Compact Antennas for Wireless Communications and Terminals E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 267

Veröffentlichungsjahr: 2012

Beschreibung

Compact Antennas for Wireless Communications and Terminals deals with compact microwave antennas and, more specifically, with the planar version of these antennas. Planar antennas are the most appropriate type of antenna in modern communication systems and more generally in all applications requiring miniaturization, integration and conformation such as in mobile phone handsets. The book is suitable for students, engineers and scientists eager to understand the principles of planar and small antennas, their design and fabrication issues, and modern aspects such as UWB antennas, reconfigurable antennas and diversity issues.

Leseprobe

Table of Contents

Introduction

Chapter 1. General Information About Printed Antennas

1.1. Physical characteristics

1.2. Properties, limitations, and applications

1.3. Printed rectangular antenna viewed as a wide microstrip line

1.4. Manufacturing processes

1.5. Microwave substrates

Chapter 2. Transmission Line Model

2.1. Introduction

2.2. Equivalent circuit

2.3. Input impedance

Chapter 3. Cavity Model

3.1. Introduction

3.2. Formulation of the electromagnetic problem

3.3. Calculation of expressions for fields and currents of arectangular patch

3.4. Expressions for principal modes

3.5. Cartography of modal currents and associated radiation patterns

Chapter 4. Radiation of a Printed Antenna

4.1. Introduction

4.2. Modelization using two equivalent radiating slots

4.3. Calculation of the field radiated by a horizontal radiating slot

4.4. Calculation of the field radiated by the rectangular patch

4.5. Determination of the radiation pattern in the principal planes

4.6. Influence of height

4.7. Influence of the ground plane

4.8. Polarization

4.9. Directivity

4.10. Influence of the substrate on resonant frequency: parametricstudy based on antenna RCS

Chapter 5. Electrical Equivalent Circuit of a Printed Antenna

5.1. Energy considerations

5.2. Equivalent circuit

5.3. Determination of WE, WM, and B for a rectangular patch

5.4. Modeling using a tank circuit

5.5. Quality factor of an antenna

5.6. Calculation of radiation quality factor

5.7. Calculation of efficiency

5.8. Influence of surface waves on bandwidth and efficiency

Chapter 6. Feeding Circuits for Microstrip Antennas

6.1. Introduction

6.2. Direct coupling by coaxial probe

6.3. Excitation by proximity coupling

6.4. Excitation by slot coupling

Chapter 7. Circularly Polarized Antennas

7.1. Principles of circular polarization

7.2. Parasitic radiation — degradation of circular polarization

7.3. Patch fed by single or dual excitation

7.4. Sequential array

7.5. Spiral and quadrifilar helix antennas

7.6. Conclusion

Chapter 8. Wideband Antennas

8.1. Multiresonant antennas

8.2. Traveling wave antennas

8.3. Frequency independent antennas

8.4. Ultra‐wideband antennas

8.5. Conclusion

Chapter 9. Miniature Antennas

9.1. Introduction

9.2. Which types of antennas should be used for integration?

9.3. Integration limits in a finite volume

9.4. Resonant antennas in fundamental mode

9.5. Bulk reduction techniques

9.6. Multiresonant antennas

9.7. Synthesis and discussion

Chapter 10. Reconfigurable Antennas

10.1. Introduction

10.2. Basic topologies and constraints

10.3. Switched components: available technologies

10.4. Frequency reconfigurable antennas (FRAs)

10.5. Introduction to RAs in terms of polarization andradiation pattern

10.6. Polarized reconfigurable antennas (PRAs)

10.7. Radiation pattern reconfigurable antennas (RPRAs)

Chapter 11. Introduction to Antenna Diversity

11.1. Benefits of antenna diversity

11.2. Performance of multiantenna systems

11.3. Multiantenna systems

11.4. Conclusion and looking toward MIMO

Bibliography

List of Authors

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

ISTE Ltd

John Wiley & Sons, Inc

27–37 St George’s Road

111 River Street

London SW19 4EU

Hoboken, NJ 07030

UK

USA

www.iste.co.uk

www.wiley.com

© ISTE Ltd 2011

The rights of Jean-Marc Laheurte to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Compact antennas for wireless communications and terminals : theory and design / edited by Jean-Marc Laheurte.       p. cm.   Includes bibliographical references and index.   ISBN 978-1-84821-307-4   1. Antennas (Electronics)--Design and construction. 2. Wireless communication systems. I. Laheurte, Jean-Marc.   TK7871.6.C626 2011   621.384′135--dc23

2011021212

British Library Cataloguing-in-Publication Data A CIP record for this book is available from the British Library ISBN 978-1-84821-307-4

Introduction

This publication covers microwave antennas and more specifically planar versions, which are the types of antenna preferred at microwave frequencies in modern integrated communication systems. We see variants of these in everyday life, hidden away in portable telephones, mobile phone base stations, electronic tags, or even portable computers. More generally, we see them in all applications requiring miniaturization and/or a fixed support structure, such as telephone casings. In terms of this publication, we are therefore not including reflector antennas, antenna arrays, or more generally directional antennas that occupy a surface or volume much greater than the wavelength.

Written by a collective of specialist engineers and research professors, this book is aimed at engineers and researchers who want to:

– understand the principles of planar and/or small volume antennas used in modern communication systems;

– comprehend the problems of design and manufacture;

– define the constraints and limitations presented by the antenna within the body of the communication system.

Chapter 1 deals with the physical characteristics of printed antennas (dielectric support, metallization), manufacturing techniques, and areas of application.

Chapters 2 and 3 describe the so-called transmission line and cavity models, respectively, of printed antennas. These two models provide complementary physical interpretations of the basic, usually rectangular geometry of antennas. These interpretations will apply to more complex yet short depth geometries. Also we will restrict ourselves to rectangular geometries, to limit the amount of analysis.

Chapter 4 deals with radiation from the rectangular planar antenna from the point of view of equivalent magnetic currents. We will examine in particular the influence on the characteristics of the radiation pattern, from fundamental parameters such as the thickness and dielectric permittivity of the substrate or the dimensions of the ground plane. We will also see that the calculation of the wave backscattered by an antenna illuminated by a plane wave enables the resonance frequency of the antenna to be determined.

Chapter 5 describes in depth the rationale leading to an electric RLC circuit model for this type of antenna. The concepts of bandwidth and efficiency are tackled from the quality factor of the equivalent resonant circuit. The influence of physical (permittivity of, and losses in the substrate) and geometrical parameters on these measurements is highlighted.

The different methods of powering antennas are described in Chapter 6 while emphasizing the concept of coupling between feeding circuit and radiating sections. Power by slot coupling is specifically examined, since it possesses a number of geometric parameters for adjusting the matching which are greater than excitation by direct coupling.

Chapter 7 examines in detail circular polarization, while defining primarily the base concepts before introducing several types of circular polarization antennas. On the one hand, we have simple, purely planar antennas with one or two ports, whose performance is improved with the principle of sequential rotation. On the other hand, we have spirals and quadri-helix antennas, whose performance in terms of bandwidth or purity of polarization over wide coverage areas, are much superior.

Chapter 8 deals with broadband and partially with multiband antennas. In the context where spread spectrum modulations are assuming increasing importance, the need to create antennas that are at the same time broadband and miniaturized has given rise to a great many studies in recent years. This chapter summarizes not only these, while attempting to describe the general design philosophy, but also the practical limitations of production, linked notably to the reduced size of the ground plane.

Chapter 9 is an introduction to the world of miniaturized antennas. This vast topic is the subject of specialist publications, where the problem of the antenna presenting an optimized efficiency and bandwidth over a given volume is handled both theoretically and experimentally. This chapter will instead attempt to reveal the base concepts that enable us, from resonant canonical patch or half-wave dipole antennas, to reduce the dimensions of antennas in line with the most common planar inverted-F antenna (PIFA), IFA, or wire-plate structures. The principle strategies in miniaturization (addition of short circuits, introduction of slits) are extensively detailed.

Chapter 10 deals with the reconfigurability of antennas by active elements. This concerns antennas having the capacity to electronically reconfigure one or more of their characteristics (pattern, polarization, impedance). The object here is twofold. In the context of terminal miniaturization, it becomes possible to change the radiation characteristics and the working frequency of a structure through the switching or selection of feeding ports, in other words to produce the equivalent of several colocalized antennas. In the context of antenna diversity, we suggest some intelligent structures that are either opposing or adaptable to an evolving environment. Variations in the environment might result from signal fadings linked to multipaths in towns, disturbances due to the human body near to the terminal or quite simply changes in communication standards.

Chapter 11 is a didactic introduction to the diversity of antennas used more and more in modern communication systems. Using the base theory of multipath channels, the author emphasizes the advantages of multiantenna systems to combat fadings, while notably introducing the concept of diversity gain. The impact of the correlation and imbalance between the received signals on the link quality is underlined. We also state a fundamental relationship between the coefficient correlation and the coupling S-matrix between antennas. This chapter includes the study of produced and tested multiantenna systems.

Chapter 1General Information About Printed Antennas1

1.1. Physical characteristics

The basic printed antenna consists of a thin layer of metal (patch) positioned over a ground plane, both being etched on the two sides of a substrate of permittivity εr and thickness h (Figure 1.1). Typically, h ≪ λ0 and 0.003λ0 < h < 0.05λ0. The length L of the patch is of the order of , where εeff is the relative permittivity of the patch.

The terms printed, plated, or patch antenna are used interchangeably to describe planar antennas produced using photolithographic techniques. Note that there are planar antennas that are not produced using these techniques. For example, this is the case with PIFA antennas or their variants in 1 GHz mobile telephony, the substrate here being made up of air with metallic parts produced using copper or aluminum foil that has been folded and machined (Figure 1.2).

Planar antennas can equally be produced under clean conditions over silicon (Figure 1.3) or glass substrates using microtechnological manufacturing processes. Because of the given antenna dimensions (of the order of 1 cm), the manufacturing costs and patterning tolerances, the applications planned are typically beyond the Ka band (about 20 GHz).