L1PropertiesofElectromagneticWaves3 - 7CEEM110: Antennas...

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1 7CEEM110 7CEEM110 : Antennas and Propagation : Antennas and Propagation Lecture 1: Properties of Electromagnetic Waves Vivien Xiaoli Chu Department of Electronic Engineering
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2 Main Topics of Antennas Main Topics of Antennas Electromagnetic (EM) fields Maxwell’s equations Govern the propagation behavior of EM waves The understanding is essential for developing an appreciation of antenna technologies. Plane waves Polarisation Hertzian dipoles Linear dipoles Antenna types Antenna arrays
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3 EM Field EM Field Energy is conveyed by EM fields. The wire in a circuit acts as a guide. EM fields surround the wires. With an alternating current, an amount of energy (usually negligible) is radiated into the space. At high frequencies a significant amount can be radiated. Computer screens and TV sets emit radiations that can be picked up at distances of a kilometer.
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4 Elementary EM Elementary EM Electromagnetics deals with the study of electrical and magnetic fields. The concept of field Electrical ( E ) and magnetic ( H ) fields are vector quantities governed by Maxwell’s equations. Scalar and vector fields Static and time-varying fields The 2 coupled vectors E and H (with 6 variables) vary with time and space.
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5 Field Field A field is associated with a region in space. A field exists if there is a physical phenomenon associated with points in that region. e.g., gravitational field The field concept provides a description of how the quantities vary with time from one point to another, e.g., Temperature field T ( x, y, z, t ) in London Velocity field v ( x, y, z, t ) of the flow in River Thames
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6 Scalars and Vectors Scalars and Vectors Scalars: quantities characterized by magnitude only. e.g., temperature, charge Represented by symbols in lightface type Vectors: quantities characterized not only by magnitude, but also a direction. e.g., velocity, acceleration, force Represented by symbols in boldface type or with an arrow above Need a set of reference directions, which are mutually orthogonal A unit vector has a magnitude unity ˆˆˆ x yz A AA  Axy z A or A
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7 Vector Analysis Vector Analysis Addition, subtraction, multiplication by a scalar Dot product Cross product Defined as a third vector C , with magnitude | C | = | A || B |sin Normal to the plane containing A and B with direction in a right- hand sense z z y y x x B A B A B A cos | || | B A B A B A A B ˆˆˆ ˆˆ () ˆ xyz yz zy zx xz xy yx AAA BBB AB    z B A B A a normal The unit vector normal to two vectors
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8 Coordinate Systems Coordinate Systems Rectangular coordinates ( x , y , z ) Differential vector Differential surface Differential volume Cylindrical coordinates Spherical coordinates 12 dd d  Sl l x y z dl 222 ˆˆˆ x d y dz dl dx dy dz   lx y z dv dxdydz
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9 Cylindrical Cylindrical C C oordinates
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This note was uploaded on 10/24/2009 for the course COMMUNICAT 74EE24E taught by Professor Imran during the Spring '09 term at Indian Institute Of Management, Kolkata.

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L1PropertiesofElectromagneticWaves3 - 7CEEM110: Antennas...

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