Multi-Functional Antenna Structures for 4G/5G Wireless Communication Devices

The performance of a wireless communication system is significantly influenced by a wide rangeof factors, including weather, multi-path effects, polarization mismatch of sending and receivingantennas, and limited bandwidth. The future trends of wireless communication systems need high datarates, better quality, coverage enhancement, capacity improvement, and adaptive features to increasesystem performance and to overcome the ever-increasing data rates requirements. In addition, wirelesscommunication systems are mixtures of many frequency bands and standards. Therefore, the need formultiple features from a single radiator in a very compact size is a significant research problem in themodern era. To that end, this study aims to improve the existing and upcoming wireless communicationsystems employing multi-functional antenna structures that can change their properties to cope withfrequency, polarization, and radiation patterns challenges. Moreover, multiple-input and multiple-out(MIMO) configuration will also be utilized to further improve the system capacity and allow multiplepath propagation.In this project, multi-bands, multi-modes, multi-functional antennas are investigated. For theupcoming 5G mm-wave technology, antennas that can provide multi and high-gain beams are desirable.However, in the transition to the 5G technology, sub-6 GHz (4G/WLAN) technology is still used.The reconfigurable structure can significantly improve the capacity and link quality of the sub-6GHz system. Thus, this project first aims to design a multi-functional (reconfigurable) antennaarray (Design 1) at sub-6 GHz whose polarization and operating frequency can be reconfigured in asignificant range. The target operating band is around 3.6 GHz, which can be used for 4G and 5Glower band applications. The electronic reconfiguration mechanism using varactor diodes is utilizedwith a patch antenna to produce frequency tuning and 90 degree phase difference for the polarization tuning.The second part examines various realizations of integrated antenna designs (Design 2-Design 5)and their optimizations according to the specific application. In this part, the core contributions are theusage of the rectangular slot, tapered slot, and dipole geometries as multi-functional antenna structures.The aim is to combine both microwave and mm-wave communication standards using a single compactantenna structure. The Design 2 consists of a rectangular slot antenna which operates at 2.6 and28 GHz. The design has the capability to reconfigure its operating frequency as similar as Design 1at microwave band and provides a wide frequency band at mm-wave. A novel frequency switchingmechanism, which is based on a connected antenna array concept, is proposed to combine microwave(sub-6 GHz) and mm-wave frequency bands. In particular, a simple rectangular slot is utilized, whichcan operate both as a slot antenna at 2.6 GHz and a connected slot antenna array at 28 GHz.At low frequency, MIMO configuration is mostly used to enhance the system performance, i.e.increasing data density and improving the link budget. One of the most critical requirements in MIMOapplication is the high isolation among radiating elements. In the Design 3, a tapered slot (Vivaldiantenna) is proposed which has dual-function. It is used to improve the isolation between 2 elementmonopole MIMO antenna system at sub-6 GHz band and resonates as an end-fire high gain antenna atmm-wave band. Two different configurations (rectangular and circular) using single and an array oftapered slots are implemented for wireless access point and mobile phone applications, respectively.The targeted bands are 2.4 GHz, 2.6 GHz, 3.5 GHz, 5:2 GHz, and 28 GHz.For the goal of a complete integrated antenna system that can operate at very low microwave bandat 850 MHz and very wideband 1.9-2.6 GHz for 4G, at 2.45 for WiFi and 28 GHz for 5G bands, asimple MIMO antenna system (Design 4) is proposed based on an open-ended slot antenna and taperedslot arrays. The open-ended slot antenna is designed in a way that it resonates at multiple sub-6 GHzbands and leaves a free space to install mm-wave tapered slot arrays. Such configuration provides avery compact and hybrid antenna system, thus suitable for modern mobile devices operating at 4G/5Gbands.For the ultimate aim of achieving a common-aperture and compact antenna structure with largerspace coverage at mm-wave band, the realization of an integrated antenna system (Design 5) isproposed. As a combination of a dipole and tapered slots, the proposed design operates at multi-bands,i.e. sub-6 GHz at 3.6 GHz and mm-wave at 28 GHz. The antenna system starts by designing the dipoleto operate at 3.6 GHz. It is fed by a modified balun consisting of a tapered slot and a microstrip line.Here, the tapered slot has a dual feature, i.e. it is used to excite the dipole at 3.6 GHz and works asa tapered slot antenna at 28 GHz. Only a single feeder is intelligently optimized and used for bothstructures making the design unique and provides an extremely large frequency ratio. Moreover, thedipole’s arms are utilized as an antenna footprint for two tapered slot mm-wave arrays, making thedipole dual-functional. The tapered slot antenna and the mm-wave arrays are optimized in a way thatthe main beams point at different directions. By this configuration, the design is able to cover an angleof 120o of space in theta direction.In summary, the proposed work provides a framework to design integrated antenna systems for4G/5G wireless communication devices. Moreover, the proposed antenna designs have contributedsignificantly to the antenna community for an effective means of the utilization of rectangular slot,tapered slot, and dipole antennas as multi-functional antenna structures to design compact and hybrid4G/5G antennas.