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Fields and Waves

Fields and Waves 23
Fields and Waves IThese Slides Were Prepared by Prof. Kenneth A. Connor Using Original Materials Written Mostly by the Following:  Kenneth A. Connor – ECSE Department, Rensselaer Polytechnic Institute, Troy, NY  J. Darryl Michael – GE Global Research Center, Niskayuna, NY  Thomas P. Crowley – National Institute of Standards and Technology, Boulder, CO  Sheppard J. Salon – ECSE Department, Rensselaer Polytechnic Institute, Troy, NY  Lale Ergene – ITU Informatics Institute, Istanbul, Turkey  Jeffrey Braunstein – ChungAng University, Seoul, Korea Materials from other sources are referenced where they are used. Those listed as Ulaby are figures from Ulaby’s textbook. 18 July 2017 Fields and Waves I 2Examples of Antennas 18 July 2017 Fields and Waves I 3Antennas 18 July 2017 Fields and Waves I 4moteiv Tmote Sky Inverted F Antenna 18 July 2017 Fields and Waves I 5moteiv Tmote Sky 18 July 2017 Fields and Waves I 6moteiv Tmote Sky 18 July 2017 Fields and Waves I 7moteiv Tmote Sky 18 July 2017 Fields and Waves I 8moteiv Tmote Sky 18 July 2017 Fields and Waves I 918 July 2017 Fields and Waves I 10Transmission Lines Antennas  Review Transmission Lines  Review Boundary Conditions  Review Voltage, Current, Electric and Magnetic Fields  Etc. 18 July 2017 Fields and Waves I 11TEM Waves on Transmission Lines Connecting Uniform Plane Waves with Voltages and Currents on Transmission Lines:  jz jz E (z) E eE e x  jz jz E e E e  H (z) y  18 July 2017 Fields and Waves I 12TEM Waves These fields can exist in the region between the conducting plates if the boundary conditions on the plates are reasonably satisfied. Since the electric field has only an x component, it is totally normal to the conducting boundaries. This can occur if there is a surface charge on the boundary,  jz jz E (z)E eE e s x The magnetic field is totally tangent to the conducting boundary, which can occur if there is a surface current density given by  jz jz E e E e  J H (z) s y  18 July 2017 Fields and Waves I 13TEM Waves Then, assuming that the lower plate is grounded, the voltage on the upper plate will be s  jz jz jz jz v z E (z)dx sE esE eV eV e  x  0 where we have integrated the electric field along the vertical (red) w path shown. s 18 July 2017 Fields and Waves I 14TEM Waves To connect the magnetic field with the current, we must integrate along a closed path that encloses one of the two conductors. The bottom path shown includes the horizontal (green) path inside the field region and the blue path outside of the field region. (We assume no fringing in this ideal case.) The magnetic field only contributes along the green path. Thus  jz jz w wE ewE e  i z H (z)dy  y  0   jz jz jz jz wsE ewsE e V eV e   s s w 18 July 2017 Fields and Waves I 15TEM Waves For a parallel plate waveguide (stripline), the inductance and capacitance per unit length and intrinsic impedance are w s c l s w s l s s w Z o w c w w s 18 July 2017 Fields and Waves I 16TEM Waves so the current expression is  jz jz V eV e  i(z) Z o We could have determined this current from the surface current density so we should check to be sure that the two results agree. The total current at any z should be given by  jz jz jz jz E e E e V eV e  i(z) J w w s  Z o as before. 18 July 2017 Fields and Waves I 17TEM Waves Finally, we can check to see if the charge per unit length (as determined from the boundary condition) gives us the usual capacitance per unit length. w  jz jz jz jz q wwE ewE e V eV e cv z   s s as expected. The same analysis can be done for coaxial cables and twowire lines. The general results are the same. 18 July 2017 Fields and Waves I 18Standing Waves: Voltage Standing Wave with Short Circuit Load Constructive Interference Destructive Interference 18 July 2017 Fields and Waves I 19Standing Waves: Voltage Standing Wave with Open Circuit Load 18 July 2017 Fields and Waves I 20Java Applet of Waves Standing Wave  http://www.bessernet.com/Ereflecto/tutorialFrameset.htm 18 July 2017 Fields and Waves I 21Simple Antennas  Currents on Wire Antennas  General Types of Antennas  The Hertzian Dipole as the Model Antenna  Other Simple Wire Configurations  Antenna Parameters Analysis  Radiation Patterns  Yagi Patch Antennas  Polarization 18 July 2017 Fields and Waves I 22Simple Wire Antenna Currents From CTA Johnk Engineering Electromagnetic Fields Waves 18 July 2017 Fields and Waves I 23Simple Wire Antenna Currents 18 July 2017 Fields and Waves I 24Simple Wire Antenna Currents 18 July 2017 Fields and Waves I 25Simple Wire Antenna Currents 18 July 2017 Fields and Waves I 26Simple Wire Antenna Currents 18 July 2017 Fields and Waves I 27Types of Antennas 18 July 2017 Fields and Waves I 28Constant Currents Hertzian Dipole Note the Coordinates 18 July 2017 Fields and Waves I 29Hertzian Dipole 18 July 2017 Fields and Waves I 30Note that the waves become planar at large distances 18 July 2017 Fields and Waves I 31Hertzian Dipole Radiation is primarily to the side Radiation is isotropic or uniform around the axis of the antenna Little or no radiation up or down 18 July 2017 Fields and Waves I 3218 July 2017 Fields and Waves I 3318 July 2017 Fields and Waves I 34Short Dipole 18 July 2017 Fields and Waves I 3518 July 2017 Fields and Waves I 36Aperture Antennas 18 July 2017 Fields and Waves I 37Antenna Parameters  Calculate the Electric and Magnetic Fields from the Antenna Currents – usually requires the use of potentials  Far Fields are Products of terms like the following – (depends on current and inversely on position), spherical wave, field pattern F   Determine the Poynting Vector – Power Density is product of E and H – average goes inversely with 2 position squared and with F   Gain is the ratio of power density to isotropic value  Radiation Resistance is twice the average total power divided by the current squared 18 July 2017 Fields and Waves I 38Antenna Analysis Hertzian Dipole 18 July 2017 Fields and Waves I 39Antenna Analysis 18 July 2017 Fields and Waves I 40Antenna Analysis 18 July 2017 Fields and Waves I 41Antenna Analysis  Keep Only The Largest Terms in the Far Field 18 July 2017 Fields and Waves I 42Antenna Analysis 2 F  18 July 2017 Fields and Waves I 43Antenna Analysis 18 July 2017 Fields and Waves I 44Note that the waves become planar at large distances 18 July 2017 Fields and Waves I 45Hertzian Dipole Radiation is primarily to the side Radiation is isotropic or uniform around the axis of the antenna Little or no radiation up or down 18 July 2017 Fields and Waves I 46Half Wave Dipole 2 F  18 July 2017 Fields and Waves I 47Radiation Patterns http://www.hyperlinktech.com/web/hg914y.php 18 July 2017 Fields and Waves I 4818 July 2017 Fields and Waves I 4918 July 2017 Fields and Waves I 5018 July 2017 Fields and Waves I 5118 July 2017 Fields and Waves I 5218 July 2017 Fields and Waves I 5318 July 2017 Fields and Waves I 54Antenna Patterns 18 July 2017 Fields and Waves I 55Yagi Antenna 5.8GHz 18 July 2017 Fields and Waves I 5610 Element Yagi http://www.astronwireless.com/library.html 18 July 2017 Fields and Waves I 5718 July 2017 Fields and Waves I 58Patch Antenna 18 July 2017 Fields and Waves I 59Patch Antenna 18 July 2017 Fields and Waves I 60Patch Antenna 18 July 2017 Fields and Waves I 61Patch Antenna 18 July 2017 Fields and Waves I 6218 July 2017 Fields and Waves I 6318 July 2017 Fields and Waves I 64http://etd.lib.fsu.edu/theses/available/etd04102004 143656/unrestricted/Chapter4.pdf 18 July 2017 Fields and Waves I 6518 July 2017 Fields and Waves I 6618 July 2017 Fields and Waves I 67http://journals.tubitak.gov.tr/elektrik/issues/elk05131/elk131704077.pdf 18 July 2017 Fields and Waves I 68Antenna Polarization A linear polarized antenna radiates wholly in one plane containing the direction of propagation. In a circular polarized antenna, the plane of polarization rotates in a circle making one complete revolution during one period of the wave. If the rotation is clockwise looking in the direction of propagation, the sense is called righthandcircular (RHC). If the rotation is counterclockwise, the sense is called lefthandcircular (LHC). An antenna is said to be vertically polarized (linear) when its electric field is perpendicular to the Earth's surface. An example of a vertical antenna is a broadcast tower for AM radio or the "whip" antenna on an automobile. Antenna Polarization Application Note http://www.astronwireless.com/polarization.html By Joseph H. Reisert 18 July 2017 Fields and Waves I 69Antenna Polarization Horizontally polarized (linear) antennas have their electric field parallel to the Earth's surface. Television transmissions in the USA use horizontal polarization. A circular polarized wave radiates energy in both the horizontal and vertical planes and all planes in between. The difference, if any, between the maximum and the minimum peaks as the antenna is rotated through all angles, is called the axial ratio or ellipticity and is usually specified in decibels (dB). If the axial ratio is near 0 dB, the antenna is said to be circular polarized. If the axial ratio is greater than 12 dB, the polarization is often referred to as elliptical. Antenna Polarization Application Note http://www.astronwireless.com/polarization.html By Joseph H. Reisert 18 July 2017 Fields and Waves I 70Antenna Polarization In the early days of FM radio in the 88108 MHz spectrum, the radio stations broadcasted horizontal polarization. However, in the 1960's, FM radios became popular in automobiles which used vertical polarized receiving whip antennas. As a result, the FCC modified Part 73 of the rules and regulations to allow FM stations to broadcast RHC or elliptical polarization to improve reception to vertical receiving antennas as long as the horizontal component was dominant. Antenna Polarization Application Note http://www.astronwireless.com/polarization.html By Joseph H. Reisert 18 July 2017 Fields and Waves I 71Antenna Polarization Circular polarization is most often use on satellite communications. This is particularly desired since the polarization of a linear polarized radio wave may be rotated as the signal passes through any anomalies (such as Faraday rotation) in the ionosphere. Furthermore, due to the position of the Earth with respect to the satellite, geometric differences may vary especially if the satellite appears to move with respect to the fixed Earth bound station. Circular polarization will keep the signal constant regardless of these anomalies. Antenna Polarization Application Note http://www.astronwireless.com/polarization.html By Joseph H. Reisert 18 July 2017 Fields and Waves I 72Antenna Polarization Why is a TV signal horizontally polarized Because manmade noise is predominantly vertically polarized. Do the transmitting and receiving antennas need to have the same polarization Yes. http://www.hp.com/rnd/pdfhtml/antenna.htm 18 July 2017 Fields and Waves I 73Antennas The simplest antenna is the Hertzian dipole, which looks like the following figure with the antenna axis aligned with the z direction in spherical coordinates. Transmission Line 18 July 2017 Fields and Waves I 74Antennas The electric field around the Hertzian dipole – note the vertical polarization 18 July 2017 Fields and Waves I 75Antennas Power is radiated horizontally, which is a good thing since this means that such antennas can easily communicate with one another on the surface of the earth. The range in angle is more than sufficient to handle the small elevation changes that characterize the earth’s surface. 18 July 2017 Fields and Waves I 76Antennas – Half Wave Dipole vs Quarter Wave Monopole 18 July 2017 Fields and Waves I 77Antennas – Half Wave Dipole vs Quarter Wave Monopole 18 July 2017 Fields and Waves I 78Antennas – Half Wave Dipole vs Quarter Wave Monopole 18 July 2017 Fields and Waves I 79Bertoni Slides  Extensive Slides on Propagation, Etc for Wireless http://eeweb1.poly.edu/faculty/bertoni/el675. html 18 July 2017 Fields and Waves I 80
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