ELECTROMAGNETICS EXPLAINED A HANDBOOK FOR WIRELESS/RF, EMC, AND HIGH-SPEED ELECTRONICS Other titles in the EDN Series for Design Engineers Analog and Digital Filter Design, Second Edition, by Steve Winder 0-7506-7547-0, Paperback, 512 pgs., $59.99 Practical RF Handbook, Third Edition, by Ian Hickman 0-7506-5369-8, Paperback, 304 pgs., $39.99 Power Supply Cookbook, Second Edition, by Marty Brown 0-7506-7329-X, Paperback, 336 pgs., $39.99 Radio Frequency Transistors, Norman Dye and Helge Granberg 0-7506-7281-1, Paperback, 320 pgs., $49.99 Troubleshooting Analog Circuits, by Robert A. Pease 0-7506-9499-8, Paperback, 217 pgs., $34.99 The Art and Science of Analog Circuit Design, edited by Jim Williams 0-7506-7062-2, Paperback, 416 pgs., $34.99 Introducing the BOOKSTORE Visit the Bookstore at www.ednmag/bookstore.com ● Hundreds of great technical books by engineers for engineers ● Monthly drawings for FREE books ● Specials offers & discount pricing ● FREE sample chapters The Bookstore offers you: ELECTROMAGNETICS EXPLAINED A HANDBOOK FOR WIRELESS/RF, EMC, AND HIGH-SPEED ELECTRONICS Ron Schmitt Amsterdam Boston London Oxford New York Paris San Diego San Francisco Singapore Sydney Tokyo An imprint of Elsevier Science Newnes is an imprint of Elsevier Science. Copyright © 2002 by Elsevier Science (USA) All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or trans- mitted in any form or by any means, electronic, mechanical, photocopying, record- ing, or otherwise, without the prior written permission of the publisher. Recognizing the importance of preserving what has been written, Elsevier Science prints its books on acid-free paper whenever possible. Library of Congress Cataloging-in-Publication Data Schmitt, Ron. Electromagnetics explained: a handbook for wireless/RF, EMC, and high-speed electronics / Ron Schmitt. p. cm. Includes bibliographical references and index. ISBN 0-7506-7403-2 (hc.: alk. paper) 1. Electronics. 2. Radio. 3. Electromagnetic theory. I. Title. TK7816 .S349 2002 621.381—dc21 2001055860 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. The publisher offers special discounts on bulk orders of this book. For information, please contact: Manager of Special Sales Elsevier Science 225 Wildwood Avenue Woburn, MA 01801-2041 Tel: 781-904-2500 Fax: 781-904-2620 For information on all Elsevier Science publications available, contact our World Wide Web home page at: http://www.newnespress.com 10987654321 Printed in the United States of America CONTENTS PREFACE xi ACKNOWLEDGMENTS xv 1 INTRODUCTION AND SURVEY OF THE ELECTROMAGNETIC SPECTRUM 1 The Need for Electromagnetics 1 The Electromagnetic Spectrum 3 Electrical Length 8 The Finite Speed of Light 8 Electronics 9 Analog and Digital Signals 12 RF Techniques 12 Microwave Techniques 16 Infrared and the Electronic Speed Limit 16 Visible Light and Beyond 18 Lasers and Photonics 20 Summary 21 2 FUNDAMENTALS OF ELECTRIC FIELDS 25 The Electric Force Field 25 Other Types of Fields 26 Voltage and Potential Energy 28 Charges in Metals 30 The Definition of Resistance 32 Electrons and Holes 33 Electrostatic Induction and Capacitance 34 Insulators (Dielectrics) 38 Static Electricity and Lightning 39 The Battery Revisited 45 Electric Field Examples 47 Conductivity and Permittivity of Common Materials 47 v 3 FUNDAMENTALS OF MAGNETIC FIELDS 51 Moving Charges: Source of All Magnetic Fields 51 Magnetic Dipoles 53 Effects of the Magnetic Field 56 The Vector Magnetic Potential and Potential Momentum 68 Magnetic Materials 69 Magnetism and Quantum Physics 73 4 ELECTRODYNAMICS 75 Changing Magnetic Fields and Lenz’s Law 75 Faraday’s Law 76 Inductors 76 AC Circuits, Impedance, and Reactance 78 Relays, Doorbells, and Phone Ringers 79 Moving Magnets and Electric Guitars 80 Generators and Microphones 80 The Transformer 81 Saturation and Hysteresis 82 When to Gap Your Cores 82 Ferrites: The Friends of RF, High-Speed Digital, and Microwave Engineers 83 Maxwell’s Equations and the Displacement Current 84 Perpetual Motion 86 What About D and H? The Constituitive Relations 87 5 RADIATION 89 Storage Fields versus Radiation Fields 89 Electrical Length 91 The Field of a Static Charge 94 The Field of a Moving Charge 96 The Field of an Accelerating Charge 96 X-Ray Machines 98 The Universal Origin of Radiation 98 The Field of an Oscillating Charge 99 The Field of a Direct Current 99 The Field of an Alternating Current 102 Near and Far Field 105 The Fraunhoffer and Fresnel Zones 107 Parting Words 108 6 RELATIVITY AND QUANTUM PHYSICS 111 Relativity and Maxwell’s Equations 111 Space and Time Are Relative 115 vi CONTENTS Space and Time Become Space-Time 120 The Cosmic Speed Limit and Proper Velocity 120 Electric Field and Magnetic Field Become the Electromagnetic Field 124 The Limits of Maxwell’s Equations 125 Quantum Physics and the Birth of the Photon 126 The Quantum Vacuum and Virtual Photons 130 Explanation of the Magnetic Vector Potential 133 The Future of Electromagnetics 133 Relativity, Quantum Physics, and Beyond 134 7 THE HIDDEN SCHEMATIC 139 The Non-Ideal Resistor 139 The Non-Ideal Capacitor 142 The Non-Ideal Inductor 143 Non-Ideal Wires and Transmission Lines 146 Other Components 149 Making High-Frequency Measurements of Components 150 RF Coupling and RF Chokes 150 Component Selection Guide 151 8 TRANSMISSION LINES 153 The Circuit Model 153 Characteristic Impedance 155 The Waveguide Model 157 Relationship between the Models 159 Reflections 159 Putting It All Together 161 Digital Signals and the Effects of Rise Time 163 Analog Signals and the Effects of Frequency 165 Impedance Transforming Properties 167 Impedance Matching for Digital Systems 171 Impedance Matching for RF Systems 172 Maximum Load Power 173 Measuring Characteristic Impedance: TDRs 175 Standing Waves 177 9 WAVEGUIDES AND SHIELDS 181 Reflection of Radiation at Material Boundaries 182 The Skin Effect 183 Shielding in the Far Field 184 Near Field Shielding of Electric Fields 190 Why You Should Always Ground a Shield 190 CONTENTS vii Near Field Shielding of Magnetic Fields 191 Waveguides 194 Resonant Cavities and Schumann Resonance 204 Fiber Optics 204 Lasers and Lamps 205 10 CIRCUITS AS GUIDES FOR WAVES AND S-PARAMETERS 209 Surface Waves 210 Surface Waves on Wires 213 Coupled Surface Waves and Transmission Lines 214 Lumped Element Circuits versus Distributed Circuits 217 l/8 Transmission Lines 218 S-Parameters: A Technique for All Frequencies 219 The Vector Network Analyzer 223 11 ANTENNAS: HOW TO MAKE CIRCUITS THAT RADIATE 229 The Electric Dipole 229 The Electric Monopole 230 The Magnetic Dipole 230 Receiving Antennas and Reciprocity 231 Radiation Resistance of Dipole Antennas 231 Feeding Impedance and Antenna Matching 232 Antenna Pattern versus Electrical Length 236 Polarization 239 Effects of Ground on Dipoles 241 Wire Losses 244 Scattering by Antennas, Antenna Aperture, and Radar Cross-Section 245 Directed Antennas and the Yagi-Uda Array 246 Traveling Wave Antennas 246 Antennas in Parallel and the Folded Dipole 248 Multiturn Loop Antennas 249 12 EMC 251 Part I: Basics Self-Compatibility and Signal Integrity 251 Frequency Spectrum of Digital Signals 252 Conducted versus Induced versus Radiated Interference 255 Crosstalk 257 Part II: PCB Techniques Circuit Layout 259 PCB Transmission Lines 260 viii CONTENTS The Path of Least Impedance 262 The Fundamental Rule of Layout 264 Shielding on PCBs 265 Common Impedance: Ground Rise and Ground Bounce 267 Star Grounds for Low Frequency 269 Distributed Grounds for High Frequency: The 5/5 Rule 269 Tree or Hybrid Grounds 270 Power Supply Decoupling: Problems and Techniques 271 Power Supply Decoupling: The Design Process 278 RF Decoupling 282 Power Plane Ripples 282 90 Degree Turns and Chamfered Corners 282 Layout of Transmission Line Terminations 283 Routing of Signals: Ground Planes, Image Planes, and PCB Stackup 285 3W Rule for Preventing Crosstalk 286 Layout Miscellany 286 Layout Examples 287 Part III: Cabling Ground Loops (Multiple Return Paths) 287 Differential Mode and Common Mode Radiation 290 Cable Shielding 296 13 LENSES, DISHES, AND ANTENNA ARRAYS 307 Reflecting Dishes 307 Lenses 311 Imaging 313 Electronic Imaging and Antenna Arrays 316 Optics and Nature 319 14 DIFFRACTION 321 Diffraction and Electrical Size 321 Huygens’ Principle 323 Babinet’s Principle 324 Fraunhofer and Fresnel Diffraction 325 Radio Propagation 326 Continuous Media 327 15 FREQUENCY DEPENDENCE OF MATERIALS, THERMAL RADIATION, AND NOISE 331 Frequency Dependence of Materials 331 Heat Radiation 338 CONTENTS ix Circuit Noise 343 Conventional and Microwave Ovens 343 APPENDIX A ELECTRICAL ENGINEERING BOOK RECOMMENDATIONS 349 INDEX 353 x CONTENTS [...]... general view, this book can be utilized by anyone learning electromagnetics or RF theory, be they scientist, engineer, or technician In addition to self-study, it could serve well as a companion text for a traditional class on electromagnetics or as a companion text for classes on RF or high-speed electronics Those readers interested in RF or electromagnetics in general will find the entire book useful... many details These low-frequency approximations give us the familiar world of basic circuit theory THE NEED FOR ELECTROMAGNETICS So why would an electrical engineer need to know all this theory? There are many reasons why any and all electrical engineers need to understand electromagnetics Electromagnetics is necessary for achieving 1 2 INTRODUCTION AND SURVEY OF THE ELECTROMAGNETIC SPECTRUM electromagnetic...PREFACE This book is the result of many years of wondering about and researching the conceptual foundations of electromagnetics My goal was to write a book that provided the reader with a conceptual understanding of electromagnetics and the insight to efficiently apply this understanding to real problems that confront scientists, engineers, and technicians The fundamental... read as it was to write Ron Schmitt, emag_schmitt@yahoo.com Orono, Maine July 2001 ACKNOWLEDGMENTS First and foremost, I want to thank my wife, Kim Tripp Not only did she give me love and patient support, she also typed in the references and drew many of the figures For this, I am greatly indebted I also want to thank my family, and particularly wish to thank my mother, Marion Schmitt, who provided the... given throughout Conceptual methods for teaching the physical sciences have long been in use, but I think that the field of electromagnetics has been neglected and needs a book such as this If relativity, quantum theory, and particle physics can be taught without mathematics, why not electromagnetics? As inspiration and guide for my writing I looked to the style of writing in works such as The Art of Electronics... the electromagnetic spectrum, and also includes some other relevant information If some of these terms are unfamiliar to you, don’t fret—they’ll be explained as you progress through the book ELECTRICAL LENGTH An important concept to aid understanding of electromagnetics is electrical length Electrical length is a unitless measure that refers to the length of a wire or device at a certain frequency It... electrically short.) Circuits that are electrically short can in general be fully described by basic circuit theory without any need to understand electromagnetics On the other hand, circuits that are electrically long require RF techniques and knowledge of electromagnetics At audio frequencies and below ( . is required for any new theories or conclusions. The material that I cover has been addressed formally in the literature, and readers are encouraged to pursue the numerous references given throughout Electric Guitars 80 Generators and Microphones 80 The Transformer 81 Saturation and Hysteresis 82 When to Gap Your Cores 82 Ferrites: The Friends of RF, High-Speed Digital, and Microwave Engineers. environ- ment. In most EMC problems, the product can be categorized as either an aggressor or a victim. When a product is acting as an aggressor, it is either radiating energy or creating stray reactive