MIMO Coded Generalized Reduced Dimension Fourier Algorithm for 3-D Microwave Imaging

10.13039/501100000275-Leverhulme Trust under Research Leadership Award (Grant Number: RL-2019-019); 10.13039/501100007914-Brunel University London under Research Development Fund (Grant Number: LBG194); 10.13039/501100007914-2022/2023 Brunel Research Initiative and Enterprise Fund (Grant Number: 12455)

Fourier-Based Near-Field Three-Dimensional Image Reconstruction in a Multistatic Imaging Structure Using Dynamic Metasurface Antennas

Brunel University London Research Development Fund (Grant Number: LBG194); 2022/2023 Brunel Research Initiative and Enterprise Fund (Grant Number: 12455); 10.13039/501100000275-Leverhulme Trust (Grant Number: RL-2019-019)

Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Design of Reconfigurable Intelligent Surfaces for Wireless Communication: A Review

Existing literature reviews predominantly focus on the theoretical aspects of reconfigurable intelligent surfaces (RISs), such as algorithms and models, while neglecting a thorough examination of the associated hardware components. To bridge this gap, this research paper presents a comprehensive overview of the hardware structure of RISs. The paper provides a classification of RIS cell designs and prototype systems, offering insights into the diverse configurations and functionalities. Moreover, the study explores potential future directions for RIS development. Notably, a novel RIS prototype design is introduced, which integrates seamlessly with a communication system for performance evaluation through signal gain and image formation experiments. The results demonstrate the significant potential of RISs in enhancing communication quality within signal blind zones and facilitating effective radio wave imaging

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

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

Smart Surface Radio Environments

This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Metasurface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation, and sensing, some rooted in novel architectures for future mobile communications networks towards 6G

Waveplates based on metasurfaces in the THz range

Los platos de onda basados en metasuperficies son componentes clave en electromagnetismo, ya que permiten un control total de la polarización de las ondas electromagnéticas con la ventaja de presentar estructuras más compactas que los platos de onda convencionales. Además, la aplicación del principio de Pancharatnam Berry (PB) a los platos de media onda (HWP) basados en metasuperficies, permite la manipulación de frentes de onda junto con la conversión de la polarización de las ondas incidentes circularmente polarizadas, simplemente girando los meta-átomos que componen la metasuperficie. Para lograr altos niveles de eficiencia de transmisión con platos de onda basados en metasuperficies, generalmente se requieren diseños multicapa. Esto implica estructuras voluminosas y complica el proceso de fabricación, restando importancia a la ventaja de utilizar metasuperficies. El propósito de esta tesis realizada en la Universidad Pública de Navarra y en L’École Polytechnique Fédérale de Lausanne, Suiza (EPFL) es ofrecer una ventaja tecnológica tanto para el control de polarización como para la manipulación del frente de onda y contribuir al desarrollo de dispositivos basados en metamasuperficies, incluyendo su fabricación y verificación experimental. Los resultados incluyen lo siguiente: Un plato de media onda operando en transmisión, ultradelgado y basado en una metasuperficie en zigzag de dos capas que opera en la parte baja del espectro del THz con un 90% de eficiencia de transmisión, que se demuestra numérica y experimentalmente. Se lleva a cabo un análisis detallado de la robustez del dispositivo con respecto a los desalineamientos de las capas mediante el diseño y la fabricación de dos dispositivos adicionales con el máximo desalineamiento entre capas en ambas direcciones transversales. Una metalente ultradelgada y compacta basada en el principio Pancharatnam Berry con solo dos capas alcanzando un 90% de eficiencia de transmisión, enfocando el frente de onda de una onda incidente polarizada circularmente y convirtiendo su polarización. La estructura es estudiada semi-analítica y numéricamente y medida experimentalmente, comprobándose un excelente comportamiento como HWP PB metalente a 87 GHz. Una aplicación de ingeniería de frentes de onda para la manipulación de los mismos se demuestra numéricamente en el rango de ondas milimétricas mediante la integración de la metalente en un sistema de antena-metalente, que se estudia semi-analíticamente y se corrobora experimentalmente. El sistema convierte la polarización de las ondas polarizadas circularmente, logrando un incremento de la directividad de antena de 17 dB a ⁓35 dB a 87 GHz con un AR inferior a 0.5 dB. Finalmente, se presentan dos configuraciones extra del sistema para trabajar entre los extremos del rango de frecuencia comprendido entre 75 GHz y 105 GHz, con directividades ⁓32 dB y AR < 3 dB.Transmissive waveplates based on metasurfaces are key components in electromagnetism, as they allow for a full control of the electromagnetic wave polarization with the advantage of presenting structures more compact than conventional waveplates. Moreover, applying the Pancharatnam Berry (PB) principle to half-wave plate (HWP) metasurfaces allows the manipulation of wavefronts along with the conversion of the handedness of circularly polarized incident waves by simply rotating the meta-atoms that compose the metasurface. For achieving high levels of transmission efficiency with transmissive waveplates based on metasurfaces, multiple layer designs are usually required. It implies bulky structures and complicates the fabrication process, downplaying the aim of the use of metasurfaces. The purpose of this thesis performed at the Public University of Navarre and at École Polytechnique Fédérale de Lausanne (EPFL) is to offer a technological advantage both for polarization controlling as wavefront manipulation and contribute to the development of metasurface-based devices, including their fabrication and experimental verification. The results include the following: An ultrathin transmissive half-wave plate based on a bi-layered zigzag metasurface operating at the lower-frequency edge of the THz spectrum with a 90% of transmission efficiency, which is numerically and experimentally demonstrated. A detailed analysis of the device robustness with respect to layer misalignments is carried out by designing and fabricating two additional devices with the maximum possible shift between layers along both transverse directions. A compact ultrathin metalens based on the Pancharatnam Berry principle with only two layers with a 90% of transmission efficiency, focusing the wavefront of a circularly polarized incident wave and converting its handedness. The structure is semi-analytically and numerically studied and experimentally measured, verifying an excellent behavior as HWP PB metalens at 87 GHz. A wavefront engineering application for wavefront manipulation is numerically demonstrated in the millimeter-wave range by the integration of the metalens in an antenna-metalens system, which is semi-analytically studied and experimentally corroborated. The system converts the handedness of circular polarized waves, achieving an increment of the antenna directivity from17 dB to ⁓35 dB at 87 GHz with an AR lesser than 0.5 dB. Finally, two extra system configurations are presented to work around the frequency range extremes comprised between 75 GHz and 105 GHz, with directivities ⁓32 dB and AR < 3 dB.Programa de Doctorado en Tecnologías de las Comunicaciones, Bioingeniería y de las Energías Renovables (RD 99/2011)Bioingeniaritzako eta Komunikazioen eta Energia Berriztagarrien Teknologietako Doktoretza Programa (ED 99/2011

On the Road to 6G: Visions, Requirements, Key Technologies and Testbeds

Fifth generation (5G) mobile communication systems have entered the stage of commercial development, providing users with new services and improved user experiences as well as offering a host of novel opportunities to various industries. However, 5G still faces many challenges. To address these challenges, international industrial, academic, and standards organizations have commenced research on sixth generation (6G) wireless communication systems. A series of white papers and survey papers have been published, which aim to define 6G in terms of requirements, application scenarios, key technologies, etc. Although ITU-R has been working on the 6G vision and it is expected to reach a consensus on what 6G will be by mid-2023, the related global discussions are still wide open and the existing literature has identified numerous open issues. This paper first provides a comprehensive portrayal of the 6G vision, technical requirements, and application scenarios, covering the current common understanding of 6G. Then, a critical appraisal of the 6G network architecture and key technologies is presented. Furthermore, existing testbeds and advanced 6G verification platforms are detailed for the first time. In addition, future research directions and open challenges are identified for stimulating the on-going global debate. Finally, lessons learned to date concerning 6G networks are discussed

6G wireless communications networks: a comprehensive survey

The commercial fifth-generation (5G) wireless communications networks have already been deployed with the aim of providing high data rates. However, the rapid growth in the number of smart devices and the emergence of the Internet of Everything (IoE) applications, which require an ultra-reliable and low-latency communication, will result in a substantial burden on the 5G wireless networks. As such, the data rate that could be supplied by 5G networks will unlikely sustain the enormous ongoing data traffic explosion. This has motivated research into continuing to advance the existing wireless networks toward the future generation of cellular systems, known as sixth generation (6G). Therefore, it is essential to provide a prospective vision of the 6G and the key enabling technologies for realizing future networks. To this end, this paper presents a comprehensive review/survey of the future evolution of 6G networks. Specifically, the objective of the paper is to provide a comprehensive review/survey about the key enabling technologies for 6G networks, which include a discussion about the main operation principles of each technology, envisioned potential applications, current state-of-the-art research, and the related technical challenges. Overall, this paper provides useful information for industries and academic researchers and discusses the potentials for opening up new research directions