Seybold J.S. Introduction to RF Propagation
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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
viii CONTENTS
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
CONTENTS ix
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
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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
CONTENTS xi
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
xii CONTENTS
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 plan-
ning, 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 engi-
neering curriculum. While important for preparing new graduates for indus-
try, 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 funda-
mentals 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 grad-
uate course in RF propagation that I developed in 2001. The detailed expla-
nations 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
introduction to RF propagation and the associated modeling. It has been
written from the perspective of a seasoned radar systems engineer who sees
RF propagation as one of the key elements in system design rather than an
end in itself. No attempt has been made to cover all of the theoretical aspects
of RF propagation or to provide a comprehensive survey of the available
models. Instead my goal is to provide the reader with a basic understanding
of the concepts involved in the propagation of electromagnetic waves and
exposure to some of the commonly used modeling techniques.
There are a variety of different phenomena that govern the propagation of
electromagnetic waves. This text does not provide a detailed analysis of all of
the physics involved in each of these phenomena, but should provide a solid
understanding of the fundamentals, along with proven modeling techniques.
In those cases where the physics is readily apparent or relative to the actual
formulation of the model, it is presented. The overall intent of this text is to
serve as a first course in RF propagation and provide adequate references for
the interested reader to delve into areas of particular relevance to his/her
needs.
The field of RF propagation modeling is extremely diverse and has many
facets, both technical and philosophical. The models presented herein are
those that I perceive as the most commonly used and/or widely accepted.They
are not necessarily universally accepted and may not be the best choice for a
particular application. Ultimately, the decision as to which model to use rests
with the system analyst. Hopefully the reader will find that this book provi-
des sufficient understanding to make the required judgments for most
applications.
ACKNOWLEDGMENTS
The most difficult aspect of this project has been declaring it finished. It seems
that each reading of the manuscript reveals opportunities for editorial
improvement, addition of more material, or refinement in the technical pre-
sentation. This is an inevitable part of writing. Every effort has been made to
correct any typographical or technical errors in this volume. Inevitably some
will be missed, for which I apologize. I hope that this book is found sufficiently
useful to warrant multiple printings and possibly a second edition.To that end,
I would appreciate hearing from any readers who uncover errors in the man-
uscript, or who may have suggestions for additional topics.
I have had the privilege of working with many fine engineers in my career,
some of whom graciously volunteered to review the various chapters of this
book prior to publication. I want to thank my friends and colleagues who
reviewed portions of the manuscript, particularly Jerry Brand and Jon
McNeilly, each of whom reviewed large parts of the book and made many
valuable suggestions for improvement. In addition, Harry Barksdale, Phil
DiPiazza, Francis Parsche, Parveen Wahid, John Roach III, and Robert Heise
xiv PREFACE
PREFACE xv
each reviewed one or more chapters and lent their expertise to improving
those chapters.
I also want to thank my publisher, who has been extremely patient in
walking me through the process and who graciously provided me with two
deadline extensions, the second of which to accommodate the impact of our
back-to-back hurricanes on the east coast of Florida.
Finally, I want to thank my wife Susan and our children Victoria and Nathan,
who had to share me on many weekends and evenings as this project pro-
gressed. I am deeply indebted to them for their patience and understanding.
The Mathcad files used to generate some of the book’s figures can be found
at ftp://ftp.wiley.com/public/sci_tech_med/rf_propagation. These files include
the ITU atmospheric attenuation model, polarization loss factor as a function
of axial ratio, and some common foliage attenuation models.
J
OHN S. SEYBOLD
1
Introduction to RF Propagation, by John S. Seybold
Copyright © 2005 by John Wiley & Sons, Inc.
CHAPTER 1
Introduction
As wireless systems become more ubiquitous, an understanding of radio-
frequency (RF) propagation for the purpose of RF planning becomes increas-
ingly important. Most wireless systems must propagate signals through
nonideal environments. Thus it is valuable to be able to provide meaningful
characterization of the environmental effects on the signal propagation. Since
such environments typically include far too many unknown variables for a
deterministic analysis, it is often necessary to use statistical methods for
modeling the channel. Such models include computation of a mean or median
path loss and then a probabilistic model of the additional attenuation that is
likely to occur.What is meant by “likely to occur” varies based on application,
and in many instances an availability figure is actually specified.
While the basics of free-space propagation are consistent for all frequen-
cies, the nuances of real-world channels often show considerable sensitivity to
frequency. The concerns and models for propagation will therefore be heavily
dependent upon the frequency in question. For the purpose of this text, RF is
any electromagnetic wave with a frequency between 1MHz and 300 GHz.
Common industry definitions have RF ranging from 1 MHz to about 1 GHz,
while the range from 1 to about 30 GHz is called microwaves and 30–
300 GHz is the millimeter-wave (MMW) region. This book covers the HF
through EHF bands, so a more appropriate title might have been Introduc-
tion to Electromagnetic Wave Propagation, but it was felt that the current title
would best convey the content to the majority of potential readers.
1.1 FREQUENCY DESIGNATIONS
The electromagnetic spectrum is loosely divided into regions as shown in Table
1.1 [1]. During World War II, letters were used to designate various frequency
bands, particularly those used for radar. These designations were classified at
the time, but have found their way into mainstream use. The band identifiers
may be used to refer to a nominal frequency range or specific frequency ranges