Design, Modelling, and Characterisation of Millimetre-Wave Antennas for 5G Wireless Applications

PhDFuture 5G systems and beyond are expected to implement compact and versatile antennas in highly densifi ed millimetre-wave (MMW) wireless networks. This research emphasises on the realisation of 5G antennas provided with wide bandwidth, high gain, adaptable performance, preferably conformal implementation, and feasible bulk fabrication. Ka{band (26.5{40 GHz) is selected based on recent 5G standardisation, and novel antenna geometries are developed in this work on both rigid and flexible substrates by implementing advanced techniques of frequency reconfi guration, multiple-input-multiple- output (MIMO) assembly, as well as wideband and multiband antennas and arrays. Nove lMMW wideband antennas are presented for 5G and spatial diversity at the antenna front-ends is substantially improved by deploying wideband antennas in a MIMO topology for simultaneous multiple-channel communication. However, wideband operation is often associated with efficiency degradation, which demands a more versatile approach that allows the adaptable antenna to select the operating frequency. In this research, high performance recon figurable antennas are designed for frequency selection over Ka- {band. Also, an efficient and conformal antenna front-end solution is developed, which integrates both frequency recon guration and MIMO technology. Gain of the antenna is critically important for 5G systems to mitigate high propagation losses. Antenna design with both high gain and bandwidth is challenging as wideband antennas are traditionally gain-limited, while antenna arrays deliver high gain over a narrow bandwidth. An Enhanced Franklin array model is proposed in this thesis, which aggregates multiband response with high gain performance. Furthermore, novel flexible monopole antenna and array con gurations are realised to attain high gain profi le over the complete Ka{band. These proposed 5G antennas are anticipated as potential contribution in the progress towards the realisation of future wireless networks.EECS Fees Waiver Award and National University of Sciences and Technolog

ELECTRONICAL LY RECONFIGURABLE FS S - INSPIRED TRANSMITARRAY FOR TWO DIMENS IONAL BEAMSTEERING FOR 5G ANDRADAR APPL ICATIONS AT 2 8 GHZ

In this dissertation, the author’s work on a 28 GHz transmitarray capable of antenna beamsteering for various wireless applications, is presented. Such device allows for the adjustment of the radiation pattern of an antenna by changing its main lobe direction, without the need of any mechanical means. A unit-cell based on a square-slot Frequency Selective Surface (FSS) is designed, simulated and optimised through several full-wave simulations, using an electromagnetic solver (CST MWS). Subsequently, the unit-cell was extended to a 10x10 array configuration in order to enable Two-dimensional (2D) beamsteering. This work yielded the fabrication of a prototype composed of four passive transmitarray lens, which were experimentally tested and characterised. Finally, a novel unit-cell based on a double square-slot intended aiming at active beamsteering was also studied and optimised in simulation environment. From this work, it was demonstrated that transmitarray can be seen as feasible alternative to many traditional beamsteering techniques, such as phased antenna arrays, while reducing the RF burden of the overall system using only a single radiation source. This fact, allied with it’s ease of integration, reduced cost and low-profile characteristics make transmitarrays a desirable solution for 5G and RADAR applications, among others

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

Antenna System Design for 5G and Beyond – A Modal Approach

Antennas are one of the key components that empower a new generation of wireless technologies, such as 5G and new radar systems. It has been shown that antenna design strategies based on modal theories represent a powerful systematic approach to design practical antenna systems with high performance. In this thesis, several innovative multi-antenna systems are proposed for wireless applications in different frequency bands: from sub-6 GHz to millimeter-wave (mm-wave) bands. The thesis consists of an overview (Part I) and six scientific papers published in peer-reviewed international journals (Part II). Part I provides the overall framework of the thesis work: It presents the background and motivation for the problems at hand, the fundamental modal theories utilized to address these problems, as well as subject-specific research challenges. Brief conclusions and future outlook are also provided. The included papers of Part II can be divided into two tracks with different 5G and beyond wireless applications, both aiming for higher data rates.In the first track, Papers [I] to [IV] investigate different aspects of antenna system design for smart-phone application. Since Long Term Evolution (LTE) (so-called 3.5G) was deployed in 2009, mobile communication systems have utilized multiple-input multiple-output antenna technology (MIMO) technology to increase the spectral efficiency of the transmission channel and provide higher data rates in existing and new sub-6 GHz bands. However, MIMO requires multi-antennas at both the base stations and the user equipment (mainly smartphones) and it is very challenging to implement sub-6 GHz multi-antennas within the limited space of smartphones. This points to the need for innovative design strategies. The theory of characteristic modes (TCM) is one type of modal theory in the antenna community, which has been shown to be a versatile tool to analyze the inherent resonance properties of an arbitrarily shaped radiating structure. Characteristic modes (CMs) have the useful property of their fields being orthogonal over both the source region and the sphere at infinity. This property makes TCM uniquely suited for electrically compact MIMO antenna design.In the second track, Papers [V]-[VI] investigate new integrated antenna arrays and subarrays for the two wireless applications, which are both implemented in a higher part of the mm-wave frequency range (i.e. E-band). Furthermore, a newly developed high resolution multi-layer “Any-Layer” PCB technology is investigated to realize antenna-in-package solutions for these mmwave antenna system designs. High gain and high efficiency antennas are essential for high-speed wireless point-to-point communication systems. To meet these requirements, Paper [V] proposes directive multilayer substrate integrated waveguide (SIW) cavity-backed slot antenna array and subarray. As a background, the microwave community has already shown the benefits of modal theory in the design and analysis of closed structures like waveguides and cavities. Higher-order cavity modes are used in the antenna array design process to facilitate lower loss, simpler feeding network, and lower sensitivity to fabrication errors, which are favorable for E-band communication systems. However, waveguide/cavity modes are confined to fields within the guided media and can only help to design special types of antennas that contain those structures. As an example of the versatility of TCM, Paper [VI] shows that apart from smartphone antenna designs proposed in Papers [I]-[IV], TCM can alsobe used to find the desirable modes of the linear antenna arrays. Furthermore, apart from E-band communications, the proposed series-fed patch array topology in Paper [VI] is a good candidate for application in 79 GHz MIMO automotive radar due to its low cost, compact size, ability to suppress surface waves, as well as relatively wide impedance and flat-gain bandwidths

Statistical Review Evaluation of 5G Antenna Design Models from a Pragmatic Perspective under Multi-Domain Application Scenarios

Antenna design for the 5G spectrum requires analysis of contextual frequency bands, design of miniaturization techniques, gain improvement models, polarization techniques, standard radiation pattern designs, metamaterial integration, and substrate selection. Most of these models also vary in terms of qualitative & and quantitative parameters, which include forward gain levels, reverse gain, frequency response, substrate types, antenna shape, feeding levels, etc. Due to such a wide variety in performance, it is ambiguous for researchers to identify the optimum models for their application-specific use cases. This ambiguity results in validating these models on multiple simulation tools, which increases design delays and the cost of deployments. To reduce this ambiguity, a survey of recently proposed antenna design models is discussed in this text. This discussion recommended that polarization optimization and gain maximization are the major impact factors that must be considered while designing antennas. It is also recommended that collocated microstrip slot antennas, fully planar dual-polarized broadband antennas, and real-time deployments of combined slot antenna pairs with wide-band decoupling are very advantageous. Based on this discussion, researchers will be able to identify optimal performance-specific models for different applications. This discussion also compares underlying models in terms of their quantitative parameters, which include forward gain levels, bandwidth, complexity of deployment, scalability, and cost metrics. Upon referring to this comparison, researchers will be able to identify the optimum models for their performance-specific use cases. This review also formulates a novel Antenna Design Rank Metric (ADRM) that combines the evaluated parameters, thereby allowing readers to identify antenna design models that are optimized for multiple parameters and can be used for large-scale 5G communication scenarios

Design of new radiating systems and phase shifters for 5G communications at millimeter-wave frequencies

With the arrival of the new generation of communications, known as 5G, the systems that constitute it must offer better performance in terms of data speed, latency and connection density than the previous generation of communications. For 5G, an allocation of the frequency ranges that will support future wireless communications has been established. This allocation is formed by a range of frequencies corresponding to bands below 6 GHz and the other range of frequencies includes bands above 24 GHz. In the latter frequency range, which includes part of the millimeter-wave frequency band (from 30 GHz to 300 GHz), the development of new radio frequency (RF) components is necessary because their design and manufacture is a technological challenge. As the frequency that supports wireless communications increases, propagation losses also increase. Therefore, these losses must be compensated by the radiating systems in 5G to make these communications possible. The RF devices that make up these new systems must provide high antenna gain, be power efficient and offer spatial reconfigurability of the radiated signal. In this thesis, the main objective is the design of both guided and radiating RF devices to provide design solutions for future 5G systems at millimeter-wave frequencies. In particular, the contributions made have been to the design of phase shifters and antenna arrays. To improve efficiency at millimeter-wave frequencies, these devices have been designed in waveguide technology. Phase shifters are essential RF devices to control the phase shift of the electromagnetic wave that will be radiated to a certain spatial direction by an antenna array. The design of beamforming networks requires the implementation of phase shifters that produce a fixed or variable phase shift value. However, the design and fabrication of these devices at millimeter-wave frequencies is a complex task. In this thesis, four designs of waveguide phase shifters that produce both fixed and variable phase shift are presented. For phase shifters that provide a fixed phase shift, the value of this phase shift along the frequency is tuned in a desired manner by using periodic structures with higher symmetries. These types of configurations provide both flexibility in the design process and improved electromagnetic performance such as greater operating bandwidth. All the phase shifters have been implemented in gap-waveguide technology to demonstrate its effectiveness in these devices for millimeter-wave frequencies. Regarding the radiating systems, two feeding strategies have been considered in the design process. First, the design of a 70 GHz centered antenna array implemented in gap-waveguide technology combined with the use of separate waveguides in E-plane is proposed. In this design, the feed is guided through a waveguide corporate-feed network. Second, the design of a reflectarray whose unit cells are formed using three-dimensional geometries is presented. In this case, the feeding is done in free space by radiation from a source antenna. In the previous designs, the fabrication of the prototypes was done by 3D printing based on stereolithography. Finally, using unit cells with three-dimensional geometries, the design of radiating devices with more complex functionalities such as reflection/transmission with high directivity and reconfiguration of the reflected radiation by means of graphene structures are proposed.Con la llegada de la nueva generación de comunicaciones, denominada 5G, los sistemas que la conforman deben ofrecer unas mejores prestaciones en términos de velocidad de datos, latencia y densidad de conexiones respecto a la generación de comunicaciones anterior. Para 5G se ha establecido una asignación de los rangos de frecuencia que van a soportar las futuras comunicaciones inalámbricas. Esta asignación se compone por un rango de frecuencias correspondiente a las bandas por debajo de los 6 GHz y el otro rango de frecuencias engloba a las bandas por encima de los 24 GHz. En este ´ultimo rango de frecuencias, en el cual están incluidas parte de la banda de las frecuencias milimétricas (desde 30 GHz a 300 GHz), es necesario el desarrollo de nuevos componentes de radiofrecuencia (RF) ya que su diseño y fabricación supone un reto tecnológico. Al aumentar la frecuencia que soporta las comunicaciones inalámbricas, las pérdidas por propagación también aumentan. Es por ello por lo que estas pérdidas deben ser compensadas por los sistemas radiantes en 5G para que las comunicaciones sean posibles. Los dispositivos de RF que componen estos nuevos sistemas deben proporcionar una alta ganancia de antena, ser eficientes en términos de potencia y ofrecer reconfigurabilidad espacial de la señal radiada. En esta tesis, el objetivo principal es el diseño de dispositivos de RF tanto guiados como radiantes para ofrecer soluciones de diseño a los futuros sistemas 5G en frecuencias milimétricas. De manera particular, las contribuciones realizadas han sido al diseño de desfasadores y agrupaciones de antenas. Para mejorar la eficiencia en frecuencias milimétricas, estos dispositivos han sido diseñados en tecnología en guía de ondas. Los desfasadores son dispositivos RF esenciales para controlar el desfase de la onda electromagnética que será radiada hacia una cierta dirección espacial por una agrupación de antenas. Las redes de beamforming tienen la necesidad de implementar en su diseño desfasadores que producen un valor de desfase fijo o variable. Sin embargo, el diseño y fabricación de estos dispositivos en frecuencias milimétricas resulta una tarea de alta dificultad. En esta tesis se presenta cuatro diseños de desfasadores en guía de onda que producen un desfase tanto fijo como variable. Para los desfasadores que proporcionan un desfase fijo, el valor de este desfase a lo largo de la frecuencia es ajustado de manera deseada mediante el uso de estructuras periódicas con simetrías superiores. Este tipo de configuraciones proporcionan tanto flexibilidad en el proceso de diseño como una mejora de las características electromagnéticas como puede ser un mayor ancho de banda de operación. Todos los desfasadores realizados han sido implementados en tecnología gap waveguide para demostrar su efectividad en estos dispositivos para frecuencias milimétricas. Respecto a los sistemas radiantes, se han considerado dos estrategias de alimentación en el proceso diseño. En primer lugar, se propone el diseño de un array centrado a 70 GHz implementado en tecnología gap waveguide combinado con el uso de guías de onda separadas en plano E. En este diseño, la alimentación es guiada a través de una red de alimentación corporativa en guía de onda. En segundo lugar, se presenta el diseño de un reflectarray cuyas celdas unitarias son formadas mediante geometrías tridimensionales. En este caso, la alimentación se hace en el espacio libre mediante la radiación de una antena fuente. En los anteriores diseños, la fabricación de los prototipos se realizó mediante impresión 3D basado en estereolitografía. Finalmente, a través del uso de celdas unitarias con geometrías tridimensionales, se proponen el diseño de dispositivos radiantes con funcionalidades más complejas como la reflexión/transmisión con alta directividad y la reconfiguración de la radiación reflejada mediante estructuras con grafeno.Tesis Univ. Granada