Advanced Radio Frequency Antennas for Modern Communication and Medical Systems

The main objective of this book is to present novel radio frequency (RF) antennas for 5G, IOT, and medical applications. The book is divided into four sections that present the main topics of radio frequency antennas. The rapid growth in development of cellular wireless communication systems over the last twenty years has resulted in most of world population owning smartphones, smart watches, I-pads, and other RF communication devices. Efficient compact wideband antennas are crucial in RF communication devices. This book presents information on planar antennas, cavity antennas, Vivaldi antennas, phased arrays, MIMO antennas, beamforming phased array reconfigurable Pabry-Perot cavity antennas, and time modulated linear array

MIMO Evolution Beyond 5G Through Reconfigurable Intelligent Surfaces and Fluid Antenna Systems

With massive deployment, multiple-input-multiple-output (MIMO) systems continue to take mobile communications to new heights, but the ever-increasing demands mean that there is a need to look beyond MIMO and pursue the next disruptive wireless technologies. Reconfigurable intelligent surface (RIS) is widely considered a key candidate technology block to provide the next generational leap. The first part of this article provides an updated overview of the conventional reflection-based RIS technology, which complements the existing literature to include active and semiactive RIS, and the synergies with cell-free massive MIMO (CF mMIMO). Then, we widen the scope to discuss the surface-wave-assisted RIS that represents a different design dimension in utilizing metasurface technologies. This goes beyond being a passive reflector and can use the surface as an intelligent propagation medium for superb radio propagation efficiency. The third part of this article turns the attention to the fluid antenna, a novel antenna technology that enables a diverse form of reconfigurability that can combine with RIS for ultrahigh capacity, power efficiency, and scalability. This article concludes with a discussion of the potential synergies that can be exploited between MIMO, RIS, and fluid antennas

Metamaterials and Metasurfaces

Ye

The design, simulation, and pattern synthesis of novel reflectarrays

The main focus of this thesis is on the development of both a comprehensive understanding and a thorough computational routine of the reflectarray metasurfaces designs, with focuses on a liquid crystal-based reconfigurable reflectarray metasurface and on the phase-retrieval/optimisation techniques for reflectarray-based pattern synthesis. A dielectric-based polarisation converting reflectarray metasurface is also presented, with the advantage of having a thinner profile over the traditional quartz-based half-wave plates. In the introductory sections, a thorough review of the state-of-the-art metasurfaces is presented, with a focus on applications to high-frequency wireless communications, as the motivation of this PhD is on the development of technologies that would facilitate the wireless communication challenges for the 5G-and-beyond frequency spectrum. In this section, a review of array antennas, including phased arrays, reflectarrays, transmitarrays, as well as metasurfaces utilising Mie-resonance, plasmonic resonance, geometric phase (Pancharatnam-Berry phase) and photoconductive material is presented. The following chapter on the theoretical background ensures the understanding of the fundamental mechanisms that will be applied to the study of reflectarray metasurfaces and optimisation routines. The high-frequency propagation associated with beyond-5G wireless communications brings many challenges to the current standards: some of the biggest problems are the much greater path loss and heavy non-line-of-sight signal attenuation. Traditionally, this has been dealt with in phased arrays. However, in the introduction part of this thesis, I show that this becomes impractical due to the requirements of enormous array sizes and expensive high-frequency phase shifters. Therefore, in our research, we have focused on reconfigurable reflectarrays as an intermediate solution to alleviate the tough propagation challenges faced by beyond-5G wireless communications. The reconfigurable reflectarray can either be designed to reflect off from a nearby mobile cell site to enhance the signal strength for non-line-of-sight areas, or it can include an integrated source to function independently, reducing the losses associated with power amplifiers and complex circuitries associated with the enormous array sizes. This thesis aims to produce a high-frequency tailored reconfigurable reflectarray design, which combines the conceptual advantages from state of-the-art lumped-element-based and liquid crystal-based reflectarrays. As shown in the literature review section, most recent researches on lumpedelement- based reconfigurable reflectarrays are designed for the sub 40 GHz frequencies; with higher frequencies, the intrinsic losses associated with lumped-elements such as PIN diodes make them unsuitable choices. On the other hand, liquid crystals have been used as a tunable material for different radio-frequency applications; however, most state-of-the-art designs of liquid crystal-based reflectarrays do not incorporate individual biasing control for maximum beam-control. There are also challenges faced with individually-biased reconfigurable reflectarrays. Traditionally, phased arrays can perform single beam-scanning or multiple beam-scanning with the control of multiple sub-arrays. We intend to achieve more complex beam-functionalities (such as vortex, null, and magnitude-specific beams) within the domain of manipulating one individual array. This is already possible with optimisation algorithms such as the genetic algorithm. However, traditional optimisers such as the genetic algorithm and particle swarm optimisation are far too slow to be implemented in an “online” mode, where the algorithm runs onboard the reflectarray to give low-latency solutions. The “online” optimisation mode would be very beneficial as it would reduce the channel occupation from the transmission of configuration information and thus increase channel capacity. In this thesis, I aim to develop an individually biased liquid crystal-based reconfigurable reflectarray for >100 GHz frequencies. I also aim to develop an algorithm that is sufficiently quick to have the potential to be practically utilised as an onboard pattern synthesis optimisation method. Additionally, using the same design principles, I have designed an all-dielectric-based reflectarray metasurface that acts as a polarisation-converting quarter-wave plate, which is much thinner than traditional quartz-based quarter-wave plates. In the Research Results and Publications chapter, a complete procedure for the design of LC-based reconfigurable and dielectric-based nonreconfigurable reflectarray metasurfaces is presented, where much of the content comes from the author’s own publications[52, 78, 50, 51]. This thesis provides details on the computational tools/programs used, cross-platform routines development with CST Studio Suite, MATLAB and VBA, and the pattern synthesis algorithm, whereby a genetic algorithm is employed for the global optimisation, and an improved Gerchberg-Saxton algorithm is developed and adapted to the application of faster local optimisation for the pattern synthesis. For the all-dielectric reflectarray metasurface, the further functionality of polarisation conversion (linear to circular and circular to linear) is demonstrated on top of the beam-manipulation capabilities of the reflectarrays. The reflectarray metasurfaces can be designed to beamform, beamsteer, beamsplit/multibeam, as well as achieve novel beam profiles such as the vortex profile. Originally, the idea was to completely focus on the liquid crystal-based study and to develop a down-scaled 28 GHz proof-of-concept, for which partial work had already begun (the simulation, optimisation and initial planning on the construction with collaborators from other departments); however, due to the pandemic and numerous other uncontrollable factors, this was later discarded and replaced by remaining on and extending upon the computational studies, to further understand and improve the pattern synthesis algorithms and the other types of phase-change metasurfaces

Development and characterization of metallo-dielectric hybrid nanomaterials

The rational combination of dielectric and metallic nano particles brings novel optical properties to conventional subwavelength structures. This thesis introduces the optoplasmonic geometries demonstrating versatile ability in both far and near field modification within nano scale. Template-assisted self-assembly approaches are applied creating nano entities with titanium dioxide and gold nano spheres. A top-bottom mono hybrid unit and interdigitated array are developed. With the examination of the elastic and inelastic response of these hybrid materials, physical models are simulated to depict the scenario of varied geometry and combination of nano particles. In contrast to solely metal or dielectric particle arrays, this type of artificial material not only enhances the near electric field intensity within the metal nano cluster hot spots, but also expands the overall volume of enhanced electric field. Further study reveals that the additional enhancement and redistribution of near field are derived from the coupling between the nano gold cluster plasmon resonance and the in-plane diffractive mode of the dielectric array. The redirected emission profile of the fluorescent dyes within the hybrid array is explored

Holographic MIMO Communications: Theoretical Foundations, Enabling Technologies, and Future Directions

Future wireless systems are envisioned to create an endogenously holography-capable, intelligent, and programmable radio propagation environment, that will offer unprecedented capabilities for high spectral and energy efficiency, low latency, and massive connectivity. A potential and promising technology for supporting the expected extreme requirements of the sixth-generation (6G) communication systems is the concept of the holographic multiple-input multiple-output (HMIMO), which will actualize holographic radios with reasonable power consumption and fabrication cost. The HMIMO is facilitated by ultra-thin, extremely large, and nearly continuous surfaces that incorporate reconfigurable and sub-wavelength-spaced antennas and/or metamaterials. Such surfaces comprising dense electromagnetic (EM) excited elements are capable of recording and manipulating impinging fields with utmost flexibility and precision, as well as with reduced cost and power consumption, thereby shaping arbitrary-intended EM waves with high energy efficiency. The powerful EM processing capability of HMIMO opens up the possibility of wireless communications of holographic imaging level, paving the way for signal processing techniques realized in the EM-domain, possibly in conjunction with their digital-domain counterparts. However, in spite of the significant potential, the studies on HMIMO communications are still at an initial stage, its fundamental limits remain to be unveiled, and a certain number of critical technical challenges need to be addressed. In this survey, we present a comprehensive overview of the latest advances in the HMIMO communications paradigm, with a special focus on their physical aspects, their theoretical foundations, as well as the enabling technologies for HMIMO systems. We also compare the HMIMO with existing multi-antenna technologies, especially the massive MIMO, present various...Comment: double column, 58 page

Solid-state microwave heating for biomedical applications

The research conducted in this thesis aims to develop an efficient microwave delivery system employing miniature resonant microwave cavities, targeted at compact, flexible and ideally field-deployable microwave-assisted diagnostic healthcare applications. The system comprises a power amplifier as a solid-state microwave source and a load - as a single mode cavity resonator to hold the sample. The compactness of the practical microwave delivery system relies on the direct integration of the sample-holding cavity resonator to the power amplifier and inclusion of the built-in directional coupler for power measurements. The solid state power transistors used in this research (10W-LDMOS, 10W-GaN) were provided by the sponsoring company NXP Inc. In practical microwave delivery applications, the impedance environment of the cavity resonators change significantly, and this thesis shows how this can be systematically utilized to present the optimal loading conditions to the transistor by simply designing the series delay lines. This load transfer technique, which critically can be achieved without employing bulky, lossy and physically larger output matching networks, allows high performance of the power amplifier to be achieved through waveform engineering at the intrinsic plane of the transistor. Starting with the impedance observation of a rectangular cavity, using only series delay lines allowed the practical demonstration of the high power and high efficiency fully integrated inverse class-F (F-1) power amplifier. Temperature is an important factor in a microwave heating and delivery system as it changes the impedance environment of the cavity resonator. This natural change in both cavity and sample temperature can be accommodated through simplified series matching lines and the microwave heating system capable of working over substantial bandwidth was again practically demonstrated. The inclusion of the coupler maintained the compactness of the system. In the practical situations envisaged, the microwave delivery system needs to accommodate natural variation between sample volumes and consistencies for heating. The experimental work considered the heating of different sample volumes ii of water, and characterizing the change in the natural impedance environment of the cavity as a result. It was shown how the natural impedance variation can not only be accommodated, but also exploited, allowing ‘continuous’, high-efficiency performance to be achieved while processing a wide range of sample volumes. Specifically, using only transistor package parasitic, the impedance of the cavity itself together with a single series microstrip transmission line allows a continuous class-F-1 mode loading condition to be identified. Through different experiments, the microwave delivery systems with high-performance are demonstrated which are compact, flexible and efficient over operational bandwidth of the cavity resonators

Miniaturized Microwave Devices and Antennas for Wearable, Implantable and Wireless Applications

This thesis presents a number of microwave devices and antennas that maintain high operational efficiency and are compact in size at the same time. One goal of this thesis is to address several miniaturization challenges of antennas and microwave components by using the theoretical principles of metamaterials, Metasurface coupling resonators and stacked radiators, in combination with the elementary antenna and transmission line theory. While innovating novel solutions, standards and specifications of next generation wireless and bio-medical applications were considered to ensure advancement in the respective scientific fields. Compact reconfigurable phase-shifter and a microwave cross-over based on negative-refractive-index transmission-line (NRI-TL) materialist unit cells is presented. A Metasurface based wearable sensor architecture is proposed, containing an electromagnetic band-gap (EBG) structure backed monopole antenna for off-body communication and a fork shaped antenna for efficient radiation towards the human body. A fully parametrized solution for an implantable antenna is proposed using metallic coated stacked substrate layers. Challenges and possible solutions for off-body, on-body, through-body and across-body communication have been investigated with an aid of computationally extensive simulations and experimental verification. Next, miniaturization and implementation of a UWB antenna along with an analytical model to predict the resonance is presented. Lastly, several miniaturized rectifiers designed specifically for efficient wireless power transfer are proposed, experimentally verified, and discussed. The study answered several research questions of applied electromagnetic in the field of bio-medicine and wireless communication.Comment: A thesis submitted for the degree of Ph

Réalisation d'antennes hybrides de type BIE à base de résonateurs diélectriques à 60 GHz

Un système de communication fiable dans un environnement confiné, en particulier les mines souterraines, peut largement accroître la sécurité et la production. Actuellement, les réseaux de communication sans fil en milieu confiné offrent un débit maximal de 1 Gbits/s. Toutefois, la disponibilité de systèmes offrants des débits de l'ordre de 2 à 10 Gbits/s deviendra dans un proche avenir, une nécessité compte-tenu de l'introduction des systèmes 4G avancés et les technologies 5G qui pointent à l’horizon. L’utilisation de fréquences élevées, particulièrement en bandes millimétriques, telle que la bande ISM à 60 GHz offrant 7 GHz de bande passante, est l'une des voies les plus directes et les plus simples pour atteindre un débit souhaitable entre 2-10 Gbits/s. Il est bien connu toutefois que les signaux à 60 GHz se propagent de façon erratique dans les endroits où se trouvent de nombreux obstacles, les composantes réfléchies et diffractées étant considérablement atténuées. Le type de polarisation de l'antenne d'émission et de réception est l'un des critères affectant la qualité de réception du signal, en plus des pertes additionnelles liées à l'absorption par l'oxygène dans l’air et les pertes de propagation associées au parcours. Pour palier partiellement à ces problèmes, les antennes doivent être directionnelles à polarisation circulaire avec un gain élevé et une large bande passante. Ce travail présente une nouvelle approche pour améliorer les propriétés de rayonnement des antennes BIE (Bande Interdite Électromagnétique) en utilisant une combinaison entre les antennes à résonateurs diélectriques DRA (Dielectric Resonator Antenna) et les superstrats métamatériaux pour profiter des avantages individuels de chacun d’eux. L’objectif est de concevoir, étudier analytiquement, numériquement et expérimentalement de nouvelles structures performantes de type BIE et de caractériser leur potentiel en termes de la bande passante, du gain, de l’efficacité et de la polarisation pour un fonctionnement optimal autour de 60 GHz, conformément aux exigences d’un canal minier. Initialement, une antenne émettrice originale BIE fonctionnant à 60 GHz, caractérisée par un gain élevé et une polarisation circulaire à large bande est proposée. Cette antenne est constituée d’un résonateur diélectrique en forme de croix (XDRA) et elle est utilisée comme une source d’alimentation pour générer la polarisation circulaire avec une couche supérieure de type FSS (surface sélective en fréquence) pour améliorer le gain et la bande passante de la source d’excitation. Ensuite, une nouvelle approche analytique pour calculer les propriétés de rayonnement des antennes BIE est développée. Pour satisfaire aux exigences des ondes millimétriques en termes de gain, on présente une autre antenne hybride basée sur la combinaison de la théorie des réseaux et la notion des antennes BIE monosource. Cette nouvelle structure multisources permet d’atteindre une amélioration de gain de 3.5 dB par rapport à l’antenne monosource mais, la bande passante de ces structures reste encore incompatible avec de nombreuses applications à 60 GHz. Pour remédier au problème de la bande passante limitée, une nouvelle approche hybride est subséquemment introduite. Cette technique est basée sur l’excitation de la structure BIE par des antennes à résonateur diélectrique multi segments et, ensuite, le concept du superstrat métamatériau est introduit pour améliorer le produit gain- bande passante. Finalement, pour rendre la communication plus flexible soit que les antennes peuvent être utilisées simultanément en tant qu’émetteur et récepteur, une structure BIE unique à polarisation configurable est conçue. La structure est composée d'une excitation sous la forme d'une antenne à résonateur diélectrique pyramidal DRA recouvert avec un superstrat FSS. Ce dispositif est capable de basculer entre la polarisation circulaire et linéaire par une simple rotation mécanique du résonateur diélectrique de 45 degrés. L'avantage de cette structure réside dans le fait que les propriétés de la bande passante, du gain, de l’efficacité et de la forme des diagrammes de rayonnement sont maintenues stables lors de la commutation entre les deux configurations de polarisation circulaire et linéaire.A reliable communication system in confined areas, in particular underground mines, can largely increase safety and production output. Today’s, wireless data rates in confined environments are limited to a maximum of about 1 Gbits/s. The demand for wireless 2 to 10 Gbits/s data rate systems will , however, become a necessity due to the introduction of advanced 4G technologies and the foreseeable implementation of 5G. The potential use of millimeter wave communication systems, such as ISM 60 GHz band, which offers 7 GHz of bandwidth, is one of the most direct and easiest ways to achieve such high data rate of 2–10 Gbits/s. It is well known that 60 GHz signals propagate erratically through in environments with many obstructions, since both the reflected and diffracted waves are significantly attenuated. The polarization of the transmitting and receiving antennas is one of the important parameter to take into account, along with additional losses due to oxygen absorption and propagation path loss in assessing received signal quality. These situations limit the communication achievable distance link and overcoming of these disadvantages requires circular polarization directive antennas with a high gain and broadband capability. This work presents a novel approach to improve the radiation properties of Electromagnetic Band Gap antennas (EBG) using a combination between dielectric resonator and metamaterial superstrate to take advantage of the individual benefits of each of them. The aim is to design, study analytically, numerically and experimentally new performant EBG structures and characterize their potential in terms of bandwidth, gain, efficiency and polarization for an optimum performance around 60 GHz fulfilling the requirements of a mining environment. Initially, an original transmitting 60 GHz antenna with high gain, broadband, circularly polarized Electromagnetic Band Gap (EBG) antenna is presented. The designed antenna is configured with a superstrate based on a frequency selective surface (FSS) placed in front of a Cross Dielectric Resonator (XDRA), installed into a ground plane, which acts as an excitation source. Then, a new analytical approach is developed to derive the radiation properties of the proposed EBG antenna. To satisfy millimeter wave requirements in terms of gain, another hybrid antenna based on the combination of superstrate structures and array technology has been developed. This new multi-source structure has achieved a gain improvement of 3.5 compared to the monosource antenna. However, the bandwidth of these structures remains incompatible with many applications at 60 GHz. To overcome the problem of the limited bandwidth, a new hybrid approach is introduced. This technique is based, on the excitation of the structure by a multilayer cylindrical dielectric resonator antenna, and then, the concept of metamaterial superstrate is introduced for enhancing the gain-bandwidth product. Finally, to make communication more flexible so that the antennas can be used for transmission and reception simultaneously, a new reconfigurable polarisation EBG antenna is designed. The structure is composed of an exciting pyramidal DRA source covered with FSS superstrate. The device can switch between circular and linear polarization by a simple mechanical rotation of the pyramidal DRA by 45°. The advantage of this structure resides in the fact that it maintain stable bandwidth gain, efficiency and radiation properties when switching between the two configurations of circular and linear polarization