implemented by the combination of compact 3dB quadrature hybrid couplers, 0dB crossover and 45° phase shifter on a single FR4 substrate (er = 4.3 and h = 1.66 mm). The simulated and measured result shows that the return loss and isolation loss are better than 14 dB at all the ports, good insertion loss of -7 ± 2dB, which cover the frequency range of 3.2 GHz to 3.75 GHz. The phase difference of -45°, 135°, -135° and +45° are achieved with a maximum average phase tolerance of 5°. The overall dimension of the BM is 70mm × 73.7mm, which shows the compactness of the proposed design that is 75% size reduction and 8.2 times improvement in the bandwidth (550MHz) as compared to conventional BM. The CST microwave studio is used to design and perform the simulations. Additionally, the simulated and measured scattering parameters and phase differences show that they are in good agreement. This compact and improved bandwidth of the proposed BM is suitable for 5G antenna array beamforming network.
Highlights
The evolution in wireless communication systems in terms of enhanced performance by improving data-rate, power dissipation and latency leads to the emergence of 5G [1], [2]
The proposed butler matrix is designed using the composite right/left handed transmission-line metamaterial structure, which is based on open-circuits coupled-lines and interdigital capacitors
The proposed butler matrix has the advantage of compact size (70mm × 73.7mm) and improved bandwidth (550MHz) as compared to the previous designs discussed in the literature and summarized in the previous section
Summary
The evolution in wireless communication systems in terms of enhanced performance by improving data-rate, power dissipation and latency leads to the emergence of 5G [1], [2]. The size of the BM is reduced by 55% as compared to the conventional BM design Another miniaturized BM design is presented in [12] by employing dumbbell-shaped cross-slot patch hybrid couplers and meandered lines based crossover. It achieves the fractional bandwidth improvement of 37.5% and a size reduction of 17%. In this paper, a compact and improved bandwidth BM is proposed by employing four 3dB BLCs based on the open-circuit coupled-lines technique and interdigital capacitor (IDC) CRLH-TL metamaterial structure [21], one 0dB crossover (instead of two 0 dB crossover in the conventional BM) and phase shifters of 45◦.
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