Doctor of Philosophy

dissertationMicrowave/millimeter-wave imaging systems have become ubiquitous and have found applications in areas like astronomy, bio-medical diagnostics, remote sensing, and security surveillance. These areas have so far relied on conventional imaging devices (empl

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

International Workshop on Finite Elements for Microwave Engineering

When Courant prepared the text of his 1942 address to the American Mathematical Society for publication, he added a two-page Appendix to illustrate how the variational methods first described by Lord Rayleigh could be put to wider use in potential theory. Choosing piecewise-linear approximants on a set of triangles which he called elements, he dashed off a couple of two-dimensional examples and the finite element method was born. … Finite element activity in electrical engineering began in earnest about 1968-1969. A paper on waveguide analysis was published in Alta Frequenza in early 1969, giving the details of a finite element formulation of the classical hollow waveguide problem. It was followed by a rapid succession of papers on magnetic fields in saturable materials, dielectric loaded waveguides, and other well-known boundary value problems of electromagnetics. … In the decade of the eighties, finite element methods spread quickly. In several technical areas, they assumed a dominant role in field problems. P.P. Silvester, San Miniato (PI), Italy, 1992 Early in the nineties the International Workshop on Finite Elements for Microwave Engineering started. This volume contains the history of the Workshop and the Proceedings of the 13th edition, Florence (Italy), 2016 . The 14th Workshop will be in Cartagena (Colombia), 2018

Metamaterials and Metasurfaces

Ye

DoA and ToA Estimation, Device Positioning and Network Synchronization in 5G New Radio : Algorithms and Performance Analysis

Location information plays a significant role not only in our everyday life through various location-based services, but also in emerging technologies such as virtual reality, robotics, and autonomous driving. In contrast to the existing and earlier cellular generations, positioning has been considered as a key element in future cellular networks from the very beginning of the fifth generation (5G) standardization process. Even though the earlier generations are capably of providing coarse location estimates, the achieved accuracy is far from the expected even sub-meter positioning accuracy envisioned in the context of 5G networks. In general, 5G new radio (NR) networks provide a convenient infrastructure for positioning by means of wider bandwidths, larger antenna arrays, and even more densely deployed networks especially at high millimeter wave (mmWave) frequencies. Building on dense 5G NR networks, this thesis focuses on the development of novel network-centric positioning frameworks by exploiting the existing NR reference signals. The contributions in this thesis can be grouped into topics based on the considered frequency ranges and the employed beamforming (BF) schemes therein. First, novel cascaded algorithms for sequential device positioning are proposed assuming 5G NR networks operating at the lower sub-6 GHz frequency range and equipped with digital BF capabilities. In the first stage of the cascaded solution, two sequential estimators are proposed for joint direction of arrival (DoA) and time of arrival (ToA) estimation facilitating the received reference signals. Thereafter, the second-stage sequential estimators employing the obtained DoA and ToA estimates are proposed for joint positioning and network synchronization resulting in not only device location estimates, but also clock parameter estimates that are obtained as a valuable by-product. Such a choice stems from the fact that the ToA estimates are not feasible for positioning as such due to the clock instabilities in low-cost devices and the insufficient level of synchronization in the cellular networks. Second, a similar cascaded algorithm for joint positioning and network synchronization is proposed in the context of dense mmWave 5G networks and fundamentally different analog BFs. In particular, a novel joint DoA and ToA estimator is proposed by fusing information from multiple received beams based on a novel beam-selection method. In addition, the theoretical performance limits are derived and compared to those obtained using the digital BFs. The cascaded framework is completed with the second-stage positioning solution in a similar manner as in the case of digital BFs. The performance of both frameworks is evaluated and analyzed in various scenarios using extensive computer simulations relying on the latest 5G NR numerology and a ray-tracing tool. Overall, this thesis provides valuable insights into practical positioning algorithms and their performance when relying solely on the 5G NR networks and available signalling therein. The obtained results in this thesis indicate that the envisioned sub-meter positioning accuracy is technically feasible using NR-based solutions

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

The Fifteenth Marcel Grossmann Meeting

The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity