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Syllabus Electromagnetic Theory
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Syllabus for Electromagnetic Theory
Elements of vector calculus: divergence and curl; Gauss and Stoke’s theorems, Maxwell’s
equations: differential and integral forms. Wave equation, Poynting vector. Plane waves:
propagation through various media; reflection and refraction; phase and group velocity; skin
depth. Transmission lines: characteristic impedance; impedance transformation; Smith chart;
impedance matching; S parameters, pulse excitation. Waveguides: modes in rectangular
waveguides; boundary conditions; cut-off frequencies; dispersion relations. Basics of
propagation in dielectric waveguide and optical fibers. Basics of Antennas: Dipole antennas;
radiation pattern; antenna gain.
Analysis of GATE Papers
(Electromagnetic Theory)
Year Percentage of marks Overall Percentage
2013 5.00
9.12%
2012 12.00
2011 9.00
2010 7.00
2009 8.00
2008 8.00
2007 10.67
2006 12.00
2005 8.71
2004 9.34
2003 10.67
Contents Electromagnetic Theory
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CC OO NN TT EE NN TT SS
Chapter Page No
#1. Electromagnetic Field 1 – 49 Introduction to Vector Calculus 1 – 7
Material and Physical Constants 7 – 8
Electromagnetic (EM Field) 8 – 18
Divergence of Current Density and Relaxation 18 – 22
The Magnetic Vector Potential 22 – 27
Faraday Law 27 – 29
Maxwell’s Equation’s 29 – 36
Assignment 1 37 – 39
Assignment 2 40 – 42
Answer keys 43
Exlanations 43 – 49
#2. EM Wave Propagation 50 – 86 Introduction 50
General wave equations 50 – 51
Plane wave in a Dielectric medium 51 – 53
Poynting Vector 53 – 54
Phase Velocity 55 – 64
Wave Polarization 64 -71
Assignment 1 72 – 74
Assignment 2 74 – 78
Answer keys 79
Exlanations 79 – 86
#3. Transmission Lines 87 – 127 Introduction 87 – 98
Transmission & Reflection of Waves on a Transmission Line 98 – 100
Impedance of a Transmission Line 100 – 106
The Smith Chart 107 – 108
Scattering Parameters 108 – 109
Strip Line 109 – 113
Assignment 1 114 – 116
Assignment 2 116 – 119
Answer keys 120
Exlanations 120 – 127
#4. Guided E.M Waves 128 – 161 Wave Guide 128 – 130
Transverse Magnetic Mode 130 – 133
Transverse Electric Mode 133 – 142
Circuter Wave Guide 142 – 152
Contents Electromagnetic Theory
THE GATE ACADEMY PVT.LTD. H.O.: #74, Keshava Krupa (third Floor), 30th Cross, 10th Main, Jayanagar 4th Block, Bangalore-11 : 080-65700750, [email protected] © Copyright reserved. Web: www.thegateacademy.com Page II
Assignment 1 153 – 155
Assignment 2 155 – 156
Answer keys 157
Exlanations 157 – 161
#5. Antennas 162 – 199 Inroduction 162
Hertzian Dipole 162 – 165
Field Regions 165
Radiation Pattern 165 – 166
Radiaton Intensity 166 – 168
Antenna Radiation Efficiency 168 – 170
Antenna Arrays 170 – 175
Solved Examples 176 – 188
Assignment 1 189 – 191
Assignment 2 191 – 193
Answer keys 194
Exlanations 194 – 199
Module Test 200 – 215 Test Questions 200 – 207
Answer Keys 208
Explanations 208 – 215
Reference Books 216
Chapter 1 Electromagnetic Theory
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CHAPTER 1
Electromagnetic Field
Introduction to vector calculus
Cartesian coordinates (x, y, z), x , y , z Cylindrical coordinates ( , , z), , , z Spherical coordinates (r, , ) , r , , Vector calculus formula
Table 1.1 S. No Cartesian coordinates Cylindrical
coordinates Spherical coordinates
(a) Differential displacement dl = dx + dy + dz
dl = d + d
+dz
dl = dr + rd + r sin d
(b) Differential area ds = dydz = dxdz
= dxdy
ds = d dz
= d dz = d d
ds = r sin d d = r sin dr d = r dr d
(c) Differential volume dv = dxdydz
dv = d d dz dv = r sin d d dr
Operators
1) V – gradient , of a Scalar V
2) .V – divergence , of a vector V
3) V – curl , of a vector V 4) V – laplacian , of a scalar V
DEL Operator
=
(Cartesian)
=
(Cylindrical)
=
(Spherical)
Gradient of a Scalar field V is a vector that represents both the magnitude and the direction of maximum space rate of increase of V.
V =
=
=
Chapter 1 Electromagnetic Theory
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The following are the fundamental properties of the gradient of a scalar field V:
1. The m gnitude of V equ ls the m ximum r te of ch nge in V per unit dist nce. 2. V points in the direction of the maximum rate of change in V. 3. V t ny point is perpendicular to the constant V surface that passes through that point. 4. If A = V, V is s id to be the sc l r potenti l of A. 5. The projection of V in the direction of unit vector |a| is V. |a| and is called the directional
derivative of V along |a|. This is the rate of change of V in direction of |a|.
Example: Find the gradient of the following scalar fields:
(a) V = e sin 2x cosh y (b) U = z cos (c) W = r sin cos
Solution
(a) V =
= e cos x cosh y e sin x sinh y e sin x cosh y
(b) U =
= z cos z sin cos
(c) W =
= sin cos sin cos sin
Divergence of vector
A at a given point P is the outward flux per unit volume as the volume shrinks about P.
Hence,
divA = . A = lim ∮ .
(1)
Where, V is the volume enclosed by the closed surf ce S in which P is loc ted. Physic lly, we
may regard the divergence of the vector field A⃗⃗ at a given point as a measure of how much the field diverges or emanates from that point.
.A =
=
( A )
=
(r A )
(A sin )
From equation (1), ∮ A ds
= ∫ . A dv
Chapter 1 Electromagnetic Theory
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This is called divergence theorem which states that the total outward flux of the vector field A through a closed surface S is same as the volume integral of the divergence of A. Example
Determine the divergence of these vector field:
(a) P = x yz xz (b) Q = sin z z cos
(c) T =
cos r sin cos cos
Solution
(a) P =
P
P
P
=
x(x yz)
y( )
z(xz)
= xyz x
(b) Q =
( Q )
Q
Q
=
( sin )
( z)
z (z cos )
= sin cos
(c) T =
(r T )
(T sin )
(T )
=
r
r(cos )
r sin
(r sin cos )
r sin
(cos )
=
r sin r sin cos cos
= cos cos
Curl of a vector field provides the maximum value of the circulation of the field per unit area and indicates the direction along which this maximum value occurs.
That is,
curl A = A = lim (∮ .
)
------------- (2)
A = |
A A A
|
=
|
A A A
|
Chapter 1 Electromagnetic Theory
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=
|
r r sin
A rA r sin A
|
From equation (2) we may expect that ∮ . = ∫ (
).
This is called stoke’s theorem, which states that the circulation of a vector field A around a (closed) path L is equal to the surface integral of the curl of A over the open surface S bounded by L. Example Determine the curl of each of the vector fields of previous Example. Solution
(a) = (
) (
) (
)
= ( ) ( ) ( )
= ( )
(b) = *
+ *
+
*
( )
+
= (
) ( )
( )
=
( ) ( )
(c) =
*
( )
+
*
( )+
*
( )
+
=
[
( )
( )]
[
( )
( )]
[
( )
( )
]
=
( )
( )
(
)
= (
)
(
)
(a) Laplacian of a scalar field V, is the divergence of the gradient of V and is written as .
=
=
(
)
=
(
)
(
)
If = 0, V is said to be harmonic in the region. A vector field is solenoid if .A = ; it is irrot tion l or conserv tive if A =
. ( ) = ( ) =
Chapter 1 Electromagnetic Theory
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(b) Laplacian of vector A̅
A⃗⃗ = is lw ys vector qu ntity
A⃗⃗ = ( A ) ̂x ( A ) ̂y ( A ) ̂z
A Sc l r qu ntity A Sc l r qu ntity
A Sc l r qu ntity
V =
........Poission’s Eqn
V = ........Laplace Eqn
E = ⃗⃗
E
....... wave Eqn
Example
The potential (scalar) distribution is given as
V = y x if E0 : permittivity of free space what is the change density p at the point (2,0)?
Solution
Poission’s Eqn V =
(
) ( y x ) =
x x x x x y =
At pt( , ) x x x =
=
Example
Find the Laplacian of the following scalar fields,
(a) V = e sin 2x cosh y (b) U = z cos (c) W = r sin cos
Solution
The Laplacian in the Cartesian system can be found by taking the first derivative and later the second derivative.
(a) V =
=
x( e cos x coshy)
y(e sin x sinh y)
z( e sin x cosh y)
= e sin x cosh y e sin x coshy e sin x cosh y = e sin x cosh y
(b) U =
(
)
Chapter 1 Electromagnetic Theory
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=
( z cos )
z cos
= z cos z cos =
(c) W =
(r
)
(sin
)
=
r
r( r sin cos )
r sin
( r sin sin cos )
r sin cos
r sin
= sin cos
r
r cos sin cos
r sin
r sin cos cos
r sin
cos
r
= cos
r ( sin cos cos )
= cos
r( cos )
Stoke’s theorem
Statement:- closed line integral of any vector A⃗⃗ integrated over any closed curve C is always
equal to the surface integral of curl of vector A⃗⃗ integr ted over the surf ce re ‘s’ which is enclosed by the closed curve ‘c’
∮ A⃗⃗ . d ⃗ = ∫ ∫( x A⃗⃗ ) dS⃗
The theorem is valid irrespective of
(i) Shape of closed curve ‘C’ (ii) Type of vector ‘A’ (iii) Type of co-ordinate system. Divergence theorem
∯ A⃗⃗
dS⃗ = ∭ V⃗⃗ . A⃗⃗ dv
S
V
S
C