Efficiency characterisation of multi-port antennas

A simple radiation efficiency metric is introduced to include the effects of non-ideal source/receiver impedances. The features of this parameter are highlighted and its compact formula is derived. The notion of mean matching efficiency is established. Simulations prove that this matching efficiency is quite useful in a quick estimation of diversity performance of multi-port antennas in rich isotropic multipath environments

LTE MIMO throughput measurement method for characterization of multi-antenna terminal performance

This paper presents experiences and results from LTE MIMO throughput measurements of a USB dongle in a reverberation test system. The measurements are performed with the dongle itself and also when it is connected to external diversity antennas with high and low correlation. Three different maximum bit rates are used, 59, 70 and 81 Mbps. The results illustrate that it is possible to separate a good antenna design from a bad from reverberation chamber measurements. Also, the effect of using a laptop test fixture, or a laptop dummy, instead of having the host computer present in the chamber, is demonstrated. It is shown that the noise induced by the host computer degrades the performance of the dongle

Closed-form design equations for decoupling networks of small arrays

Small element spacing in compact arrays results in strong mutual coupling between the array elements. A decoupling network consisting of reactive cross-coupling elements can alleviate problems associated with the coupling. Closed-form design equations for the decoupling networks of symmetrical arrays with two or three elements are presented

Characteristic Mode Analysis for Multiport Antennas

This thesis focuses on the research to overcome challenges in using the theory of characteristic mode (TCM) for multiport antennas. TCM is particularly useful for exploiting multiple radia tions on the same structure, making it well-suited for dealing with multiport antennas. However, when multiple characteristic modal radiation are activated, many of the previous designs lack a satisfactory frequency band coverage, and the number of antenna ports is often limited. Further more, when applying TCM to analyse the coupling in multiport antennas, the previous methods is not sufficiently clear and does not accommodate a higher number of ports. On the other hand, for a typical dual-polarized Base station (BS) antenna whose radiation pattern is more worthy of concern than coupling and the number of ports, its ground size is typically much larger than the operating wavelength, resulting in a considerable number of irrelevant characteristic modes (CMs) that can disrupt the analysis. In this thesis, several novel research approaches are proposed to overcome the aforementioned challenges and further exploit the application of TCM in multiport antennas. Firstly, a novel planar hexagonal antenna design, developed solely based on the principles of TCM, is proposed. The study centers around the degenerate characteristic mode (CM) pairs of symmetrical shape and their excitation during the design process. By harnessing a higher number of degenerate CM pairs, the proposed design achieves a satisfactory bandwidth among four ports and a satisfying port-to-port isolation. The second proposal introduces a method to evaluate the radiation energy and mutual coupling. This new perspective enables the enhancement of the operating band and isolation in arbitrary multiport antennas. As a result, the design and analysis of multiport antennas become easier. In line with this method, a four-port hexagonal antenna is later proposed. This four-port hexag onal antenna consists of a planar hexagonal plate, vertical tapered baluns, and a feeding network at the ground plane. The antenna exhibits a broadband impedance bandwidth while minimizing mutual coupling among its ports. The last contribution focuses on a dual-port antenna from a BS array. It examines the improvement of radiation performance of the antenna. Instead of the conventional TCM, the sub-structure TCM is employed to isolate the antenna unit from its ground and study the variations of its CMs as the frequency increases. The irreverent CMs are thus eliminated. Modifications have been implemented to enhance the beamwidth stability across the entire band

Directional Modulation for Compact Devices

A new directional modulation system which uses radiation pattern data for modulation encoding is proposed. The approach allows compact multiport antennas (e.g. MIMO capable antennas) to be used for directional modulation, replacing extensive arrays. The modulation weighting coefficients are calculated with a fixed, antenna specific equation, thus reducing computational complexity. The solution is intended to enhance privacy in small, battery-operated wireless devices, required for “Internet of Things” applications

Multiport Multiband Decoupling Optimization for Miniature Antennas

Multiband multiport antennas are increasingly used for wireless communications and sensing miniature devices. The equations governing the multiport multiband antennas are analyzed in this paper with the objective of drawing the design guidelines for low coupling small antennas. Those guidelines have been applied in the design and optimization of a two-port dual band small antenna of size around λ0/13 x λ0/13 at the lowest frequency. Certain coupling conditions are applied to the port loads achieving a coupling reduction of 8 dB when having a simple two-element real load. A reduction of 27 dB can be obtained when having ideal loads composed by a higher number of elements. The antenna geometry is shown together with coupling minimization results

Bayesian In-Situ Calibration of Multiport Antennas for DoA Estimation: Theory and Measurements

The direction-of-arrival (DoA) of radio waves is used for many applications, e.g. the localization of autonomous robots and smart vehicles. Estimating the DoA is possible with a multiport antenna, e.g. an antenna array or a multi-mode antenna (MMA). In practice, DoA estimation performance decisively depends on accurate knowledge of the antenna response, which makes antenna calibration vital. As the antenna surroundings influence its response, it is necessary to measure the entire device with installed antenna to obtain the installed antenna response. Antenna calibration is often done in a dedicated measurement chamber, which can be inconvenient and costly, especially for larger devices. Thus, auto- and in-situ calibration methods aim at making antenna calibration in a measurement chamber redundant. However, existing auto- and in-situ calibration methods are restricted to certain antenna types and certain calibrations. In this paper, we propose a Bayesian in-situ calibration algorithm based on a maximum a posteriori (MAP) estimator, which is suitable for arbitrary multiport antennas. The algorithm uses received signals from a transmitter, noisy external DoA observations, takes multipath propagation into account and does not require synchronization. Furthermore, we take an estimation theoretic perspective and provide an in-depth theoretical discussion of in-situ antenna calibration in unknown propagation conditions based on Bayesian information and the Bayesian Cramér-Rao bound (BCRB). Extensive simulations show that the proposed algorithm operates close to the BCRB and the achieved DoA estimation performance asymptotically approaches the case of a perfectly known antenna response. Finally, we provide an experimental validation, where we calibrate the antenna on a robotic rover and evaluate the DoA estimation performance using measurement data. With the proposed in-situ antenna calibration algorithm, DoA estimation performance is considerably improved compared to using an antenna response obtained by simulation or in a measurement chamber

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

Diversity Gains in Random Line-Of-Sight and Rich Isotropic Multipath Environment

Antenna diversity gain for theoretical as well as measured antennas is studied in two extreme environments, the rich isotropic multipath environment (RIMP) and the random line-of-sight environment. The RIMP diversity gain was previously defined based on improved fading performance, here we equivalently consider it as a metric for the cumulative improvement of the 1% worst users randomly distributed in the RIMP environment. Similarly, we consider the diversity gain in the random line-of-sight environment to be the performance improvement of the 1% of the users which receives the weakest signal relative to a theoretical Rayleigh distribution of the signal levels among the users. The random line-of-sight environment is regarded as being caused by the statistics of an ensemble of users (or terminals) with arbitrary 3D orientations