Small Antenna Handbook E-Book

Robert C. Hansen

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

Seitenzahl: 456

Veröffentlichungsjahr: 2011

Beschreibung

Now in an completely revised, updated, and enlarged Second Edition, Small Antennas in Portable Devices reviews recent significant theoretical and practical developments in the electrically small antenna area. Examining antenna designs that work as well as those that have limitations, this new edition provides practicing engineers and upper level and graduate students with new information on: work on improving bandwidth using spherical helix dipoles; work on electromagnetically coupled structures; exact derivation of the Q for electrically small antennas for both the TE and TM modes; and a new simplified Q formula.

Leseprobe

Copyright © 2011 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:

Hansen, Robert C.

Small antenna handbook / R.C. Hansen and R.E. Collin.

p. cm.

Includes bibliographical references and index.

ISBN 978–0–470–89083–7

1. Antennas (Electronics) 2. Miniature electronic equipment. I. Collin, Robert E. II. Title.

TK7871.6.H35157 2011

621.382'4–dc23

2011013601

oBook ISBN: 9781118106860

ePDF ISBN: 9781118106839

ePub ISBN: 9781118106853

This book is dedicated to these intrepid warriors against nut-house antennas

Dick Adler

Jack Belrose

Ben Dawson

Jim Hatfield

Larry Hurzon

Rick Ridgley

Robert Emanuel Collin 1928-2010

Bob Collin was born in Alberta, Canada. He received the B.Sc. degree in engineering physics from the University of Saskatchewan in 1951. He attended Imperial College in England for graduate work and obtained the Ph.D. degree in electrical engineering from the University of London in 1954. From 1954 to 1958, he was a Scientific Officer at the Canadian Armament Research and Development Establishment, where he worked on guided missile antenna, randome, and radar system evaluations. He joined the Electrical Engineering Department at Case Institute of Technology in 1958, now Case Western Reserve University. During his tenure there, he served as Chairman of the Department of Electrical Engineering and Applied Physics for five?years and as Interim Dean of Engineering for two years. He has been an Invited Professor at Catholic University in Rio de Janeiro, at Telebras Research Center, Campinas, Brazil, and at Beijing University, People's Republic of China. He was also Distinguished Visiting Professor at the Graduate School, The Ohio State University, during the 1982–1983 academic year.

Professor Collin authored more than 150 technical papers and 5 books. Two books, Field Theory of Guided Waves and Foundation of Microwave Engineering, became classics and were republished by IEEE Press.

He was a fellow of IEEE, a member of URSI Commission B, and a member of the Geophysical Society. Other honors include the Dickman Award from Case Western Reserve University for distinguished graduate teaching, the IEEE APS Distinguished Career Award (1992), the IEEE Schelkunoff Prize Paper Award (1992), and the IEEE Electromagnetics Award (1998). In 1990, Professor Collin was elected to the National Academy of Engineering. His insight into the mathematics of electromagnetics was unparalleled.

Books by R. C. Hansenr

Microwave Scanning Antennas (3 volumes)

Significant Phased Array Papers

Geometric Theory of Diffraction

Moment Methods in Antennas and Scattering

Phased Array Antennas, second edition

Electrically Small, Superdirective, and Superconducting Antennas

Books by R. E. Collin

Antenna Theory, with F. J. Zucker (2 volumes)

Field Theory of Guided Waves, second edition

Foundations of Microwave Engineering, second edition

Antennas and Radiowave Propagation

Principles and Applications of Electromagnetic Fields, with R. Plonsey

Preface

Harold Wheeler, in his classic 1947 papers (Wheeler, 1947a, 1947b), created the field of electrically small antennas (ESA), although, as shown in the history (Appendix A), the early antennas were all electrically small. This field has long been important for frequencies below roughly 1 GHz, where a half-wavelength is about 6 in. These electrically small antennas have characteristics in common that limit performance: low radiation resistance, high reactance, low efficiency, narrow bandwidth, and increased loss in the matching network. Most of these limitations are shared by two other classes of antennas: superdirective antennas and superconducting antennas.

The original intent was to update Electrically Small, Superdirective, and Superconducting Antennas with a second edition. Sufficient material became available to broaden the scope of that book; the result is this book with a new title. This book provides mathematical foundations for important topics including ENG shells, ESA with or cores, including lossy cores, and focused/subwavelength imaging.

Chapter 1 contains detailed electromagnetic derivations of Chu and Thal formulations, formulas for when or cores are used, and effects of loss on . Finally, work on fundamental limitations using spheroids instead of the radian sphere is covered. Chapter 2 is a treatise on bandwidth and matching, and Foster's reactance theorem. Precise data are given for Fano's matching limitations and bandwidth improvement. The effects of loss in matching circuits and cables on VSWR are shown. The relatively new field of non-Foster matching is next discussed. Finally, performance of a short monopole that is matched is compared with that of monopole with high-impedance preamp. Chapter 3 provides updated coverage on canonical antennas: dipoles, loops, self-resonant ESA, PIFA, and dielectric resonator antennas. A comparison is made of Q of various antennas with the Chu–Thal fundamental limitation. In Chapter 4 are presented six ideas that are clever but with performance numbers that are poor. Eighteen nutty antenna ideas are detailed in Chapter 5; the list keeps growing! Chapter 6 on superdirective antennas has been updated with recent data on the use of self-resonant elements. These allow modest supergain but bandwidth and tolerance limitations remain. Also included is new material on maximum directivity of arrays. The last chapter, on superconducting antennas, has been updated with new delay line data. The earlier conclusion that superconductors should be considered for the matching network, but not the antenna, still holds.

A world history of ESA is presented in Appendix A. Antenna terms important to ESA are defined in Appendix B. Appendix C contains a paper by Karawas and Collin (2008) on NIM shells enclosing an ESA dipole. The analytical errors associated with perfect lenses and subwavelength focusing are treated in detail by Collin (2010) in Appendix D. Each chapter includes extensive references. An overall subject index and an author index are provided at the end of the book.

We antenna engineers have done what is possible by rearranging the wires; future significant advances will come through the use of new low-loss magnetic materials and through the use of circuits to compensate for impedance deficiencies.

R. C. Hansen and R. E. Collin

References

Collin, R. E. Frequency Dispersion Limits in Veselago Lens, Prog. Electromagnetics Res. B, Vol. 19, 2010, pp. 233–261.

Karawas, G. K. and Collin, R. E. Spherical Shell of ENG Material Surrounding a Dipole Antenna, IEEE MILCOM, 2008, pp. 1–15.

Wheeler, H. A. Fundamental Limitations of Small Antennas. Proc. IRE, Vol. 35, December 1947a, pp. 1479–1484.

Wheeler, H. A. A Helical Antenna for Circular Polarization. Proc. IRE, Vol. 35, December 1947b, pp. 1484–1488.

Chapter 1

Quality Factors of ESA

1.1 Introduction

In a 1947 paper, Harold Wheeler defined an electrically small antenna (ESA) as an antenna that could be enclosed within a radian sphere (Wheeler, 1947). The radian sphere was a sphere of radius equal to , where is the wavelength. The antennas used by Marconi and Fessenden in the early years of wireless telegraphy were electrically small antennas even though they were very large physical structures, often involving wires strung as an inverted fan or cone from masts several hundred feet tall. These antennas were electrically small antennas since in order to achieve long-distance transmission the wavelengths used, typically greater than 3000 m, were much longer than the antenna heights. These electrically small antennas were characterized by a very low radiation resistance and a large capacitive input reactance. The purpose of the large inverted fans and cones was to increase the antenna capacitance and thus reduce the capacitive reactance. Wheeler introduced the radiation power factor (RPF) as a figure of merit for these electrically small antennas. He considered two basic antenna types: the magnetic dipole or loop antenna consisting of a solenoid coil with N turns, length b, and radius a; and a short electric dipole antenna consisting of a thin wire of length b and with capacitive loading at each end by means of circular conducting disks of radius a. The radiation power factor was defined as the ratio of the radiation resistance to the reactance of the antenna. For the solenoid loop antenna, the radiation resistance is given by . An approximate expression for the inductance of the solenoid coil is . For the small electric dipole, the radiation resistance is given by and the capacitance between the two circular plates is when the fringing effects are neglected. From these expressions, we can calculate the radiation power factors, for the magnetic dipole and for the electric dipole, as follows:

(1.1a)

(1.1b)

Wheeler modified Equation 1.1 by magnetic and electric shape factors derived from statics. For ESA, the radiation power factors are very small. Also see Wheeler (1975).

Wheeler's radiation power factors are related to the Q parameter introduced by Kenneth S. Johnson, an authority on wire transmission at Bell Telephone Laboratories. Initially, Johnson used the symbol K to represent the ratio of the inductive reactance to the resistance of a coil, . In 1920, while working on wave filters, invented by G. A. Campbell, he replaced the symbol K by the symbol Q and introduced the lowercase symbol q for the analogous quantity for a capacitor C, where G is the parallel conductance of a capacitor (called condenser in those days). Later on in 1927 he used Q for both in his U.S. Patent No. 1,628,983. His introduction of this symbol was adopted by most people working with tuned circuits in radio receivers in the early days of radio broadcasting.

It is easily shown that the response of a tuned circuit, consisting of a parallel or series connection of an inductor and a capacitor, is reduced by the factor when the circuit is detuned by a fractional amount , provided the Q is equal to 10 or more. Thus, 1/Q is the 3 dB bandwidth (BW) of the tuned circuit. If a resistive load is connected across the tuned circuit such that a maximum amount of power can be obtained from the circuit, the Q of the loaded circuit is reduced by a factor of 2 and the 3 dB bandwidth is increased by a factor of 2. Tuned circuits with high values of Q were needed in order to achieve high selectivity in the tuned radio frequency radios. This led to extensive efforts to design radio frequency coils with low loss resistance. During the World War II years, the Q became widely used to describe the sharpness of the resonance curve of both electric and mechanical resonators such as microwave cavities, quartz crystal resonators, and so on. If we have a tuned circuit with a capacitor C in parallel with an inductor L, it is known that the resonant frequency of the circuit is given by and that at resonance the time-averaged energy stored in the capacitor is equal to that in the inductor. If the inductor has a series resistance and the current in the inductor is , then the average energy stored in the magnetic field around the inductor is given by and the average power dissipated in the resistor is . When we introduce these into the definition of , as used by Johnson, we can express in the form