Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Engineering Parallel Transmit/Receive Radio-Frequency Coil Arrays for Human Brain MRI at 7 Tesla

Magnetic resonance imaging is widely used in medical diagnosis to obtain anatomical details of the human body in a non-invasive way. Clinical MR scanners typically operate at a static magnetic field strength (B0) of 1.5T or 3T. However, going to higher field is of great interest since the signal-to-noise ratio is proportional to B0. Therefore, higher image resolution and better contrast between the human tissues could be achieved. Nevertheless, new challenges arise when increasing B0. The wavelength associated with the radio-frequency field B1+ has smaller dimensions - approx. 12 cm for human brain tissues - than the human brain itself (20 cm in length), the organ of interest in this thesis. The main consequence is that the transmit field distribution pattern (B1+) is altered and the final MR images present bright and dark signal spots. These effects prevent the ultra-high field MR scanners (>= 7T) to be used for routine clinical diagnosis. Parallel-transmit is one approach to address these new challenges. Instead of using an RF coil connected to a single power input as it is commonly done at lower magnetic fields, multiple RF coils are used with independent power inputs. The subsequent distinct RF signals can be manipulated separately, which provides an additional degree of freedom to generate homogeneous B1+-field distributions over large or specific regions in the human body. A transmit/receive RF coil array optimized for whole-brain MR imaging was developed and is described in this thesis. Dipoles antennas were used since they could provide a large longitudinal (vertical axis-head to neck) coverage and high transmit field efficiency. Results demonstrated a complete coverage of the human brain, and particularly high homogeneity over the cerebellum. However, since the receive sensitivity over large field-of-views is related to the number of channels available to detect the NMR signal, the next work was to add a 32-channel receive loop coil array to the transmit coil array. The complete coverage of the human brain was assessed with a substantial increase in signal-to-noise compared to the transmit/receive dipole coil array alone. Moreover, acquisition time was shortened since higher acceleration factors could be used. To optimize the individual RF fields and generate an homogeneous B1+-field, a method was developed making use of the particle-swarm algorithm. A user-friendly graphical interface was implemented. Good homogeneity could be achieved over the whole-brain after optimization with the coil array built in this study. Moreover, the optimization was shown to be robust across multiple subjects. The last project was focused on the single transmit system. Local volume coils (single transmit) present pronounced transmit field inhomogeneities in specific regions of the human brain such as the temporal lobes. A widely used approach to address locally these challenges is to add dielectric pads inside the volume coils to enhance the local transmit field efficiency. It was shown in this thesis that constructing dedicated surface coils is a valuable alternative to the dielectric pads in terms of transmit field efficiency and MR spectroscopy results. Two RF coil setups were developed for the temporal and frontal lobes of the human brain, respectively. This thesis provides extensive insight on MR engineering of RF coils at ultra-high field and the potential of parallel-transmit to address the future needs in clinical applications

Systematic Design of Multiport Antennas for MIMO-enabled Mobile Wireless Terminals

Mobile wireless communication systems have undergone a tremendous development in the past decade. One of the major advancements is the widespread use of MIMO transmission schemes beginning with the introduction of the 3rd Generation Partnership Project (3GPP) standard LTE and being extended in LTE Advanced. So as to support MIMO transmission schemes mobile terminals must be equipped with multiport antenna systems. The term refers to an arrangement of two or more antenna elements operating in the same frequency range and mounted on the same mobile wireless platform. Reduced volume per antenna element and strong interaction between all antenna elements are major design challenges and require for new systematic design approaches beyond classical single antenna design. The ongoing miniaturization of mobile terminals, the extension of the mobile spectrum and in particular the opening of new mobile communication bands at the lower end of the spectrum exacerbate these challenges. Design and characterization of multiport antennas have therefore become subject of high interest and of numerous research projects in both academia and industry. This dissertation contributes to the development of systematic design procedures for multiport antennas with emphasis on accounting for the restrictions and side conditions which apply when designing multiport antennas for actual consumer equipment. The dissertation has developed along an industry funded research project, with a focus on electrically small devices where antenna design is constantly faced with fundamental physical limits. Chapter 1 gives an overview of the state of the art in antenna characterization and design techniques applicable to multiport antennas for MIMO. Chapter 2 introduces into the analysis of multiport antennas in terms of their radiation modes. Modal analysis, based on spectrum of the radiation matrix, allows for unambiguous characterization of a multiport antenna by means of invariant properties. Modal descriptive quantities are defined which are basic to the design approach followed in this dissertation. Analyzing a multiport antenna with respect to its radiation modes is possible only after a design concept has been conceived. More fundamental from a design point of view is the question for the space of feasible radiation modes and their realization under the constraint of a given chassis form factor. Chapter 3 addresses this question based on the theory of characteristic modes for conducting bodies. The relevant properties of characteristic modes on the chassis of mobile terminals are reviewed. The excitation of characteristic modes by means of capacitive and inductive coupling elements is investigated in detail. Finally, a systematic design approach for multiport antennas is presented in which the antenna’s radiation modes are constructively derived from the usable characteristic chassis modes. Chapter 4 deals with design of matching networks for N-port antennas. Starting from the general expression for the scattering matrix of an ideal 2N-port matching network different topologies and alternative implementations are discussed. As a solution of particular interest in cases where some radiation modes feature insufficient bandwidths, special attention is given to systematic design of MDN which maps radiation modes to external ports of the antenna system. Chapter 5 focuses on the particular problems encountered in the design of antenna systems for extremely small mobile wireless terminals. After a review of applicable fundamental limits bandwidth estimation and approaches to maintain a decent total efficiency are discussed. The combination of electrical switching in the antenna structure with electrical tuning in an external matching network is suggested in this context. The DL-MIMO concept is introduced as a system level measure to cope with insufficient bandwidth. The different aspects are exemplified with the design of a 2-port MIMO antenna for a USB dongle. Chapter 6 describes in detail design, fabrication and measurement of four antenna prototypes. The validity of the design approach described in the previous chapters is confirmed. In conclusion, a systematic design approach, which combines the theory of characteristic chassis modes for conducting bodies with modal analysis of a multiport antenna, i.e. considers the spectrum of its radiation matrix is presented. The approach is successfully applied to a number of practically relevant design problems. The design technique permits identification of near optimum antenna solutions which approach the fundamental limits of attainable bandwidth and total efficiency.Systematischen Entwurf von Multiport-Antennen für MIMO-fähigen Mobilfunkendgeräte Die Mobilkommunikation hat in den letzten Jahren eine enorme Entwicklung durchlaufen. Eine der wesentlichen technischen Weiterentwicklungen ist der Übergang zu MIMO Übertragungsverfahren, in großem Maßstab beginnend mit der Einführung des 3GPP Standards LTE und in grÖßerem Umfang noch im zukünftigen LTE-Advanced. Mobile Endgeräte müssen dazu mit Mehrtorantennen ausgestattet sein. Der Begriff Mehrtorantenne bezeichnet eine Anordnung von zwei oder mehr Antennenelementen, die im gleichen Fequenzbereich betrieben werden und auf einer gemeinsamen Plattform angeordnet sind. Die Verringerung des je Antennenelement zur Verfügung stehenden Volumens und die starke Kopplung zwischen den Antennenelementen führen auf neue Herausforderungen für den Entwurf. Neue, systematische Entwurfsmethoden jenseits der klassischen Methoden für den Entwurf von Einzelantennen sind gefordert. Die fortschreitende Miniaturisierung mobiler Endgeräte, die Erweiterung des für den Mobilfunk genutzten Spektrums und insbesondere die Öffnung neuer Bander am unteren Ende des Spektrums für den Mobilfunk verschärfen die Anforderung an die Entwurfsmethodik. Entwurf und Charakterisierung von Mehrtorantennen sind deswegen heute Themen von großem Interesse und Gegenstand zahlreicher industrieller und akademischer Forschungsprojekte. Die vorliegende Dissertation liefert einen Beitrag zur Entwicklung systematischer Entwurfsverfahren für Mehrtorantennen unter besonderer Berücksichtigung der Einschränkungen und Randbedingungen die beim Entwurf von kommerziellen Endgeräten vorliegen. Zahlreiche Fragestellungen ergaben sich aus einem vom Verfasser bearbeiteten industriellen Forschungs- und Entwicklungsprojekt mit Schwerpunkt auf elektrisch kleinen Endgeräten, bei denen der Entwurf stets mit fundamentalen physikalischen Schranken konfrontiert ist. Kapitel 1 gibt einen Überblick über den Stand der Technik auf dem Gebiet des Entwurfs und der Charakterisierung von Mehrtorantennen für MIMO Anwendungen. Kapitel 2 führt in die Analyse von Mehrtorantennen mit Hilfe ihrer Strahlungsmoden ein. Die modale Betrachtung auf Grundlage des Spektrums der Strahlungsmatrix gestattet es, Mehtorantennen mit Hilfe ihrer invarianten Eigenschaften eindeutig zu charakterisieren. Es werden die modalen Beschreibungsgrössen definiert auf denen der in dieser Arbeit verfolgte Entwurfsansatz basiert. Die Strahlungsmoden einer Mehtorantenne können jedoch erst betrachtet werden, wenn ein Entwurf bereits vorliegt. Die vom Standpunkt der Entwurfsmethodik wichtigere Frage ist die nach Raum der unter den Einschränkungen eines gegebenen Geräte-Formfaktors realisierbaren Strahlungsmoden. Sie wird in Kapitel 3 auf Grundlage der Theorie Charakteristischer Moden leitender Körper behandelt. Die relevanten Eigenschaften charakteristischer Moden auf dem Gehäuse elektrisch kleiner mobiler Endgeräte werden betrachtet. Die Anregung charakteristischer Moden mit Hilfe von kapazitiven und induktiven Koppelelementen wird ausführlich untersucht. Abschließend wird ein Entwurfsansatz für Mehtorantennen beschrieben, in welchem die Strahlungsmoden der Antenne konstruktiv aus den nutzbaren charakteristischen Moden des Gehäuses abgeleitet werden. In Kapitel 4 werden Anpassnetzwerke für N-Tor Antennen behandelt. Ausgehend von der allgemeinen Formulierung für die Streumatrix des benötigten 2N-Tor Netzwerkes werden verschiedene Topologien und Realisierungsalternativen diskutiert. Gesondert betrachtet werden noch einmal MDNs, welche die Strahlungsmoden einer Mehtorantenne unmittelbar auf die Speisetore abbilden, da sie in Falle unzureichender modaler Bandbreiten, von besonderem Interesse sind. Kapitel 5 fokussiert auf die besonderen Probleme bei beim Entwurf extrem kleiner Antennensysteme. Nach Betrachtung in die maßgeblichen physikalischen Beschränkungen werden die Abschätzung erreichbarer Bandbreiten und Maßnahmen zur Sicherstellung eines akzeptablen Wirkungsgrades diskutiert. Vorgeschlagen wird in diesem Zusammenhang die Kombination von elektrisch rekonfigurierbaren Antennenstrukturen mit elektrisch abstimmbaren Anpass-Netzwerken. Die verschiedenen Aspekte werden am Beispiel des Entwurfs eines 2-Tor MIMO Antennensystems für einen USB Dongle erläutert. pKapitel 6 beschreibt im Detail den Entwurf, die Herstellung und die messtechnische Charakterisierung vier unterschiedlicher Prototypen von Mehrtorantennen. Anhand der Beispiele wird der in den vorherigen Kapiteln entwickelte Entwurfsansatz validiert. Insgesamt wird mit dieser Arbeit ein systematischer Entwurfsansatz vorgeschlagen, der auf der Kombination der Theorie charakteristische Moden leitender Körper mit der modalen Analyse von Mehrtorantennen, d.h. der Betrachtung des Spektrums der Strahlungsmatrix aufbaut. Der Ansatz wird erfolgreich auf eine Reihe praktisch relevanter Entwurfsaufgaben angewandt. Er führt auf ein systematisches Entwurfsverfahren, das es gestattet, Lösungen in der Nähe der physikalischen Grenzen für die erreichbare Bandbreite und den Wirkungsgrad aufzufinden

Circuit-Theoretic Physics-Based Antenna Synthesis and Design Techniques for Next-Generation Wireless Devices

Performance levels expected from future-generation wireless networks and sensor systems are beyond the capabilities of current radio technologies. To realize information capacities much higher than those achievable through existing time and/or frequency coding techniques, an antenna system must exploit the spatial characteristics of the medium in an intelligent and adaptive manner. This means that such system needs to incorporate integrated multi-element antennas with controlled and adjustable performances. The antenna configuration should also be highly miniaturized and integrated with circuits around it in order to meet the rigorous requirements of size, weight, and cost. A solid understanding of the underlying physics of the antenna function is, and has always been, the key to a successful design. In a typical antenna design process, the designer starts with a simple conceptual model, based on a given volume/space to be occupied by the antenna. The design cycle is completed by the antenna performing its function over a range of frequencies in some complex scenarios, i.e., packaged into a compact device, handled in different operational environments, and possibly implanted inside a human/animal body. From the conceptual model to the actual working device, a large variety of design approaches and steps exist. These approaches may be viewed as simulation-driven steps, experimental-based ones, or a hybrid of both. In any of these approaches, a typical design involves a large amount of parametric/optimization steps. It is no wonder, then, that due to the many uncertainties and ‘unknowns’ in the antenna problem, a final working design is usually an evolved version of an initial implementation that comes to fruition only after a considerable amount of effort and time spent on “unsuccessful” prototypes. In general, the circuit/filter community has enjoyed a better design experience than that of the antenna community. Designing a filter network to meet specific bandwidth and insertion loss is a fairly well-defined procedure, from the conceptual stages to the actual realization. In view of the aforementioned, this work focuses on attempting to unveil some of the uncertainties associated with the general antenna design problem through adapting key features from the circuit/filter theory. Some of the adapted features include a group delay method for the design of antennas with a pre-defined impedance bandwidth, inverter-based modeling for the synthesis of small-sized wideband antennas, and an Eigen-based technique to realize multi-band/multi-feed antennas, tunable antennas, and high sensitivity sensor antennas. By utilizing the proposed approaches in the context of this research, the design cycle for practical antennas should be significantly simplified along with various physical limitations clarified, all of which translates to reduced time, effort, and cost in product development.4 month

Impedance Transformers

Non

Modale Analysemethode für die Entwicklung von kleinen Antennen

The Theory of Characteristic Modes (TCM) has proved itself well in antenna design even in the recent years. A large number of applications has been presented by other authors, in which the TCM has been utilized. In this dissertation, the common theory is extended with new numerical techniques suitable for the design of small antennas. Eigenvalue tracking as a fundamental numerical problem, which arises from the early mode analysis, is discussed. The degenerated mode effect is presented and an explanation is given as to where it comes from and how it affects the tracking concept. A new algorithm is presented to generate differential eigenvalue curves and to compensate for the degenerated mode effect. The modal source reconstruction is an additional technique, which is used to predict the mode contribution from a simplified structure. This technique allows utilization of the TCM with other not Method of Moments based solver under the assumption that the simplified structures carries almost the same chassis modes as the real structure. Furthermore, the lumped impedance matching networks are treated in the mode analysis. The influence of such lumped networks on the characteristic modes is investigated and the modal efficiency is defined. The definition of the modal admittances and impedances are given and evaluated for inductive and capacitive coupling elements. Equivalent circuit models are presented and evaluated for these types of coupling elements for generic examples. The problem of a useful interpretation of the dielectric modes and their eigenvalue are discussed and evaluated for dielectric resonator antennas (DRAs). Finally, the combined mode excitation concept is presented and evaluated for small terminals. This concept is used as a basis to integrate antennas into a hand held device. The experiences are used to develop the proposed concept further and to integrate the antennas into the rearview mirror of a vehicle.Die Antennenentwicklung auf Basis der Theorie der Charakteristischen Moden (TCM) hat sich vor allem in den letzten Jahren rasant weiterentwickelt. In dem Hauptfokus dieser Dissertation ist die theoretische und numerische Erweiterung der Theorie, welche für die Entwicklung von kleinen Antennen besonders geeignet sind. Das Problem der Eigenwertverfolgung ist ein seit langem bekanntes Problem, welches bis heute nicht ausreichend gelöst ist. Das Problem der entarteten Moden wird präsentiert und es wird ausführlich erklärt, woher das Problem kommt und wie dieser die Verfolgung der Moden beeinflusst. Aufbauend auf diese Untersuchung wird ein neues Verfahren präsentiert, welches das Problem der entarteten Moden kompensiert und die Verfolgung der Eigenwerte entscheiden verbessert. Die Vorhersage der modalen Stromverteilung auf Basis des modalen Fernfeldes ist eine neue Methode, um nicht Momenten basierte Solver in die TCM einzubeziehen. Dieses Konzept basiert auf der Annahme, dass eine vereinfachte Struktur die gleichen Moden unterstützt, wie das komplexere Model, mit allen darin enthaltenen Details. Weiterhin werden konzentrierte Netzwerke in die Modenberechnung einbezogen, um so den Einfluss der reaktiven Komponenten zu beurteilen. Äquivalente Ersatzschaltungen werden entwickelt und für einige in der Antennentechnik übliche Beispiele validiert. Das Problem der sinnvollen Interpretation der dielektrischen Moden wird aufgegriffen und diskutiert. Abschließend wird ein neues Konzept der kombinierten Anregung der Moden präsentiert und speziell für die Antennenintegration in kleine mobile Plattformen diskutiert. Dieses Konzept wird für ein kleines mobiles Endgerät aufgebaut und messtechnisch verifiziert. Aufbauend auf dieser Entwicklung wird das hier präsentierte Konzept weiterentwickelt und es werden mehrere Antennen in einem Innenspiegel eines Autos integriert

Simplified equivalent modelling of electromagnetic emissions from printed circuit boards

Characterization of electromagnetic emissions from printed circuit boards (PCBs) is an important issue in electromagnetic compatibility (EMC) design and analysis of modern electronic systems. This thesis is focused on the development of a novel modelling and characterization methodology for predicting the electromagnetic emissions from PCBs in both free space and closed environment. The basic idea of this work is to model the actual PCB radiating source with a dipole-based equivalence found from near-field scanning. A fully automatic near-field scanning system and scanning methodology are developed that provide reliable and sufficient data for the construction of equivalent emission models of PCB structures. The model of PCB emissions is developed that uses an array of equivalent dipoles deduced from magnetic near-field scans. Guidelines are proposed for setting the modelling configuration and parameters. The modelling accuracy can be improved by either improving the measurement efforts or using the mathematical regularization technique. An optimization procedure based on genetic algorithms is developed which addresses the optimal configuration of the model. For applications in closed environments, the equivalent model is extended to account for the interactions between the PCB and the enclosure. The extension comprises a dielectric layer and a ground plane which explicitly represent the necessary electromagnetic passive properties of a PCB. This is referred to as the dipole-dielectric-conducting plane (DDC) model and provides a completely general representation which can be incorporated into electromagnetic simulation or analysis tools. The modelling and characterization methodology provides a useful tool for efficient analysis of issues related to EMC design of systems with PCBs as regards predicting electromagnetic emissions in both free space and closed environment. The proposed method has significant advantages in tackling realistic problems because the equivalent models greatly reduce the computational costs and do no rely on the knowledge of detailed PCB structure

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin