Wave Propagation and Antenna Engineering

Wave Propagation and Antenna Engineering

Wave Propagation and Antenna Engineering SANJAY KUMAR Air Commodore (Retd.) Former AOC, 9 BRD, IAF Pune and Former Principal Adviser Defence Avionics Research Establishment (DARE) DRDO, Bangalore SAURABH SHUKLA Scientist Defence Avionics Research Establishment (DARE) DRDO, Bangalore Delhi-110092 2016

WAVE PROPAGATION AND ANTENNA ENGINEERING Sanjay Kumar and Saurabh Shukla 2016 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-5104-2 The export rights of this book are vested solely with the publisher. Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Mohan Makhijani at Rekha Printers Private Limited, New Delhi-110020.

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Contents Preface xvii 1. Fundamentals of Electromagnetics 1 47 1.1 Introduction 1 1.2 Spherical Coordinate System 1 1.3 Electromagnetic (EM) Spectrum 3 1.4 International Telecommunication Union (ITU) 4 1.5 Institute of Electrical and Electronics Engineers (IEEE) 5 1.6 Some Important Vector Operations 6 1.7 Time and Frequency Domain Representation 8 1.8 Maxwell s Equations 8 1.9 Helmholtz Equation or Vector Wave Equation 11 1.10 Relationship between Decibels and Nepers 12 1.11 Types of Medium 14 1.11.1 Wave Equation in Free Space 14 1.11.2 Wave Equation in Conductor (or Conducting Medium) 15 1.11.3 Wave Equation in Good Conductor (or Good Conducting Medium) 16 1.11.4 Wave Propagation in Lossless Dielectric (or Good Dielectric) 18 1.12 Skin Depth 20 1.13 Equation of Uniform Plane Wave 21 1.14 Poynting Theorem and Poynting Vector 23 1.15 Polarisation of Electromagnetic Wave 26 1.16 Reflection and Transmission of EM Waves 29 1.17 Transmission Lines 32 1.18 Smith Chart 36 Summary 42 Review Questions 44 Multiple Choice Questions 44 Numerical Problems 47 2. Wave Propagation-I: Ground and Space Wave Propagation 48 95 2.1 Introduction 48 2.2 Radio Wave Propagation 48 vii

viii Contents 2.3 Ground Wave (Surface Wave) 49 2.3.1 Application 50 2.3.2 Field Strength at Finite Distance due to Ground Waves 51 2.4 Reflection from Flat Earth 58 2.4.1 Reflection Coefficient of Horizontal Polarised Wave 60 2.4.2 Reflection Coefficient of Vertical Polarised Wave 62 2.5 Wave Tilt of Surface Wave 63 2.6 Friis Free Space Equation 65 2.7 Space Wave or Tropospheric Wave Propagation 68 2.7.1 Space Wave Field Strength 69 2.7.2 Normal Refraction 73 2.7.3 Radio Horizon: Line of Sight (LOS) for Space Waves 74 2.7.4 Equivalent Radius of Earth 78 2.8 Factors Affecting Space Wave Propagation 82 2.8.1 Effect of the Curvature of Earth s Surface 82 2.8.2 Effect of Earth s Imperfections and Roughness 83 2.8.3 Effect of Hills, Buildings and Other Obstacles 83 2.8.4 Field Strength Variation with Height 83 2.8.5 Effect of Polarisation of Space Wave 84 2.8.6 Effect of Transition between Ground Wave and Space Wave 84 2.9 Atmospheric Effects in Space Wave Propagation 85 2.9.1 Refractive Index of Air 85 2.9.2 Duct Propagation 87 2.9.3 Tropospheric Scattering 88 Summary 89 Review Questions 91 Multiple Choice Questions 92 Numerical Problems 94 3. Wave Propagation-II: Ionospheric Wave Propagation 96 138 3.1 Introduction 96 3.2 Earth s Atmosphere 96 3.2.1 Troposphere 96 3.2.2 Stratosphere 97 3.2.3 Ionosphere 97 3.3 Sky Wave or Ionospheric Wave Propagation 100 3.3.1 Refractive Index of Ionosphere 100 3.3.2 Plasma and Plasma Frequency (f p ) 102 3.3.3 Critical Frequency (f c ) 103 3.3.4 Maximum Usable Frequency (MUF) 104 3.3.5 Maximum Usable Frequency (f MUF ) for Short Distance Communication 106 3.3.6 Maximum Usable Frequency (f MUF ) for Long Distance Communication 107

Contents ix 3.3.7 Optimum Working Frequency (OWF) 113 3.3.8 Lowest Usable Frequency (LUF) 114 3.3.9 Skip Distance 115 3.3.10 Skip Zone (Dead Zone) 117 3.3.11 Actual and Virtual Height 117 3.4 Fading 119 3.4.1 Multipath Fading 120 3.4.2 Selective Fading 120 3.4.3 Interference Fading 120 3.4.4 Absorption Fading 121 3.4.5 Polarisation Fading 121 3.4.6 Skip Fading 121 3.5 Diversity Schemes 121 3.5.1 Time Diversity 122 3.5.2 Frequency Diversity 122 3.5.3 Space Diversity 122 3.5.4 Polarisation Diversity 122 3.6 Transmission Losses 122 3.7 Effect of Earth s Magnetic Field 123 3.7.1 Expression for Gyrofrequency 124 3.7.2 Magneto-Ionic Theory 125 3.7.3 Magneto-Ionic Splitting 126 3.8 Faraday Rotation 127 3.9 Variations in the Ionosphere 129 3.9.1 Regular Variations 130 3.9.2 Irregular Variations 131 3.10 Energy Losses Due to Collisions in Ionosphere 132 Summary 133 Review Questions 134 Multiple Choice Questions 135 Numerical Problems 137 4. Antenna Fundamentals 139 203 4.1 Introduction 139 4.2 Isotropic Radiator 139 4.3 Average Power from an Isotropic Antenna 141 4.4 Radiation Mechanism 141 4.5 Types of Antenna 145 4.6 Fundamental Antenna Parameters 146 4.6.1 Antenna Input Impedance 147 4.6.2 Antenna VSWR and Return Loss 149 4.6.3 Antenna Bandwidth 151 4.6.4 Radiation Pattern 152 4.6.5 Antenna Radiation Lobes 155

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