ABSTRACT
This paper, presents a 4×4 BM based on four direction switch BM antenna array. The proposed design operated at 3.5 GHz. The use of multi-beam antennas or switched-beam antenna arrays (SAAs) promised users of high-gain and large coverage areas for 5G technologies. The BM was implemented by combining 3-dB BLC, two crossovers, and 45o phase shifters fabricated on the RT5880LZ substrate, with using a triangular slot and T-shape based on the BM design. The proposed design focused on the miniaturization and enhancement of the bandwidth. The return loss and isolation were better than -15 dB at all the ports, according to the simulated and measured result showed that with excellent insertion loss -6.1 ± 2 dB. A fractional bandwidth of 49.7% and the overall dimension were reduced to 56% as compared to the conventional BLC and crossover. Hence, the proposed design of BM performed an excellent size reduction of 80% and improvement bandwidth up to 836 MHz compared to the traditional BM. The switched beam directions were measured at -34o, -40o, +32o and +35o at 3.5 GHz for each input port of 1-4 excitation. The proposed design BM is suitable of 5G application.
Keyword:Beamforing, Butler matrix, antenna array, 5G, triangular slot, T-shape, branch line coupler (BLC), microstrip antenna, antenna array.
IntroductionThe demand for wireless technology is substantially increasing because of the rapid growth of wireless technological innovations. Currently, several billion wireless-electronic devices are linked to the internet network, and these figures are expected to rise in the coming years. So, researchers have started to put tremendous effort in the area of 5G technology[1][2][3]. The deployment of 5G wireless, as well as the current and upcoming Beyond 5G (B5G) communication system, point towards a revolutionary change in modern-day telecommunications, leading to a complete paradigm shift in the way end-users will communicate in the coming years [4][5]. Meanwhile, the number of co-channel interference users will increase and improve the inferior quality of service [6][7]. In the development of 5G systems, it is envisaged that switched-beam antenna arrays (SAAs) would play a vital role in obtaining the desired performance at the transceivers. This is the main objective sought by many researchers in the area of beam-forming network. Their focuses have always been on the problem and quality enhancement of the communication link [8]. Hence, the application of switch beam-forming networks (SBFNs) has always been the area of interest among researchers[9]. This technology significantly contributes to wider bandwidth and directional antenna array that can transfer and focus radiated power in the desired direction. It is widely applied in wireless communications [4]. The SBFNs are categorised into several types, such as Nolen matrix [10], Blass matrix [11], Rotman lens [12], and Butler matrix [13]. Butler matrix or BM is a popular technique due to its low cost, simple configuration, and low power dissipation. This technique is widely used in the filed beam-forming of antenna array [14]. BM is a passive device with multiple input and output ports. BM 4×4 consists of four 3-dB directional coupler, two phase shifters, and a crossover [15]. The beam-forming and beam-steering procedures are controlled by the BM design employing an antenna array. The signal-to-noise and clutter ratio is improved by the BM design’s usage of frequency reuse [16]. In the last years, the BM 4×4 has been studied and improved in different ways, such as in [17] and for low loss [18]. The problem with conventional BM large size and narrow-band characteristics [19][20] is that these requirements are unable to meet the fifth generation (5G) application. However, to solve this issue, researchers have started to introduce a new design using many techniques to improve the Butler matrix[21]. The reported literature [22][23][24] has highlighted microstrip artificial transmission lines (ATLs) triangular slot, BM without crossover and phase shifter, and forward wave present in [25]. A reduced BM network has also been implemented at stub loaded TL, as well as presented and the multibeam antenna array has been validate. The size achieved for the Butler matrix was approximately 55% as compared to the traditional BM design [26]. Another way of using miniaturisation butler matrix design is through meandered line and dumbbell-shaped cross-slot technique based on the branch line coupler. The fractional BW was enhanced up to 37.5% and size miniaturised of 17% [27]. The coupler, crossover, and phase shifter sizes were reduced by BLC using artificial transmission lines, as in [28]. Recently, a triangular slot type artificial transmission line (ATL) has also been proposed. The artificial transmission line is, an easy-to-design, compact structure and easy to adjust electrical parameters, which is also helpful to build block for different microwave passive components [29]. The proposed 4 × 4 Butler matrix was design by using software Computer Simulation Technology (CST). This design utilised modified BLC, respectively. The BM Implementation was on the Rogers RT5880LZ with 0.25 mm thickness, relative permittivity εr=2, and loss tangent tan\(\delta\)=0.002. Several BM designs that have been reported in previous work improved the bandwidth and size reduction. However, none of them attained bandwidth improvement and size reduction, together with an excellent performance for 5G beamforming network. Table 1 displays the specification design of the proposed designs. The novelty of this paper includes design of the BLC, crossover and BM by using triangular slot and T-shape structure, and antenna array based zig-zag shape.Table 1. Specification of proposes designs.