RADIOWAVE PROPAGATION Physics and Applications CURT A. LEVIS JOEL T. JOHNSON FERNANDO L. TEIXEIRA The cover illustration is part of a figure from R.C. Kirby, "Introduction," Lecture 1 in NBS Course in Radio Propagation, Ionospheric Propagation, Central Radio Propagation Laboratory, National Bureau of Standards, U.S. Department of Commerce, Boulder, CO 1961. See Figure 1.5 for the original. WILEY A JOHN WILEY & SONS, INC., PUBLICATION
CONTENTS Preface xi 1 Introduction 1 1.1 Definition of Propagation, 1 1.2 Propagation and Systems Design, 2 1.3 Historical Perspective, 3 1.4 The Influence of Signal Frequency and Environment, 4 1.5 Propagation Mechanisms, 6 1.6 Summary, 12 1.7 Sources of Further Information, 14 1.8 Overview of Text, 15 2 Characterization of Propagation Media 17 2.1 Introduction, 17 2.2 Maxwell's Equations, Boundary Conditions, and Continuity, 17 2.3 Constitutive Relations, 19 2.4 Dielectric Behavior of Materials: Material Polarization, 20 2.5 Material Properties, 21 2.5.1 Simple Media, 22 2.6 Magnetic and Conductive Behavior of Materials, 30 2.6.1 Equivalence of Ohmic and Polarization Losses, 30 References, 34 v
vi CONTENTS 3 Plane Waves 36 3.1 Introduction, 36 3.2 D'Alembert's Solution, 37 3.3 Pure Traveling Waves, 39 3.4 Information Transmission, 41 3.5 Sinusoidal Time Dependence in an Ideal Medium, 42 3.6 Plane Waves in Lossy and Dispersive Media, 46 3.7 Phase and Group Velocity, 49 3.8 Wave Polarization, 52 References, 55 4 Antenna and Noise Concepts 56 4.1 Introduction, 56 4.2 Antenna Concepts, 56 4.3 Basic Parameters of Antennas, 57 4.3.1 Receiving Antennas, 62 4.4 Noise Considerations, 66 4.4.1 Internal Noise, 66 4.4.2 External Noise, 68 References, 75 5 Direct Transmission 76 5.1 Introduction, 76 5.2 Friis Transmission Formula, 77 5.2.1 Including Losses in the Friis Formula, 78 5.3 Atmospheric Gas Attenuation Effects, 80 5.3.1 Total Attenuation on Horizontal or Vertical Atmospheric Paths, 82 5.3.2 Total Attenuation on Slant Atmospheric Paths, 83 5.3.3 Attenuation at Higher Frequencies and Further Information Sources, 84 5.4 Rain Attenuation, 85 5.4.1 Describing Rain, 87 5.4.2 Computing Rain Specific Attenuation, 89 5.4.3 A Simplified Form for Rain Specific Attenuation, 90 5.4.4 Computing the Total Path Attenuation Through Rain, 92 5.4.5 Attenuation Statistics, 96 5.4.6 Frequency Scaling, 97
5.4.7 Rain Margin Calculations: An Example, 98 5.4.8 Site Diversity Improvements, 99 5.5 Scintillations, 102 Appendix 5.A Look Angles to Geostationary Satellites, 103 References, 105 Reflection and Refraction 6.1 Introduction, 106 6.2 Reflection from a Planar Interface: Normal Incidence, 106 6.3 Reflection from a Planar Interface: Oblique Incidence, 108 6.3.1 Plane of Incidence, 109 6.3.2 Perpendicular Polarized Fields in Regions 1 and 2, 110 6.3.3 Phase Matching and Snell's Law, 111 6.3.4 Perpendicular Reflection Coefficient, 113 6.3.5 Parallel Polarized Fields in Regions 1 and 2, 113 6.3.6 Parallel Reflection Coefficient, 115 6.3.7 Summary of Reflection Problem, 115 6.4 Total Reflection and Critical Angle, 118 6.5 Refraction in a Stratified Medium, 120 6.6 Refraction Over a Spherical Earth, 121 6.7 Refraction in the Earth's Atmosphere, 127 6.8 Ducting, 129 6.9 Ray-Tracing Methods, 132 References, 134 Terrain Reflection and Diffraction 7.1 Introduction, 135 7.2 Propagation Over a Plane Earth, 136 7.2.1 Field Received Along Path Ri: The Direct Ray, 137 7.2.2 Field Received Along Path R 2 : The Reflected Ray, 138 7.2.3 Total Field, 138 7.2.4 Height-Gain Curves, 140 7.3 Fresnel Zones, 141 7.3.1 Propagation Over a Plane Earth Revisited in Terms of Fresnel Zones, 144 7.4 Earth Curvature and Path Profile Construction, 145 7.5 Microwave Link Design, 147 7.5.1 Distance to the Radio Horizon, 149
7.5.2 Height-Gain Curves in the Obstructed Region, 151 7.5.3 Height-Gain Curves in the Reflection Region, 154 7.6 Path Loss Analysis Examples, 154 7.7 Numerical Methods for Path Loss Analysis, 158 7.8 Conclusion, 160 References, 160 Empirical Path Loss and Fading Models 8.1 Introduction, 161 8.2 Empirical Path Loss Models, 162 8.2.1 Review of the Flat Earth Direct plus Reflected Model, 163 8.2.2 Empirical Model Forms, 164 8.2.3 Okumura-Hata Model, 164 8.2.4 COST-231/Hata Model, 166 8.2.5 Lee Model, 167 8.2.6 Site-General ITU Indoor Model, 168 8.2.7 Other Models for Complex Terrain, 168 8.2.8 An Example of Empirical Path Loss Model Usage, 168 8.3 Signal Fading, 170 8.3.1 A Brief Review of Probability Theory, 172 8.3.2 Statistical Characterization of Slow Fading, 174 8.3.3 Statistical Characterization of Narrowband Fast Fading, 176 8.3.4 Example Fading Analyses, 183 8.4 Narrowband Fading Mitigation Using Diversity Schemes, 184 8.5 Wideband Channels, 185 8.5.1 Coherence Bandwidth and Delay Spread, 185 8.5.2 Coherence Time and Doppler Spread, 186 8.6 Conclusion, 187 References, 187 Groundwave Propagation 9.1 Introduction, 189 9.2 Planar Earth Groundwave Prediction, 190 9.2.1 Elevated Antennas: Planar Earth Theory, 194 9.3 Spherical Earth Groundwave Prediction, 196 9.4 Methods for Approximate Calculations, 199 9.5 A 1 MHz Sample Calculation, 200 9.6 A 10 MHz Sample Calculation, 203
9.7 ITU Information and Other Resources, 204 9.8 Summary, 205 Appendix 9.A Spherical Earth Groundwave Computations, 211 References, 213 Characteristics of the Ionosphere 10.1 Introduction, 214 10.2 The Barometric Law, 215 10.3 Chapman's Theory, 218 10.3.1 Introduction, 218 10.3.2 Mathematical Derivation, 219 10.4 Structure of the Ionosphere, 226 10.5 Variability of the Ionosphere, 229 References, 233 Ionospheric Propagation 11.1 Introduction, 235 11.2 Dielectric Properties of an Ionized Medium, 237 11.3 Propagation in a Magnetoionic Medium, 240 11.3.1 Mathematical Derivation of the Appleton-Hartree Equation, 241 11.3.2 Physical Interpretation, 247 11.3.3 Ordinary and Extraordinary Waves, 247 11.3.4 The ÖL and ß T Approximations, 248 11.4 Ionospheric Propagation Characteristics, 249 11.5 Ionospheric Sounding, 250 11.5.1 Ionograms, 251 11.5.2 Examples of Actual Ionograms, 254 11.6 The Secant Law, 257 11.7 Transmission Curves, 258 11.8 Breit and Tuve's Theorem, 260 11.9 Martyn's Theorem on Equivalent Virtual Heights, 261 11.10 MUF, "Skip" Distance, and Ionospheric Signal Dispersion, 262 11.11 Earth Curvature Effects and Ray-Tracing Techniques, 266 11.12 Ionospheric Propagation Prediction Tools, 267 11.13 Ionospheric Absorption, 268 11.14 Ionospheric Effects on Earth-Space Links, 270 11.14.1 Faraday Rotation, 271 11.14.2 Group Delay and Dispersion, 273
X CONTENTS 11.14.3 Ionospheric Scintillations, 275 11.14.4 Attenuation, 277 11.14.5 Ionospheric Refraction, 278 11.14.6 Monitoring TEC Distribution, 278 References, 280 12 Other Propagation Mechanisms and Applications 282 12.1 Introduction, 282 12.2 Tropospheric Scatter, 282 12.2.1 Introduction, 282 12.2.2 Empirical Model for the Median Path Loss, 285 12.2.3 Fading in Troposcatter Links, 285 12.3 Meteor Scatter, 286 12.4 Tropospheric Delay in Global Satellite Navigation Systems, 288 12.5 Propagation Effects on Radar Systems, 291 References, 293 Index 295