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RS 1 ENE 428 Microwave Engineering Lecture 1 Introduction, Maxwell’s equations, fields in media, and boundary conditions

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RS 2 Syllabus Assoc. Prof. Dr. Rardchawadee Silapunt (Ann), Dr. Ekapon Siwapornsathain (Eric), Tel: Lecture: 9:00am-12:00pm Wednesday, AIT Instructors at King Mongkut’s University of Technology Thonburi, BKK, Thailand Textbook: Microwave Engineering by David M. Pozar (3 rd edition Wiley, 2005) Recommended additional textbook: Applied Electromagnetics by Stuart M.Wentworth (2 nd edition Wiley, 2007)

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4 Homework 10% Quiz 10% Midterm exam 40% Final exam 40% Grading Vision Providing opportunities for intellectual growth in the context of an engineering discipline for the attainment of professional competence, and for the development of a sense of the social context of technology.

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10-11/06/51 RS 5 Course overview Maxwell’s equations and boundary conditions for electromagnetic fields Uniform plane wave propagation Transmission lines Matching networks Waveguides Two-port networks Resonators Antennas Microwave communication systems

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RS 6 Microwave frequency range (300 MHz – 300 GHz) ( = 1 mm – 1 m in free space) Microwave components are distributed components. Lumped circuit elements approximations are invalid. Maxwell’s equations are used to explain circuit behaviors ( and ) Introduction

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RS 7 Lumped circuit model and distributed circuit model

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RS 8 From Maxwell’s equations, if the electric field is changing with time, then the magnetic field varies spatially in a direction normal to its orientation direction Knowledge of fields in media and boundary conditions allows useful applications of material properties to microwave components A uniform plane wave, both electric and magnetic fields lie in the transverse plane, the plane whose normal is the direction of propagation Introduction (2)

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RS 11 Point forms of Maxwell’s equations (1) (2) (3) (4)

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RS 13 The magnetic north can never be isolated from the south. Magnetic field lines always form closed loops.

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RS 14 Maxwell’s equations in free space = 0, r = 1, r = 1 0 = 4 x10 -7 Henrys/m 0 = 8.854x Farads/m = conductivity (1/ohm) (“constitutive parameters”) Ampère’s law Faraday’s law

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RS 15 Integral forms of Maxwell’s equations Note: To convert from the point forms to the integral forms, we need to apply Stoke’s Theorem (for (1) and (2)) and Divergence theorem (for (3) and (4)), respectively. (1) (2) (3) (4)

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RS 16 Fields are assumed to be sinusoidal or harmonic, and time dependence with steady-state conditions Time dependence form: Phasor form:

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RS 17 Maxwell’s equations in phasor form (1) (2) (3) (4)

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RS 18 Fields in dielectric media (1) An applied electric field causes the polarization of the atoms or molecules of the material to create electric dipole moments that complements the total displacement flux, where is the electric polarization. In the linear medium, it can be shown that Then we can write

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RS 19 Fields in dielectric media (2) may be complex then can be complex and can be expressed as Imaginary part is counted for loss in the medium due to damping of the vibrating dipole moments. The loss of dielectric material may be considered as an equivalent conductor loss if the material has a conductivity . Loss tangent is defined as

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RS 20 Anisotropic dielectrics The most general linear relation of anisotropic dielectrics can be expressed in the form of a tensor which can be written in matrix form as

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RS 21 Analogous situations for magnetic media (1) An applied magnetic field causes the magnetic polarization of by aligned magnetic dipole moments where is the magnetic polarization or magnetization. In the linear medium, it can be shown that Then we can write

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RS 22 Analogous situations for magnetic media (2) may be complex then can be complex and can be expressed as Imaginary part is counted for loss in the medium due to damping of the vibrating dipole moments.

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RS 23 Anisotropic magnetic material The most general linear relation of anisotropic material can be expressed in the form of a tensor which can be written in matrix form as

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RS 24 Boundary conditions between two media H t1 H t2 E t2 E t1 B n2 B n1 D n2 D n1

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RS 25 Fields at a dielectric interface Boundary conditions at an interface between two lossless dielectric materials with no charge or current densities can be shown as

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RS 26 Fields at the interface with a perfect conductor Boundary conditions at the interface between a dielectric with the perfect conductor can be shown as

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RS 27 General plane wave equations (1) Consider medium free of charge For linear, isotropic, homogeneous, and time- invariant medium, assuming no free magnetic current, (1) (2)

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RS 28 General plane wave equations (2) Take curl of (2), we yield From then For charge free medium

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RS 29 Helmholtz wave equation For electric field For magnetic field

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RS 30 Time-harmonic wave equations Transformation from time to frequency domain Therefore

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RS 31 Time-harmonic wave equations or where This term is called propagation constant or we can write = + j where = attenuation constant (Np/m) = phase constant (rad/m)

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RS 32 Solutions of Helmholtz equations Assuming the electric field is in x-direction and the wave is propagating in z- direction The instantaneous form of the solutions Consider only the forward-propagating wave, we have Use Maxwell’s equation, we get

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RS 33 Solutions of Helmholtz equations in phasor form Showing the forward-propagating fields without time- harmonic terms. Conversion between instantaneous and phasor form Instantaneous field = Re(e j t phasor field)

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RS 34 Intrinsic impedance For any medium, For free space

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RS 35 Propagating fields relation where represents a direction of propagation

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