Introduction to Rf Propagation

INTRODUCTION TO RF PROPAGATION

John S. Seybold, Ph.D.

JOHN WILEY & SONS, INC.

INTRODUCTION TO RF PROPAGATION

John S. Seybold, Ph.D.

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

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Library of Congress Cataloging-in-Publication Data: Seybold, John S., 1958– Introduction to RF propagation / by John S. Seybold. p. cm. Includes bibliographical references and index. ISBN-13 978-0-471-65596-1 (cloth) ISBN-10 0-471-65596-1 (cloth) 1. Radio wave propagation—Textbooks. 2. Radio wave propagation—Mathematical models—Textbooks. 3. Antennas (Electronics)—Textbooks. I. Title. QC676.7.T7S49 2005 621.384¢11—dc22 2005041617

Printed in the United States of America

10987654321 To: My mother, Joan Philippe Molitor and my father, Lawrence Don Seybold

CONTENTS

Preface xiii

1. Introduction 1 1.1 Frequency Designations 1 1.2 Modes of Propagation 3 1.2.1 Line-of-Sight Propagation and the Radio Horizon 3 1.2.2 Non-LOS Propagation 5 1.2.2.1 Indirect or Obstructed Propagation 6 1.2.2.2 Tropospheric Propagation 6 1.2.2.3 Ionospheric Propagation 6 1.2.3 Propagation Effects as a Function of Frequency 9 1.3 Why Model Propagation? 10 1.4 Model Selection and Application 11 1.4.1 Model Sources 11 1.5 Summary 12 References 12 Exercises 13

2. Electromagnetics and RF Propagation 14 2.1 Introduction 14 2.2 The Electric Field 14 2.2.1 Permittivity 15 2.2.2 Conductivity 17 2.3 The Magnetic Field 18 2.4 Electromagnetic Waves 20 2.4.1 Electromagnetic Waves in a Perfect Dielectric 22 2.4.2 Electromagnetic Waves in a Lossy Dielectric or Conductor 22 2.4.3 Electromagnetic Waves in a Conductor 22 2.5 Wave Polarization 24 2.6 Propagation of Electromagnetic Waves at Material Boundaries 25 2.6.1 Dielectric to Dielectric Boundary 26 vii viii CONTENTS

2.6.2 Dielectric-to-Perfect Conductor Boundaries 31 2.6.3 Dielectric-to-Lossy Dielectric Boundary 31 2.7 Propagation Impairment 32 2.8 Ground Effects on Circular Polarization 33 2.9 Summary 35 References 36 Exercises 36

3. Antenna Fundamentals 38 3.1 Introduction 38 3.2 Antenna Parameters 38 3.2.1 Gain 39 3.2.2 Effective Area 39 3.2.3 Radiation Pattern 42 3.2.4 Polarization 44 3.2.5 Impedance and VSWR 44 3.3 Antenna Radiation Regions 45 3.4 Some Common Antennas 48 3.4.1 The Dipole 48 3.4.2 Beam Antennas 50 3.4.3 Horn Antennas 52 3.4.4 Reﬂector Antennas 52 3.4.5 Phased Arrays 54 3.4.6 Other Antennas 54 3.5 Antenna Polarization 55 3.5.1 Cross-Polarization Discrimination 57 3.5.2 Polarization Loss Factor 58 3.6 Antenna Pointing loss 62 3.7 Summary 63 References 64 Exercises 65

4. Communication Systems and the Link Budget 66 4.1 Introduction 66 4.2 Path Loss 67 4.3 Noise 69 4.4 Interference 76 4.5 Detailed Link Budget 79 4.5.1 EIRP 80 4.5.2 Path Loss 80 4.5.3 Receiver Gain 82 4.5.4 Link Margin 83 4.5.5 Signal-to-Noise Ratio 83 CONTENTS ix

4.6 Summary 84 References 85 Exercises 85

5. Radar Systems 87 5.1 Introduction 87 5.2 The Radar Range Equation 88 5.3 Radar Measurements 93 5.3.1 Range Measurement 93 5.3.2 Doppler Measurement 95 5.3.3 Angle Measurement 95 5.3.4 Signature Measurement 98 5.4 Clutter 99 5.4.1 Area Clutter 99 5.4.2 Volume Clutter 105 5.4.3 Clutter Statistics 106 5.5 Atmospheric Impairments 106 5.6 Summary 107 References 108 Exercises 109

6. Atmospheric Effects 111 6.1 Introduction 111 6.2 Atmospheric Refraction 112 6.2.1 The Radio Horizon 112 6.2.2 Equivalent Earth Radius 113 6.2.3 Ducting 116 6.2.4 Atmospheric Multipath 117 6.3 Atmospheric Attenuation 121 6.4 Loss From Moisture and Precipitation 125 6.4.1 Fog and Clouds 126 6.4.2 Snow and Dust 130 6.5 Summary 131 References 132 Exercises 132

7. Near-Earth Propagation Models 134 7.1 Introduction 134 7.2 Foliage Models 134 7.2.1 Weissberger’s Model 135 7.2.2 Early ITU Vegetation Model 135 7.2.3 Updated ITU Vegetation Model 137 x CONTENTS

7.2.3.1 Terrestrial Path with One Terminal in Woodland 138 7.2.3.2 Single Vegetative Obstruction 138 7.3 Terrain Modeling 141 7.3.1 Egli Model 141 7.3.2 Longley–Rice Model 143 7.3.3 ITU Model 144 7.4 Propagation in Built-Up Areas 146 7.4.1 Young Model 146 7.4.2 Okumura Model 146 7.4.3 Hata Model 151 7.4.4 COST 231 Model 152 7.4.5 Lee Model 153 7.4.6 Comparison of Propagation Models for Built-Up Areas 157 7.5 Summary 159 References 160 Exercises 161

8. Fading and Multipath Characterization 163 8.1 Introduction 163 8.2 Ground-Bounce Multipath 164 8.2.1 Surface Roughness 174 8.2.2 Fresnel Zones 175 8.2.3 Diffraction and Huygen’s Principle 179 8.2.4 Quantifying Diffraction Loss 179 8.3 Large-Scale or Log-Normal Fading 186 8.4 Small-Scale Fading 193 8.4.1 Delay Spread 194 8.4.2 Doppler Spread 198 8.4.3 Channel Modeling 199 8.4.4 The Probabilistic Nature of Small-Scale Fading 200 8.5 Summary 203 References 205 Exercises 206

9. Indoor Propagation Modeling 208 9.1 Introduction 208 9.2 Interference 208 9.3 The Indoor Environment 209 9.3.1 Indoor Propagation Effects 209 9.3.2 Indoor Propagation Modeling 210 CONTENTS xi

9.3.3 The ITU Indoor Path Loss Model 210 9.3.4 The Log-Distance Path Loss Model 214 9.4 Summary 216 References 216 Exercises 216

10. Rain Attenuation of Microwave and Millimeter Wave Signals 218 10.1 Introduction 218 10.2 Link Budget 219 10.3 Rain Fades 222 10.3.1 Speciﬁc Attenuation Due to Rainfall 222 10.3.2 The ITU Model 224 10.3.3 The Crane Global Model 229 10.3.4 Other Rain Models 234 10.3.5 Rain Attenuation Model Comparison 234 10.3.6 Slant Paths 234 10.4 The Link Distance Chart 234 10.5 Availability Curves 237 10.6 Other Precipitation 237 10.7 Cross-Polarization Effects 239 10.8 Summary 239 References 240 Exercises 241 Appendix 10A: Data for Rain Attenuation Models 242

11. Satellite Communications 246 11.1 Introduction 246 11.2 Satellite Orbits 247 11.3 Satellite Operating Frequency 249 11.4 Satellite Path Free-Space Loss 249 11.5 Atmospheric Attenuation 252 11.6 Ionospheric Effects 255 11.7 Rain Fades 255 11.7.1 ITU Rain Attenuation Model for Satellite Paths 257 11.7.2 Crane Rain Attenuation Model for Satellite Paths 264 11.7.3 The DAH Rain Attenuation Model 270 11.8 Antenna Considerations 273 11.9 Noise Temperature 274 11.9.1 The Hot-Pad Formula 276 11.9.2 Noise Due to Rain 278 11.9.3 Sun Outages 279 11.10 Summary 279 xii CONTENTS

References 280 Exercises 281

12. RF Safety 283 12.1 Introduction 283 12.2 Biological Effects of RF Exposure 285 12.3 CC Guidelines 287 12.4 Antenna Considerations 290 12.5 FCC Computations 292 12.5.1 Main Beam and Omnidirectional Antenna Analysis 292 12.5.2 Antenna Directivity 293 12.6 Station Evaluations 297 12.7 Summary 298 References 298 Exercises 299

Appendix A: Review of Probability for Propagation Modeling 301

Index 317 PREFACE

With the rapid expansion of wireless consumer products, there has been a con- siderable increase in the need for radio-frequency (RF) planning, link planning, and propagation modeling. A network designer with no RF background may find himself/herself designing a wireless network. A wide array of RF planning software packages can provide some support, but there is no substi- tute for a fundamental understanding of the propagation process and the lim- itations of the models employed. Blind use of computer-aided design (CAD) programs with no understanding of the physical fundamentals underlying the process can be a recipe for disaster. Having witnessed the results of this approach, I hope to spare others this frustration. A recent trend in electrical engineering programs is to push RF, network, and communication system design into the undergraduate electrical engineering curriculum. While important for preparing new graduates for industry, it can be particularly challenging, because most undergraduates do not have the breadth of background needed for a thorough treatment of each of these subjects. It is hoped that this text will provide sufficient background for students in these areas so that they can claim an understanding of the fundamentals as well as being conversant in relevant modeling techniques. In addi- tion, I hope that the explanations herein will whet the student’s appetite for further study in the many facets of wireless communications. This book was written with the intent of serving as a text for a senior-level or first-year graduate course in RF propagation for electrical engineers. I believe that it is also suitable as both a tutorial and a reference for practicing engineers as well as other competent technical professionals with a need for an enhanced understanding of wireless systems. This book grew out of a graduate course in RF propagation that I developed in 2001. The detailed explanations and examples should make it well-suited as a textbook. While there are many excellent texts on RF propagation, many of them are specifically geared to cellular telephone systems and thus restrictive in their scope. The applications of wireless range far beyond the mobile telecommunications industry, however, and for that reason I believe that there is a need for a com- prehensive text. At the other end of the spectrum are the specialized books that delve into the physics of the various phenomena and the nuances of various modeling techniques. Such works are of little help to the uninitiated reader requiring a practical understanding or the student who is encountering RF propagation for the first time. The purpose of this text is to serve as a first xiii