Antennas And Wave Propagation - WordPress
Antennas andWavePropagationBy: Harish, A.R.; Sachidananda, M.Oxford University Press
2007 Oxford University PressISBN: 978‐0‐19‐568666‐1
PrefaceAntennas are a key component of all types of wireless communication—beit the television sets in our homes, the FM radios in our automobiles, or themobile phones which have become an almost integral part of most people’sdaily lives. All these devices require an antenna to function. In fact, it wasan antenna which led Arno Penzias and Robert Wilson to their Nobel Prizewinning discovery of cosmic background radiation.The study of antennas and their field patterns is an important aspectof understanding many applications of wireless transmission technology.Antennas vary widely in their shapes, sizes, and radiation characteristics.Depending on the usage requirements, an antenna can be a single piece ofwire, a huge reflective disc, or a complex array of electrical and electroniccomponents. The analysis of antennas is almost invariably concomitantwith the study of the basic concepts of the propagation of electromagneticwaves through various propagation media and the discontinuities encountered in the path of propagation.About the BookEvolved from the lecture notes of courses taught by the authors at theIndian Institute of Technology Kanpur over several years, Antennas andWave Propagation is primarily meant to fulfil the requirements of asingle-semester undergraduate course on antennas and propagation theory.It is assumed that the reader has already gone through a basic courseon electromagnetics and is familiar with Maxwell’s equations, plane waves,reflection and refraction phenomena, transmission lines, and waveguides.The book provides a lucid overview of electromagnetic theory and a comprehensive introduction to various types of antennas and their radiationcharacteristics. Further, a clear-cut presentation of the basic concepts ofv
viPrefacewave propagation, including ground wave and ionospheric propagation, goeson to make this text a useful and self-contained reference on antennas andradio wave propagation.While a rigorous analysis of an antenna is highly mathematical, oftena simplified analysis is sufficient for understanding the basic principles ofoperation of an antenna. Keeping this fact in mind, this book emphasizesthe conceptual understanding of the principles of radiation and wave propagation by keeping the mathematical analysis to a minimum.In most cases, the design of an antenna is system specific. Simplifieddesign procedures, rather than a rigorous mathematical analysis, are usefuland practical for designing and building antennas for many communicationapplications. Hence, several simple antenna design procedures have beenincluded, which give an engineering flavour to the book.Content and StructureThis book contains eight chapters which provide a comprehensive treatmentof antennas and wave propagation.Chapter 1 is essentially a review of basic electromagnetic theory. It alsointroduces the vector potential approach to the solution of the wave equationand the concept of the Hertzian dipole.In Chapter 2, students are introduced to the terminology used for describing the radiation and input characteristics of antennas. The terms used forcharacterizing an antenna as a receiver are also clearly explained. The calculation of free space communication link budget is illustrated with examples.The development of antenna theory starts from a study of the radiation from an infinitesimal current element. In Chapter 3, the field computation is extended to antennas carrying linear current distributions, e.g., shortdipole, half-wave dipole, monopole, and loop antennas. Detailed proceduresfor the computation of the performance parameters of these antennas arealso given.A class of antennas which can be looked at as radiation from an apertureis treated in Chapter 4. Various forms of the field equivalence principle andits applications in the computation of the radiation fields of an aperture areexplained. Several aperture type antennas, such as a slot, an open-endedwaveguide, horn, reflector, etc., are also discussed.Chapter 5 is devoted to the study of antenna arrays. It starts with thepattern multiplication principle and goes on to explain various pattern properties using a two-element array as an example. Use of polynomial representation of the array factor of a uniformly-spaced linear array and its pole-zero
Prefaceviirepresentation on a circle diagram is explained. The chapter ends with a discussion on the design of binomial and Chebyshev patterns.A large number of specially designed antennas exist for specific usagerequirements. Chapter 6 details a select set of such antennas under thetitle Special Antennas. These antennas cover a wide range of applicationsin various frequency bands. Some of the antennas discussed are monopole,V antenna, Yagi–Uda array, turnstile antenna, helix, spiral, microstrippatch, etc. The radiation pattern properties and some simple designprocedures are explained.Chapter 7 is focused on the techniques used to measure antenna parameters. Indoor and outdoor measurement ranges which provide free-space-likeconditions for the antenna are explained. Schematic block diagrams of themeasurement instrumentation are presented. Procedures for the measurement of the gain, directivity, radiation pattern, etc. are also discussed.Finally, Chapter 8 deals with the issues related to the propagation ofradio waves. In this chapter, we study the interaction of the media and thediscontinuities with electromagnetic waves. The effect of the earth and thetroposphere on the propagation of electromagnetic waves is considered indetail. This is followed by an exposition of the nature of the ionosphere andits effect on sky wave propagation.Each chapter is divided into sections that are independent. A large numberof solved problems are interspersed through the text to enable the studentto comprehensively grasp concepts and their applications. Suitable figuresand diagrams have been provided for easy understanding of the conceptsinvolved. Relevant numerical problems with answers have been included asend-chapter exercises to test the understanding of the topics introduced ineach chapter. Seven different appendices provide easy reference to importantformulae that are used throughout the book. These are followed by a listof references for those interested in further reading. A special attempt hasbeen made to include topics that are part of curricula of courses offered bya large cross-section of educational institutes.AcknowledgementsIt is a pleasure to thank our wives Radha and Shalini, and children Bhavanaand Bharath for their love, care, and emotional support. We are gratefulto them for enduring the countless hours of absence during the preparation of the manuscript. We appreciate the advice and support from friendsand colleagues, which helped us in the preparation of the manuscript. Wewould like to thank IIT Kanpur, and especially the Department of Electrical
viiiPrefaceEngineering, IIT Kanpur, for providing a conducive environment for writing the book. We are grateful to the Centre for Development of TechnicalEducation, IIT Kanpur, for the financial support. Prof. R. Nityananda,Centre Director, NCRA, TIFR, Pune, has been kind enough to permit us touse a photograph of the GMRT facility. We would like to thank him for hiskind gesture. The editorial team at Oxford University Press India has donea commendable job in bringing out this book. We would like to expressour gratitude for the excellent editing, graphics, and design of the book.Teaching the antenna theory course has given us an opportunity to interactwith many students, which has helped in improving the presentation of thematerial. We thank all the students who have interacted with us.Although much care has been taken to ensure an error-free text, someerrors may have crept in. Feedback from the readers regarding such errorswill be highly appreciated and will go a long way in helping us improve thesubsequent editions.A.R. HarishM. Sachidananda
ContentsPrefaceSymbolsCHAPTER 1 Electromagnetic RadiationIntroduction1.1 Review of Electromagnetic Theory1.1.1 Vector Potential Approachxv11491.1.2 Solution of the Wave Equation111.1.3 Solution Procedure181.2 Hertzian DipoleExercisesCHAPTER 2 Antenna Characteristics193031Introduction312.1 Radiation Pattern322.2 Beam Solid Angle, Directivity, and Gain442.3 Input Impedance492.4 Polarization532.4.1 Linear Polarization542.4.2 Circular Polarization562.4.3 Elliptical Polarization582.5 Bandwidth59ix
xContents2.6 Receiving Antenna602.6.1 Reciprocity602.6.2 Equivalence of Radiation and Receive Patterns662.6.3 Equivalence of Impedances672.6.4 Effective Aperture682.6.5 Vector Effective Length732.6.6 Antenna Temperature802.7 Wireless Systems and Friis Transmission FormulaExercisesCHAPTER 3 Wire Antennas859094Introduction943.1 Short Dipole943.1.1 Radiation Resistance and Directivity1033.2 Half-wave Dipole1063.3 Monopole1153.4 Small Loop Antenna117ExercisesCHAPTER 4 Aperture AntennasIntroduction1271291294.1 Magnetic Current and its Fields1304.2 Some Theorems and Principles1334.2.1 Uniqueness Theorem1344.2.2 Field Equivalence Principle1344.2.3 Duality Principle1364.2.4 Method of Images1374.3 Sheet Current Distribution in Free Space4.3.1 Pattern Properties1391434.3.2 Radiation Pattern as a Fourier Transform of the CurrentDistribution1494.4 Expressions for a General Current Distribution1544.5 Aperture in a Conducting Screen1554.6 Slot Antenna158
Contentsxi4.7 Open-ended Waveguide Radiator1594.8 Horn Antenna1604.9 Pyramidal Horn Antenna1624.10 Reflector Antenna1654.10.1 Flat-plate Reflector1674.10.2 Corner Reflector1724.10.3 Common Curved Reflector Shapes174Exercises193CHAPTER 5 Antenna ArraysIntroduction1951955.1 Linear Array and Pattern Multiplication1965.2 Two-element Array1995.3 Uniform Array2125.3.1 Polynomial Representation5.4 Array with Non-uniform Excitation2202275.4.1 Binomial Array2285.4.2 Chebyshev Array Synthesis232Exercises240CHAPTER 6 Special AntennasIntroduction6.1 Monopole and Dipole Antennas2422422436.1.1 Monopole for MF and HF Applications2436.1.2 Monopole at VHF2476.1.3 Antenna for Wireless Local Area Network Application2476.2 Long Wire, V, and Rhombic Antennas6.2.1 V Antenna2512556.3 Yagi–Uda array2626.4 Turnstile Antenna2706.4.1 Batwing and Super-turnstile Antennas6.5 Helical Antenna2732776.5.1 Axial Mode Helix2786.5.2 Normal Mode Helix282
xiiContents6.6 Biconical Antenna2836.7 Log-periodic Dipole Array2856.7.1 Design Procedure2906.8 Spiral Antenna2956.9 Microstrip Patch Antenna298ExercisesCHAPTER 7 Antenna MeasurementsIntroduction3023033037.1 Antenna Measurement Range3047.2 Radiation Pattern Measurement3147.2.1 Antenna Positioner3157.2.2 Receiver Instrumentation3187.3 Gain and Directivity3197.3.1 Absolute Gain Measurement3207.3.2 Gain Transfer Method3237.3.3 Directivity3247.4 Polarization3247.5 Input Impedance and Input Reflection Coefficient328ExercisesCHAPTER 8 Radio Wave PropagationIntroduction8.1 Ground Wave Propagation3293303303328.1.1 Free Space Propagation3338.1.2 Ground Reflection3348.1.3 Surface Waves3398.1.4 Diffraction3418.1.5 Wave Propagation in Complex Environments3448.1.6 Tropospheric Propagation3488.1.7 Tropospheric Scatter3608.2 Ionospheric Propagation3648.2.1 Electrical Properties of the Ionosphere3678.2.2 Effect of Earth’s Magnetic Field378Exercises380
ContentsxiiiAppendix A Trigonometric Formulae383Appendix B Integration Formulae385Appendix C Series Expansions387Appendix D Vector Identities389Appendix E Coordinate Systems and VectorDifferential Operators390Appendix F Coordinate Transformations393Appendix G Thesin xxFunction395References397Index399
CHAPTER 1Electromagnetic RadiationIntroductionMost of us are familiar with cellular phones. In cellular communicationsystems, there is a two-way wireless transmission between the cellular phonehandset and the base station tower. The cell phone converts the audio signals into electrical form using a microphone. This information is imposed ona high frequency carrier signal by the process of modulation. The modulatedcarrier is radiated into free space as an electromagnetic wave which is pickedup by the base station tower. Similarly, the signals transmitted by the towerare received by the handset, thus establishing a two way communication.This is one of the typical examples of a wireless communication systemwhich uses free space as a medium to transfer information from the transmitter to the receiver. A key component of a wireless link is the antennawhich efficiently couples electromagnetic energy from the transmitter tofree space and from free space to the receiver. An antenna is generally abidirectional device, i.e., the power through the antenna can flow in both thedirections, hence it works as a transmitting as well as a receiving antenna.Transmission lines are used to transfer electromagnetic energy from onepoint to another within a circuit and this mode of energy transfer is generallyknown as guided wave propagation. An antenna acts as an interface betweenthe radiated electromagnetic waves and the guided waves. It can be thoughtof as a mode transformer which transforms a guided-wave field distributioninto a radiated-wave field distribution. Since the wave impedances of theguided and the radiated waves may be different, the antenna can also bethought of as an impedance transformer. A proper design of this part isnecessary for the efficient coupling of the energy from the circuit to the freespace and vice versa.One of the important properties of an antenna is its ability to transmitpower in a preferred direction. The angular distribution of the transmitted1
2Chapter 1 Electromagnetic RadiationFig. 1.1 Parabolic dish antenna at the Department of Electrical Engineering,Indian Institute of Technology, Kanpur, India (Courtesy: Dept of EE, IIT Kanpur)power around the antenna is generally known as the radiation pattern (Amore precise definition is given in Chapter 2). For example, a cellular phoneneeds to communicate with a tower which could be in any direction, hencethe cellular phone antenna needs to radiate equally in all directions. Similarly, the tower antenna also needs to communicate with cellular phoneslocated all around it, hence its radiation also needs to be independent of thedirection.There are large varieties of communication applications where the directional property is used to an advantage. For example, in point-to-point communication between two towers it is sufficient to radiate (or receive) only inthe direction of the other tower. In such cases a highly directional parabolicdish antenna can be used. A 6.3 m diameter parabolic dish antenna used forcommunication with a geo-stationary satellite is shown in Fig. 1.1. This antenna radiates energy in a very narrow beam pointing towards the satellite.Radio astronomy is another area where highly directional antennas areused. In radio astronomy the antenna is used for receiving the electromagnetic radiations from outer space. The power density of these signals fromouter space is very low, hence it is necessary to collect the energy over a verylarge area for it to be useful for scientific studies. Therefore, radio astronomy antennas are large in size. In order to increase the collecting aperture,
Introduction3Fig. 1.2 A panoramic view of the Giant Metrewave Radio Telescope (GMRT), Pune, India, consisting of 30 fully-steerableparabolic dish antennas of 45 m diameter each spread over distances up to 25 km.1 (Photograph by Mr. Pravin Raybole, Courtesy: GMRT, Pune, http://www.gmrt.ncra.tifr.res.in)the Giant Metrewave Radio Telescope (GMRT) near Pune in India, has anarray of large dish antennas, as shown in Fig. 1.2.The ability of an antenna to concentrate power in a narrow beam dependson the size of the antenna in terms of wavelength. Electromagnetic waves ofwavelengths ranging from a few millimetres to several kilometres are usedin various applications requiring efficient antennas working at these wavelengths. These frequencies, ranging from hundreds of giga hertz to a fewkilo hertz, form the radio wave spectrum. Figure 1.3 depicts the radio wavespectrum along with band designations and typical applications.The radiation pattern of an antenna is usually computed assuming thesurroundings to be infinite free space in which the power density (powerper unit area) decays as inverse square of the distance from the antenna.In practical situations the environment is more complex and the decay isnot as simple. If the environment consists of well defined, finite number ofscatterers, we can use theories of reflection, refraction, diffraction, etc., topredict the propagation of electromagnetic waves. However, in a complexenvironment, such as a cell phone operating in an urban area, the fieldstrength is obtained by empirical relations.The atmosphere plays a significant role in the propagation of electromagnetic waves. The density of the air molecules and, hence, the refractive indexof the atmosphere changes with height. An electromagnetic wave passingthrough media having different refractive indices undergoes refraction.Thus, the path traced by an electromagnetic wave as it propagates through1The GMRT was built and is operated by the National Centre for Radio Astrophysics (NCRA)of the Tata Institute of Fundamental Research (TIFR).
4Chapter 1 Electromagnetic RadiationWavelength (m) 10310 3100Radio waves10 610 9UltravioletInfrared10 12Gamma raysX raysVisible lightRadio wave bandsBanddesignationVLFLFMFHFVerylow frequencyLowfrequencyMediumfrequencyHighfrequency Navigation Radio beaconApplicationsFrequency: 3 kHz–30 kHzWavelength: 100 km to 10 km30 kHz–300 kHz10 km to 1 kmVHF AM broadcast Shortwave Television Direction findingbroadcast FM broadcast Maritime Air traffic control Amateur radiocommunication Aircraftcommunication Amateur radio Radio astronomy300 kHz–3 MHz1 km to 100 m3 MHz–30 MHz100 m to 10 mUHFSHFVeryUltraSuperhigh frequency high frequency high frequency Television Satellitecommunication Radar Navigation Cellular telephone30 MHz–300 MHz 300 MHz–3 GHz1 m to 10 cm10 m to 1 mEHFExtremelyhigh frequency Radar Radar Microwave link Experimental studies Satellitecommunication Mobilecommunication3 GHz–30 GHz10 cm to 1 cm30 GHz–300 GHz1 cm to 1 mmMicrowave bandsBanddesignationLS1 GHz 2 GHz2 GHz 4 GHzCXKuKKa4 GHz 8 GHz 8 GHz 12.4 GHz 12.4 GHz 18 GHz 18 GHz 27 GHz 27 GHz 40 GHzMillimeter wave40 GHz 300 GHzFig. 1.3 Radio wave spectrum along with the band designations and typical applications.the atmosphere is not a straight line. The air molecules also get ionizedby solar radiation and cosmic rays. The layer of ionized particles in theatmosphere, known as the ionosphere, reflects high frequency (3 MHz to30 MHz) waves. A multi-hop communication link is established by repeatedreflections of the electromagnetic waves between the ionosphere and thesurface of the earth. This is the mode of propagation of shortwave radiosignals over several thousand kilometres.Both the radiation properties of the antennas and the propagation conditions play a very important role in establishing a successful communicationlink. This book addresses both these issues in some detail. It is assumed thatthe students have some basic knowledge of electromagnetic theory. However,in the following section some of the basic concepts of electromagnetic theoryused in the analysis of antennas are presented for easy reference as well asfor introducing the notation used in the book.1.1 Review of Electromagnetic TheoryElectromagnetic fields are produced by time-varying charge distributionswhich can be supported by time-varying current distributions. Consider sinusoidally varying electromagnetic sources. (Sources having arbitrary variation
1.1 Review of Electromagnetic Theory5with respect to time can be represented in terms of sinusoidally varyingfunctions using Fourier analysis.) A sinusoidally varyi
wave propagation, including ground wave and ionospheric propagation, goes on to make this text a useful and self-contained reference on antennas and radio wave propagation. While a rigorous analysis of an antenna is highly mathematical, often a simplified analysis is sufficient for understanding the basic principles of operation of an antenna.
Antennas and Wave Proapagation - Harish and Sachidananda: Oxford Press 2007. REFERENCE BOOKS: 1. Antenna Theory Analysis and Design - C A Balanis, 2nd ED, John Wiley, 1997 2. Antennas and Propagation for Wireless Communication Systems - Sineon R Saunders, John Wiley, 2003. 3. Antennas and wave propagation - G S N Raju: Pearson Education 2005
Antennas can be classified according to their radiation characteristics as follows: (1) omni-directional antennas, (2) pencil-beam antennas, (3) fanned-beam antennas, and (4) shaped-beam antennas. The first type of antenra will be discussed in detail in this article. The physical limitations of pencil-beam antennas will
Antenna and Transmission Line Fundamentals. 18. Flexible. Lesson 3 Ouarter-Wave, Half-Wave Antennas and. Associated Radiation Patterns 25 Flexible. Lesson 4. Long-Wire Antennas and Antenna Propagation 38 Flexible. Lesson 5 Radio Wave Propagation. 20 Flexible Student Lesson Book. 19, Supplemontary Materials Required: None. cern' WI VOCAIIPW MOM .
Ground Wave Propagation Follows contour of the earth Can Propagate considerable distances Frequencies up to 2 MHz Example oAM radio. Sky Wave Propagation. Sky Wave Propagation Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and
Contents Introduction to the Fourth Edition ix 1 Introduction to Radio Broadcasting and Communications 1 2 Radio-wave Propagation 5 3 Transmission Lines 59 4 The Smith Chart 95 5 Fundamentals of Radio Antennas 123 6 High-Frequency Dipole and Other Doublet Antennas 141 7 Vertically Polarized HF Antennas 173 8 Multiband and Tunable-Wire Antennas 203 9 Longwire Directional Antennas 213
Ground Wave Ground wave propagation occurs at low frequencies. Typically 4 MHz and below. In ground wave propagation, the magnetic field ofIn ground wave propagation, the magnetic field of the RF signal couples with the earth. A vertically polarized antenna works well for this type of propagation.
Ground-Wave Propagation Ground-wave propagation involves the transmission of a radio signal along or near the surface of the earth. The ground-wave signal is divided into three parts: the direct wave, the reflected wave, and the surface wave. The direct wave travels through the atmosphere from one
Anatomy Fig 1. Upper limb venous anatomy [1] Vessel Selection Right arm preferable to left (as the catheter is more likely to advance into the correct vessel), vessel selection in order: 1. Basilic 2. Brachial 3. Cephalic Pre-procedure Patient information and consent Purpose of procedure, risks, benefits, alternatives. Line care: Consider using local patient information leaflet as available .
