Due to the rapid development of wireless communication technologies, the number of wireless users are radically increasing. Currently, $\sim 23$ billion wireless devices are connected to the internet, and these numbers are expected to increase manifolds in the years to come. The technology growth of the fifth-generation (5G) wireless systems will be needed to meet this high demand of the network. 5G wireless systems offer data-rates of up to 10Gbps, 1-ms latency, and reduced power consumption. It is a known fact that 5G wireless systems will be exploiting beyond the presently used 3 GHz microwave and millimetre-wave (mm-wave) frequency bands. This is the primary driver in the development of the 5G wireless system. Multi-beam Phased array antenna (PAA) systems are typically used in the deployment of 5G systems for high-gain and directionality. In current 5G and future Beyond 5G (B5G) antenna array systems, beamforming networks (BFNs) such as the Butler Matrix (BM) will play a key role in achieving multi-beam characteristics. So, this paper presents an extensive review of the BM based BFNs, and discusses which type of BM will be suitable for the phased array antenna (PAA) systems in the upcoming 5G and next-generation of B5G wireless systems. Moreover, this paper also summarizes the different types of BM designs based on the number of layers. The BMs are classified into the bi-layer, tri-layer, and four-layer structures. It includes different techniques that have been used to solve the problem of crossing, narrow bandwidth, and size reduction of the BM. From the previous studies, it is found that most of the past research work was performed using the bi-layer BM system, whereas the difficult geometries like tri- and four-layer BM are avoided due to their complex fabrication process. It is also found in this paper that the metamaterial (MTM) based bi-layer BM achieves low insertion-loss and phase-error, excellent bandwidth and compact size, and good S-parameter performance, which makes them an ideal BFN candidate for the upcoming 5G and next-generation B5G systems.

/pdf/butler-matrix-based-beamforming-networks-for-phased-array-cdd5d4ds7p.pdf

Butler Matrix Based Beamforming Networks for Phased Array Antenna Systems: A Comprehensive Review and Future Directions for 5G Applications

Next-generation communication systems and wearable technologies aim to achieve high data rates, low energy consumption, and massive connections because of the extensive increase in the number of Internet-of-Things (IoT) and wearable devices. These devices will be employed for many services such as cellular, environment monitoring, telemedicine, biomedical, and smart traffic, etc. Therefore, it is challenging for the current communication devices to accommodate such a high number of services. This article summarizes the motivation and potential of the 6G communication system and discusses its key features. Afterward, the current state-of-the-art of 5G antenna technology, which includes existing 5G antennas and arrays and 5G wearable antennas, are summarized. The article also described the useful methods and techniques of exiting antenna design works that could mitigate the challenges and concerns of the emerging 5G and 6G applications. The key features and requirements of the wearable antennas for next-generation technology are also presented at the end of the paper. 

/pdf/a-road-towards-6g-communication-a-review-of-5g-antennas-f5u7fo3x.pdf

A Road towards 6G Communication—A Review of 5G Antennas, Arrays, and Wearable Devices

This study focuses on the design, simulation, and fabrication of a coplanar waveguide miniaturised wearable antenna that is fully implemented in textile materials and operable at 2.45/5.8 GHz for wireless local area network applications. This antenna is assumed to be placed near the human body, so that it needs to be miniaturised with excellent performances. To increase the performance of the short-distance textile antenna and to control the specific absorption rate, an artificial magnetic conductor (AMC) is preferred as a reflector plane. The volume of the proposed antenna with AMC is 75 × 50 × 6 mm
 3
, the simulation and measurement results are in good agreement and show that the antenna performances perform better results in comparison with the one reported so far in the literature while having a smaller volume. AMC significantly improves the performance of the antenna. The gains of the antenna are 8.2 and 9.95 dBi at 2.45 and 5.8 GHz, respectively (an increase of 3 dB compared with an antenna without AMC).

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2017.0476

Performance of dual-band AMC antenna for wireless local area network applications

Next-generation communication systems and wearable technologies aim to achieve high data rates, low energy consumption, and massive connections because of the extensive increase in the number of Internet-of-Things (IoT) and wearable devices. These devices will be employed for many services such as cellular, environment monitoring, telemedicine, biomedical, and smart traffic, etc. Therefore, it is challenging for the current communication devices to accommodate such a high number of services. This article summarizes the motivation and potential of the 6G communication system and discusses its key features. Afterward, the current state-of-the-art of 5G antenna technology, which includes existing 5G antennas and arrays and 5G wearable antennas, are summarized. The article also described the useful methods and techniques of exiting antenna design works that could mitigate the challenges and concerns of the emerging 5G and 6G applications. The key features and requirements of the wearable antennas for next-generation technology are also presented at the end of the paper.

A millimeter-wave (mmWave) textile antenna operating at 26 GHz band for 5G cellular networks is proposed in this paper. The electromagnetic characterization of the textile fabric used as substrate at the operating frequency was measured. The textile antenna was integrated with an electromagnetic bandgap (EBG) structure and placed on a polyester fabric substrate around the antenna. Results showed that the proposed EBG significantly improved the performance of the antenna. The gain and energy efficiency at 26 GHz were 8.65 dBi and 61%, respectively (an increase of 2.52 dB and 7% compared to a conventional antenna), and the specific absorption rate (SAR) was reduced by more than 69.9%. Good impedance matching of the fabricated antenna at the desired frequency was observed when it was bent and worn on the human body. The structure is simple, compact, and easy to manufacture. It may well be suitable for integration into applied clothing in various fields, especially for future IoT applications.

https://www.mdpi.com/2079-9292/10/2/154/pdf

A Textile EBG-Based Antenna for Future 5G-IoT Millimeter-Wave Applications

A coplanar tri-band wearable antenna combined with an electromagnetic bandgap (EBG) structure is described for sub-6GHz 5G and wireless local area network (WLAN) applications. The proposed antenna is fully implemented in textile materials thus offering a robust, compact, and discreet solution to meet the requirements of wearable applications. The addition of the EBG structure increases the textile antenna performance in terms of radiation patterns in the presence of the human body. The experimental results show that the proposed design exhibits tolerance to various bending conditions as well as loading by body tissues. In addition, to ensure the safety of the design for human health, the values of the specific absorption rate (SAR) have been reduced by more than 95%, which complies with the international standard. This design could thus be considered as a good candidate for IoT applications compared to the current state of the art while having a tri-band behavior and smaller volume.

/pdf/design-of-low-profile-and-safe-low-sar-tri-band-textile-ebg-2y1j2j70gj.pdf

Design of Low-Profile and Safe Low SAR Tri-Band Textile EBG-Based Antenna for IoT Applications

This paper presents results of direction of arrival (DOA) estimation using multiple signal classification (MUSIC), Root-MUSIC, and estimation of signal parameters via rotational invariance technique algorithms. As is well known, these algorithms are mainly based on the specific properties of the signal covariance matrix as well as the decomposition of the observation space into two subspaces, one for the signal and the other for the noise. Here, we are particularly interested in the quality of sources localization considering only the case of uncorrelated radio frequency signals impinging on an antenna array. A measurement system consisting of a linear array antenna and a five-port network applicable to a demodulator such as a receiver is used for the DOA estimation process. Co-simulations performed with the Advanced Device System and Matlab yielded interesting results not only on their performance but also on their limitation.

The application of high-resolution methods for DOA estimation using a linear antenna array

This paper focuses on the design of a planar 4×4 butler matrix functioning at 2.45 GHz band frequency. The purpose is to exploit this matrix as a beam forming network generating orthogonal beams oriented towards various directions. For that, we have implemented a simple microstrip structure with single layer. We have also integrated some microwave devices, namely phase-shifters, 3 dB couplers and cross-couplers.

Design of a 4×4 butler matrix for beamforming antenna applications

This paper describes the antenna performances made from common clothing fabrics for 5G and Internet of Things (IoT) applications by employing electromagnetic bandgap (EBG) structures as the substrate of the antenna for gain enhancement in millimeter-wave frequency. A suspended transmission line method has been taken into account for the characterization of the EBG structure to obtain the optimum design. Furthermore, the optimum unit cell, which is loaded onto the antenna, is easy to implement and allows obtaining a Peak Gain of 9.79 dBi in 26 GHz band.

Imen Sfar

Papers

A Textile EBG-Based Antenna for Future 5G-IoT Millimeter-Wave Applications

Design of Low-Profile and Safe Low SAR Tri-Band Textile EBG-Based Antenna for IoT Applications

The application of high-resolution methods for DOA estimation using a linear antenna array

Design of a 4×4 butler matrix for beamforming antenna applications

A millimeter-wave textile antenna loaded with EBG structures for 5G and IoT applications