The document discusses the main principles of radiation from antennas. It begins by explaining that antennas are usually made of metal and function by creating differences in potential that control charge distribution and generate electromagnetic fields. Radiation occurs when charges encounter discontinuities like bends that change their speed. Resonant structures like dipole antennas produce continuous radiation through oscillating charges. The document then examines the electric and magnetic fields produced by elementary sources like Hertzian dipoles and how these far fields propagate in free space according to Maxwell's equations.
This document provides preparatory notes and examples for an exam on electromagnetic theory. It covers key concepts like the Lorentz force equation, Biot-Savart law, Ampere's circuital law, Gauss's law for magnetism, and magnetic boundary conditions. Examples calculate the magnetic field and force on charges in various configurations like an infinite line current, parallel wires, and a ring of current. The document is a useful study guide summarizing the essential electromagnetic concepts and formulas tested on the exam.
The document discusses sources of magnetic fields, including the Biot-Savart law which describes the magnetic field from a current-carrying wire. It provides an example of calculating the magnetic field from a long straight wire using the Biot-Savart law. It also discusses the magnetic force between two parallel current-carrying wires and the magnetic field from a circular current loop. Ampere's law relates the line integral of the magnetic field around a closed loop to the current passing through the loop. The document concludes by discussing magnetic materials and their effect on applied magnetic fields.
1. The document describes an experiment to measure the charge-to-mass ratio of electrons using Thomson's cathode ray tube.
2. Two methods are used: 1) null deflection where electric and magnetic fields cancel each other out, and 2) deflection by a magnetic field alone where the radius of curvature is measured.
3. Equations are derived relating the experimental measurements to the charge-to-mass ratio. The results from both methods are within 2% of the accepted value, validating Thomson's original discovery of the electron.
The document describes a lab experiment to measure the Hall effect using an Indium Arsenide sample. Students will apply a magnetic field perpendicular to the current flow and measure the resulting Hall voltage. This will allow them to determine properties like the Hall coefficient, carrier mobility, and doping density. Additionally, the Hall device can be used as a magnetic field sensor by measuring the Hall voltage produced by varying currents through an electromagnet.
The document discusses Maxwell's equations and electromagnetism, providing an overview of Maxwell's equations which describe the relationship between electric and magnetic fields, motion of charged particles in electromagnetic fields, electromagnetic wave propagation, and basic vector calculus equations. It also lists several textbooks for further reading on classical electromagnetism and provides the basic Maxwell's equations in vacuum and source forms.
The document discusses Maxwell's equations and electromagnetism, providing an overview of Maxwell's equations which describe the relationship between electric and magnetic fields, motion of charged particles in electromagnetic fields, electromagnetic wave propagation, and basic vector calculus equations. It also lists several textbooks for further reading on classical electromagnetism and provides the source-free and source Maxwell's equations in vacuum.
1) James Clerk Maxwell unified existing laws of electricity and magnetism through his equations, revealing that changing electric and magnetic fields propagate as electromagnetic waves traveling at the speed of light.
2) Solving Maxwell's equations results in the wave equation, showing that light is an electromagnetic wave.
3) Electromagnetic waves carry energy through space, and all remote sensing is based on the modulation of this energy.
This document provides preparatory notes and examples for an exam on electromagnetic theory. It covers key concepts like the Lorentz force equation, Biot-Savart law, Ampere's circuital law, Gauss's law for magnetism, and magnetic boundary conditions. Examples calculate the magnetic field and force on charges in various configurations like an infinite line current, parallel wires, and a ring of current. The document is a useful study guide summarizing the essential electromagnetic concepts and formulas tested on the exam.
The document discusses sources of magnetic fields, including the Biot-Savart law which describes the magnetic field from a current-carrying wire. It provides an example of calculating the magnetic field from a long straight wire using the Biot-Savart law. It also discusses the magnetic force between two parallel current-carrying wires and the magnetic field from a circular current loop. Ampere's law relates the line integral of the magnetic field around a closed loop to the current passing through the loop. The document concludes by discussing magnetic materials and their effect on applied magnetic fields.
1. The document describes an experiment to measure the charge-to-mass ratio of electrons using Thomson's cathode ray tube.
2. Two methods are used: 1) null deflection where electric and magnetic fields cancel each other out, and 2) deflection by a magnetic field alone where the radius of curvature is measured.
3. Equations are derived relating the experimental measurements to the charge-to-mass ratio. The results from both methods are within 2% of the accepted value, validating Thomson's original discovery of the electron.
The document describes a lab experiment to measure the Hall effect using an Indium Arsenide sample. Students will apply a magnetic field perpendicular to the current flow and measure the resulting Hall voltage. This will allow them to determine properties like the Hall coefficient, carrier mobility, and doping density. Additionally, the Hall device can be used as a magnetic field sensor by measuring the Hall voltage produced by varying currents through an electromagnet.
The document discusses Maxwell's equations and electromagnetism, providing an overview of Maxwell's equations which describe the relationship between electric and magnetic fields, motion of charged particles in electromagnetic fields, electromagnetic wave propagation, and basic vector calculus equations. It also lists several textbooks for further reading on classical electromagnetism and provides the basic Maxwell's equations in vacuum and source forms.
The document discusses Maxwell's equations and electromagnetism, providing an overview of Maxwell's equations which describe the relationship between electric and magnetic fields, motion of charged particles in electromagnetic fields, electromagnetic wave propagation, and basic vector calculus equations. It also lists several textbooks for further reading on classical electromagnetism and provides the source-free and source Maxwell's equations in vacuum.
1) James Clerk Maxwell unified existing laws of electricity and magnetism through his equations, revealing that changing electric and magnetic fields propagate as electromagnetic waves traveling at the speed of light.
2) Solving Maxwell's equations results in the wave equation, showing that light is an electromagnetic wave.
3) Electromagnetic waves carry energy through space, and all remote sensing is based on the modulation of this energy.
1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
The document discusses several topics related to magnetic effects of electric currents:
1. Lorentz force law describes the force experienced by a moving charge in a magnetic field. Fleming's left hand rule indicates the direction of this force.
2. Instruments like galvanometers, ammeters, and voltmeters make use of the magnetic force on a current-carrying coil. Galvanometers can be adapted into ammeters using a shunt resistor or voltmeters using a series resistor.
3. Other topics covered include the magnetic field due to parallel currents, torque on a current-carrying coil, cyclotron particle acceleration, and the maximum energy attainable by particles in a cyclotron.
This document discusses circuit and network theory. It covers topics such as circuit elements and laws, magnetic circuits, network analysis, network theorems, AC circuits and resonance, coupled circuits, transients, two-port networks, and filters. Mesh analysis is introduced as a technique for network analysis that is applicable to planar networks containing voltage sources. The key steps are selecting mesh currents, then writing and solving KVL equations in terms of the unknown currents.
Cbse class 12 physics sample paper 02 (for 2014)mycbseguide
The document provides a sample physics question paper for Class 12 with 29 questions ranging from 1 to 5 marks. It includes questions from various topics in physics like electromagnetism, optics, modern physics, semiconductor devices, communication systems, and electrical circuits. The paper tests concepts, calculations, principles, diagrams, and applications of concepts across different areas of the physics syllabus. It provides guidelines for time, marks distribution and instructions for answering the questions.
This document discusses electromagnetic waves and applications of Faraday's laws of induction. It begins by outlining the learning objectives which include Faraday's laws, induced EMF directions and magnitudes, and practical applications. It then provides explanations and examples of Faraday's first and second laws when a magnet and conductor are moving relative to each other. The document discusses dynamically and statically induced EMF, including the right hand thumb rule for determining magnitude and direction. Practical applications such as alternators and transformers are also covered. Maxwell's equations are derived and displacement current is explained using Ampere's law. The document concludes by discussing uniform plane wave propagation in charge free regions.
The document discusses various topics in electromagnetism including:
1) The magnetic force on a current-carrying wire due to the Lorentz force.
2) The magnetic field produced by different current configurations such as a straight wire, circular loop, and solenoid.
3) Magnetic induction and how a changing magnetic field can induce an electromotive force based on Faraday's law of induction.
This document discusses plane electromagnetic waves. It defines plane waves as waves whose wavefronts are infinite parallel planes of constant amplitude normal to the phase velocity vector. The electric and magnetic fields of a plane wave are perpendicular to each other and to the direction of propagation. Plane waves can be linearly, circularly, or elliptically polarized depending on the orientation and behavior of the electric field vector over time. Linear polarization occurs when the electric field is oriented along a fixed line. Circular polarization results when the electric field traces out a circle, and elliptical polarization is characterized by an elliptical trace.
This document discusses different types of antennas, including wire antennas like dipoles and monopoles, slot antennas, patch antennas, aperture antennas like horns, and reflector antennas like dishes. It provides details on common wire antennas like half-wave dipoles and folded dipoles. It also describes how antenna arrays work by controlling the amplitude and phase of fed elements to shape the radiation pattern through beamforming techniques.
Gen Phy 2 Q1L3 Electric Charge and Coulumb's Law.pptxJeffrey Alemania
* Given: q = 8.00 x 10-9 C
* Side of cube = 0.200 m
* Distance between charge and side = 0.141 m
* Area of each face = 0.200 x 0.200 = 0.0400 m2
* Using Gauss's law: φE = EA
* E = kq/r2 = (9 x 109 Nm2/C2)(8.00 x 10-9 C)/(0.141 m)2 = 4.80 x 105 N/C
* φE = (4.80 x 105 N/C)(0.0400 m2) = 1.92 x 10-3 Nm2/C
Therefore
Kelvin devised a method to determine the ohm using a rotating coil in a magnetic field. The resistance of the coil could be calculated based on the angle of a magnetic needle placed at the coil's center once it reached a stationary position. Rayleigh and Sidgwick used a similar setup with two disks rotated between coils to induce currents and measure resistance. Kelvin also created a current balance using six coils to directly measure current based on the forces induced between the coils. The document describes these three historical experiments and calculations to determine electrical units like the ohm and ampere based on fundamental standards of length, mass and time.
The document discusses the dual nature of matter and radiation. It provides answers to multiple choice and numerical questions related to photoelectric effect, de Broglie wavelength, and magnetic effect of current. Regarding photoelectric effect, it explains that electron emission from a zinc plate in ultraviolet light is due to the photoelectric effect. It also discusses how kinetic energy of photoelectrons varies with frequency of incident radiation. Regarding magnetic effect of current, it describes how to determine direction and magnitude of magnetic field around current carrying wires using the right hand grip rule. It also solves problems related to forces experienced by charged particles in magnetic fields.
- The document discusses magnetic fields created by electric currents. It covers the magnetic field of a moving point charge, the Biot-Savart law for calculating the magnetic field from a current-carrying wire, and an example calculation of the magnetic field from a long straight wire.
- The right hand rule is introduced for determining the direction of magnetic fields.
- Maxwell's equations for static magnetic fields in integral and differential form are presented.
- The document discusses magnetic fields created by electric currents. It covers the magnetic field of a moving point charge, the Biot-Savart law for calculating the magnetic field from a current-carrying wire, and an example calculation of the magnetic field from a long straight wire.
- The right hand rule is introduced for determining the direction of magnetic fields.
- Maxwell's equations for static magnetic fields in integral and differential form are presented.
Description of Physics of Optics, part I.
Please send comments and suggestions for improvements to solo.hermelin@gmail.com. Thanks.
For more presentations in optics and other subjects please visit my website at http://www,solohermelin.com.
From a circuit point of view, a transmitting antenna behaves like an
equivalent impedance that dissipates the power transmitted.
A receiving antenna behaves like a generator with an internal
impedance corresponding to the antenna equivalent impedance.
Magnetostatic fields are produced when charges are moving with constant velocity, such as in a current-carrying wire. Biot-Savart's law states that the magnetic field produced by a current element is proportional to the current and inversely proportional to the distance from the element. Ampere's law, the integral form of which relates the line integral of magnetic field around a closed path to the current through the enclosed surface, can be used to determine the magnetic field produced by symmetric current distributions.
The document discusses concepts related to electric charge, electric fields, and electric circuits. Some key points covered include:
- Charged objects exert forces on each other via an electric field according to Coulomb's law. The electric field is defined as the force per unit charge.
- Conductors allow free flow of electric charge while insulators do not. Resistors in circuits control current flow according to Ohm's law.
- Electric potential energy and voltage difference can be defined from the work done in electric fields. Equipotential surfaces exist where electric potential is constant.
- Electric current is the rate of flow of electric charge through a cross-sectional area of a conductor. Current, voltage, and resistance
Laboratory session in Physics II subject for September 2016-January 2017 semester in Yachay Tech University (Ecuador). Topic covered: electricity, magnetism
Based on Bruna Regalado's work
The document provides information about Vallurupalli Nageswara Rao Vignana Jyothi Institute of Engineering and Technology. It includes the vision, mission and quality policy of the institute which focus on producing global citizens through quality education and meeting technological challenges. The document also contains the lesson plan for the subject "Computer Organization" taught to third year students. The lesson plan details the prerequisites, objectives, outcomes, syllabus, teaching methodologies and assessment criteria for the course.
The document discusses various parameters that characterize antennas including frequency, radiation pattern, directivity, gain, beamwidths, sidelobes, impedance, radiation intensity, and polarization. It provides definitions and explanations of these key antenna parameters and includes diagrams to illustrate concepts such as radiation patterns, field regions, beamwidths, and units of antenna gain. The document aims to give an overview and introduction to fundamental antenna parameters needed to understand and design basic antenna types and their performance.
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1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
The document discusses several topics related to magnetic effects of electric currents:
1. Lorentz force law describes the force experienced by a moving charge in a magnetic field. Fleming's left hand rule indicates the direction of this force.
2. Instruments like galvanometers, ammeters, and voltmeters make use of the magnetic force on a current-carrying coil. Galvanometers can be adapted into ammeters using a shunt resistor or voltmeters using a series resistor.
3. Other topics covered include the magnetic field due to parallel currents, torque on a current-carrying coil, cyclotron particle acceleration, and the maximum energy attainable by particles in a cyclotron.
This document discusses circuit and network theory. It covers topics such as circuit elements and laws, magnetic circuits, network analysis, network theorems, AC circuits and resonance, coupled circuits, transients, two-port networks, and filters. Mesh analysis is introduced as a technique for network analysis that is applicable to planar networks containing voltage sources. The key steps are selecting mesh currents, then writing and solving KVL equations in terms of the unknown currents.
Cbse class 12 physics sample paper 02 (for 2014)mycbseguide
The document provides a sample physics question paper for Class 12 with 29 questions ranging from 1 to 5 marks. It includes questions from various topics in physics like electromagnetism, optics, modern physics, semiconductor devices, communication systems, and electrical circuits. The paper tests concepts, calculations, principles, diagrams, and applications of concepts across different areas of the physics syllabus. It provides guidelines for time, marks distribution and instructions for answering the questions.
This document discusses electromagnetic waves and applications of Faraday's laws of induction. It begins by outlining the learning objectives which include Faraday's laws, induced EMF directions and magnitudes, and practical applications. It then provides explanations and examples of Faraday's first and second laws when a magnet and conductor are moving relative to each other. The document discusses dynamically and statically induced EMF, including the right hand thumb rule for determining magnitude and direction. Practical applications such as alternators and transformers are also covered. Maxwell's equations are derived and displacement current is explained using Ampere's law. The document concludes by discussing uniform plane wave propagation in charge free regions.
The document discusses various topics in electromagnetism including:
1) The magnetic force on a current-carrying wire due to the Lorentz force.
2) The magnetic field produced by different current configurations such as a straight wire, circular loop, and solenoid.
3) Magnetic induction and how a changing magnetic field can induce an electromotive force based on Faraday's law of induction.
This document discusses plane electromagnetic waves. It defines plane waves as waves whose wavefronts are infinite parallel planes of constant amplitude normal to the phase velocity vector. The electric and magnetic fields of a plane wave are perpendicular to each other and to the direction of propagation. Plane waves can be linearly, circularly, or elliptically polarized depending on the orientation and behavior of the electric field vector over time. Linear polarization occurs when the electric field is oriented along a fixed line. Circular polarization results when the electric field traces out a circle, and elliptical polarization is characterized by an elliptical trace.
This document discusses different types of antennas, including wire antennas like dipoles and monopoles, slot antennas, patch antennas, aperture antennas like horns, and reflector antennas like dishes. It provides details on common wire antennas like half-wave dipoles and folded dipoles. It also describes how antenna arrays work by controlling the amplitude and phase of fed elements to shape the radiation pattern through beamforming techniques.
Gen Phy 2 Q1L3 Electric Charge and Coulumb's Law.pptxJeffrey Alemania
* Given: q = 8.00 x 10-9 C
* Side of cube = 0.200 m
* Distance between charge and side = 0.141 m
* Area of each face = 0.200 x 0.200 = 0.0400 m2
* Using Gauss's law: φE = EA
* E = kq/r2 = (9 x 109 Nm2/C2)(8.00 x 10-9 C)/(0.141 m)2 = 4.80 x 105 N/C
* φE = (4.80 x 105 N/C)(0.0400 m2) = 1.92 x 10-3 Nm2/C
Therefore
Kelvin devised a method to determine the ohm using a rotating coil in a magnetic field. The resistance of the coil could be calculated based on the angle of a magnetic needle placed at the coil's center once it reached a stationary position. Rayleigh and Sidgwick used a similar setup with two disks rotated between coils to induce currents and measure resistance. Kelvin also created a current balance using six coils to directly measure current based on the forces induced between the coils. The document describes these three historical experiments and calculations to determine electrical units like the ohm and ampere based on fundamental standards of length, mass and time.
The document discusses the dual nature of matter and radiation. It provides answers to multiple choice and numerical questions related to photoelectric effect, de Broglie wavelength, and magnetic effect of current. Regarding photoelectric effect, it explains that electron emission from a zinc plate in ultraviolet light is due to the photoelectric effect. It also discusses how kinetic energy of photoelectrons varies with frequency of incident radiation. Regarding magnetic effect of current, it describes how to determine direction and magnitude of magnetic field around current carrying wires using the right hand grip rule. It also solves problems related to forces experienced by charged particles in magnetic fields.
- The document discusses magnetic fields created by electric currents. It covers the magnetic field of a moving point charge, the Biot-Savart law for calculating the magnetic field from a current-carrying wire, and an example calculation of the magnetic field from a long straight wire.
- The right hand rule is introduced for determining the direction of magnetic fields.
- Maxwell's equations for static magnetic fields in integral and differential form are presented.
- The document discusses magnetic fields created by electric currents. It covers the magnetic field of a moving point charge, the Biot-Savart law for calculating the magnetic field from a current-carrying wire, and an example calculation of the magnetic field from a long straight wire.
- The right hand rule is introduced for determining the direction of magnetic fields.
- Maxwell's equations for static magnetic fields in integral and differential form are presented.
Description of Physics of Optics, part I.
Please send comments and suggestions for improvements to solo.hermelin@gmail.com. Thanks.
For more presentations in optics and other subjects please visit my website at http://www,solohermelin.com.
From a circuit point of view, a transmitting antenna behaves like an
equivalent impedance that dissipates the power transmitted.
A receiving antenna behaves like a generator with an internal
impedance corresponding to the antenna equivalent impedance.
Magnetostatic fields are produced when charges are moving with constant velocity, such as in a current-carrying wire. Biot-Savart's law states that the magnetic field produced by a current element is proportional to the current and inversely proportional to the distance from the element. Ampere's law, the integral form of which relates the line integral of magnetic field around a closed path to the current through the enclosed surface, can be used to determine the magnetic field produced by symmetric current distributions.
The document discusses concepts related to electric charge, electric fields, and electric circuits. Some key points covered include:
- Charged objects exert forces on each other via an electric field according to Coulomb's law. The electric field is defined as the force per unit charge.
- Conductors allow free flow of electric charge while insulators do not. Resistors in circuits control current flow according to Ohm's law.
- Electric potential energy and voltage difference can be defined from the work done in electric fields. Equipotential surfaces exist where electric potential is constant.
- Electric current is the rate of flow of electric charge through a cross-sectional area of a conductor. Current, voltage, and resistance
Laboratory session in Physics II subject for September 2016-January 2017 semester in Yachay Tech University (Ecuador). Topic covered: electricity, magnetism
Based on Bruna Regalado's work
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The document provides information about Vallurupalli Nageswara Rao Vignana Jyothi Institute of Engineering and Technology. It includes the vision, mission and quality policy of the institute which focus on producing global citizens through quality education and meeting technological challenges. The document also contains the lesson plan for the subject "Computer Organization" taught to third year students. The lesson plan details the prerequisites, objectives, outcomes, syllabus, teaching methodologies and assessment criteria for the course.
The document discusses various parameters that characterize antennas including frequency, radiation pattern, directivity, gain, beamwidths, sidelobes, impedance, radiation intensity, and polarization. It provides definitions and explanations of these key antenna parameters and includes diagrams to illustrate concepts such as radiation patterns, field regions, beamwidths, and units of antenna gain. The document aims to give an overview and introduction to fundamental antenna parameters needed to understand and design basic antenna types and their performance.
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1- Main Principles of Radiation_en.pptx
1. Antennas – G. Villemaud 0
4th year – Electrical Engineering Department
Guillaume VILLEMAUD
MAIN
PRINCIPLES
OF
RADIATION
2. Antennas – G. Villemaud 1
First considerations
Two important points:
Most of antennas are metallic
Huge majority of antennas are based on resonators
In a metal, by default the free electrons move erratically.
When creating a difference of potential (eg sinusoidal), the
internal field then controls the distribution of charges.
Currents and charges are then created as basic sources of
electromagnetic field.
But according to their distribution and relative phases, the
overall field delivered by a metallic element is the sum of all
contributions of these basic sources.
3. Antennas – G. Villemaud 2
Radiation mechanism
Charges transmitted over a straight metal at a constant
speed do not produce radiation.
+++
If the charges encountered a discontinuity (OC, bend ...) their
speed changes, then there is radiation.
+++
No radiation
Radiation
+++
High radiation
In a resonant structure, charges continuously oscillate,
creating a continuous stream of radiation.
4. Antennas – G. Villemaud 3
Loaded two-wire line
x
x
x
jβ
Be
jβ
Ae
i
Zr
Reminder on transmission lines:
x
Two-wire line closed on a load
superposition of an
incident and a reflected
wave
Without loss
5. Antennas – G. Villemaud 4
Open-ended two-wire line
y
r
ji
y
r
i
y
r
i
y
i
sin
2
jβ
e
jβ
e
Open-ended line:
y
t
y
Zc
r
v
t
y
i
cos
sin
,
Line with an open-circuit Stationary waves
O.C.
6. Antennas – G. Villemaud 5
Resonant line
y
r
ji
y
r
i
y
r
i
x
i
sin
2
jβ
e
jβ
e
t
y
Zc
r
v
t
y
i
cos
sin
,
C.O.
In practice, when the wires are relatively close, the currents are out of
phase, the total radiated field is close to zero (thank goodness).
Line with an open-circuit Stationary waves
7. Antennas – G. Villemaud 6
Bended wires
The classical approximation considers that if the arms of the line are
moved away, the current distribution remains the same.
8. Antennas – G. Villemaud 7
Radiating dipole
Then we have
inphase currents
for effective
radiation: the
principle of the
dipole antenna
Problem: in practice, there is
mismatch. Then we seek a resonant
antenna having an input impedance
matched to a progressive wave line.
9. Antennas – G. Villemaud 8
Reminder on EM fields
To study phenomena of electromagnetic wave propagation, a
medium will be defined by:
Its complex electrical permittivity
'
'
'
j
Its complex electrical permeability
Its conductivity
(F/m)
'
'
'
j
(S/m) electrical loss
Medium characteristics:
10. Antennas – G. Villemaud 9
Radiation sources
Currents and charges present in this medium are called
primary sources:
Surface current density
Volume charge density
These sources create:
p
I
Electric and magnetic fields
Other currents and charges
(A/m²)
p
Q (Cb/m3)
E (V/m)
H (A/m)
c
I c
Q
and
Induction phenomena
11. Antennas – G. Villemaud 10
Maxwell’s Equations
In an isotropic and homogeneous medium, we
obtain these equations :
0
b
div
q
d
div
e
i
e
d
t
e
e
h
rot
h
b
t
h
e
rot
c
c
Sources can be distributed as linear, surfacic or volumic
densities.
12. Antennas – G. Villemaud 11
Resolution domain
Two distinct areas solving these equations are
considered: in the presence of charges and currents
or out of any charge or current.
The resolution in the presence of charges and currents
is used to determine the field distribution produced by a
linear, surface or volume charges and currents (which
leads to the radiation pattern of the antenna).
The second type of resolution is required to calculate
the electromagnetic waves propagated in free space (or
in a particular medium).
13. Antennas – G. Villemaud 12
Sinusoidal source
Still in the case of homogeneous and isotropic
media, with harmonic source the following
equations are obtained:
0
B
div
Q
D
div
E
j
E
H
rot
H
j
E
rot
C
Then we can solve these equations to determine
the field produced by the charges and currents
present on a conductor.
14. Antennas – G. Villemaud 13
Relation to the surface
The electric field is always
perpendicular to the conductor.
The magnetic field is always tangent
to the conductor.
The electric field is proportional to the
charges on the surface.
The magnetic field is proportional to
the surface current.
Interface with a perfect conductor
1, 1, 1
1
E 1
H
0
.
.
0
1
1
1
1
H
n
Q
E
n
I
H
n
E
n
S
S
15. Antennas – G. Villemaud 14
EM potentials
To assess the effects of an isotropic source at a
point P of space we can introduce the vector and
scalar potentials:
)
,
(
)
,
( t
r
A
t
r
B
t
)
t
,
r
(
A
)
t
,
r
(
V
)
t
,
r
(
E
0
B
div
Knowing that we can write
o
x
y
z
P
r
q
j
Vector A is defined in a gradient
approximate, then there is a function
V satisfying:
16. Antennas – G. Villemaud 15
EM potentials
Expressing Maxwell's equations based on the
potential, we obtain the wave equations:
L
r
j
l
L
r
j
l
dl
r
e
r
I
A
dl
r
e
r
Q
V
.
)
(
4
.
)
(
4
1
0
Scalar potential
Vector potential
Q
t
V
V
2
2
2
I
t
A
A
2
2
2
The resolution (based on the complex Green's
functions) provides for a linear distribution:
17. Antennas – G. Villemaud 16
Elementary source
The Hertzian electric dipole is a linear element,
infinitesimally thin, of length dl (<<l) where we can
consider a uniform distribution of currents (infinite
speed).
+q
-q
i(t)
r
P
q
z
x
)
r
(
E
r0
r1
This is a theoretical tool to predict the behavior of any antenna as
the sum of elementary sources.
t
j
Qe
charges
Q
j
currents
18. Antennas – G. Villemaud 17
Radiated field calculation
The problem is rotationally symmetrical relative to Oz.
The vector potential has only one component Az:
The magnetic field has just one component:
r
e
dl
I
Az
r
j
m
.
.
4
Then we obtain:
H
0
r
H
0
q
H
2
1
.
sin
.
.
4
1
r
r
j
e
dl
I
H r
j
m
q
j
j
H
19. Antennas – G. Villemaud 18
Electric field calculation
Then we can deduce the electric field which is produced :
Electric field with two components: and
E
3
2
1
.
cos
.
.
2
1
r
j
r
e
dl
I
E r
j
m
r
q
0
j
E
3
2
1
.
sin
.
.
4
1
r
j
r
r
j
e
dl
I
E r
j
m
q
q
r
E q
E
So we end up finally with three components of the radiated
field.
Depending on the distance from the observation point P with
respect to the source, we will do different approximations to
simplify expressions.
20. Antennas – G. Villemaud 19
Approximations depending on r
3
2
1
.
cos
.
.
2
1
r
j
r
e
dl
I
E r
j
m
r
q
3
2
1
.
sin
.
.
4
1
r
j
r
r
j
e
dl
I
E r
j
m
q
q
2
1
.
sin
.
.
4
1
r
r
j
e
dl
I
H r
j
m
q
j
The terms in 1/r represent the radiated field
(predominant when large r) 1/r2 terms give the induced
fields and terms in 1/r3 the electrostatic field.
21. Antennas – G. Villemaud 20
Zones of radiation
Emitter
Feeding line
Very near zone
(some wl)
Plane
waves Wave
surfaces
Near field zone
(Fresnel) Far field zone
(Fraunhoffer)
Wave
surfaces
Spherical
waves
Antenna
22. Antennas – G. Villemaud 21
Zones of radiation
Fluctuating
Quasi-constant Decreasing in 1/r²
23. Antennas – G. Villemaud 22
)
(
)
(
sin
2
)
,
(
sin
2
)
,
(
r
t
j
r
t
j
e
dl
I
r
j
t
r
E
e
dl
I
r
j
t
r
H
q
j
q
l
q
l
377
120
)
,
(
)
,
(
q
o
o
t
r
H
t
r
E
Hertzian dipole’s radiation
Far field approximation :
Free space
i(t)
24. Antennas – G. Villemaud 23
Farfield Propagation
0
0
B
div
D
div
E
j
H
rot
H
j
E
rot
Returning to the harmonic equations in the case of
homogeneous, isotropic media containing no
primary sources, we obtain the following equations:
Remark : In this case, we see that the equations in E and H are
almost symmetrical, the only difference being the absence of
charges and magnetic currents. We can then introduce fictitious
magnetic sources for these symmetrical equations. The solution of
the electrical problem then gives the magnetic problem solution and
vice versa.
25. Antennas – G. Villemaud 24
Propagation equations
The propagation equations for the fields E and H (expressed in
complex instantaneous values) are written as follows:
0
2
2
t
E
E 0
2
2
t
H
H
If propagation is in the direction Oz, it comes:
and
The ratio represents the propagation speed of the wave.
Knowing that generally we consider that (except for ionised or
magnetic medium) we can write :
0
2
2
2
2
t
E
z
E
0
2
2
2
2
t
H
z
H
1
v
1
r
n
c
c
1
1
v
r
r
0
0
26. Antennas – G. Villemaud 25
Solutions
In a sinusoidal steady state regime, these equations admit solutions of the
form:
and
with : (wavenumber)
The ratio between absolute values of and represents the wave
impedance of the considered medium (in ohms):
it’s a real value.
)
kz
t
(
j
exp
E
)
t
,
z
(
e
)
kz
t
(
j
exp
H
)
t
,
z
(
h
l
2
v
k
E H
H
E
In the air: 377 ohms
u
H
E
We have a fundamental relation:
27. Antennas – G. Villemaud 26
Spherical wave –Plane wave
A point source (Q charge) produce radiation of a
spherical wave.
Indeed, solving the equations of potential in the case of a
point source is symmetrical spherical revolution, and
gives solution for:
2
1
.
4
1
)
(
r
r
j
e
Q
r
E r
j
In Farfield, this leads to:
r
j
e
r
Eo
r
E
)
(
The wave surface is a sphere centered at the point source
28. Antennas – G. Villemaud 27
Plane wave approximation
Propagation direction
E
H
l
z
d
z
t
E
E
cos
0
Solutions of Maxwell's equations are numerous (depending
on the initial conditions).
All can be expressed as the sum of plane waves.
29. Antennas – G. Villemaud 28
Carried power
When the far field condition is satisfied, the wavefront can
be assimilated to a plane wavefront. The power carried
by the wave is represented by the Poynting vector:
*
H
E
2
1
P
x
y
z
E
E
H
31. Antennas – G. Villemaud 30
Polarization of the wave
We know that far-field E and H are perpendicular to each
other and perpendicular to the direction of propagation.
But depending on the type of source used, the orientation of
these vectors in the plane wave can vary.
Based on the variations in the orientation of the field E over
time, we define the polarization of the wave.
In spherical coordinates, the components of the E field of a
plane wave is described by:
j
j
q
q u
E
u
E
E
a
t
A
E
q
sin
b
t
B
E
j
sin
with and
32. Antennas – G. Villemaud 31
Linear polarization
First hypothesis: components pulse in phase
b
a
j
q
u
B
u
A
t
E
sin
Several possibilities:
horizontal, vertical or slant
polarization
q
E
j
E
E
animation
33. Antennas – G. Villemaud 32
i(t)
Linear vertical polarization
Example with hertzian dipole
34. Antennas – G. Villemaud 33
i(t)
Linear horizontal polarization
35. Antennas – G. Villemaud 34
i(t)
Slant linear polarization
Example with 2 inphase dipoles
36. Antennas – G. Villemaud 35
Circular polarization
Second hypothesis: components vibrate in phase quadrature
and magnitudes are equal
2
a
b
j
q
u
a
t
u
a
t
A
E
cos
sin
q
E
j
E
E
37. Antennas – G. Villemaud 36
i(t)
Circular polarization
39. Antennas – G. Villemaud 38
Illustration of Circular polarization
40. Antennas – G. Villemaud 39
3 modes of polarization
– Linear polarization
• vertical, horizontal, slant (plane H or E)
– Circular polarization
• Left-hand or right-hand
– Elliptic polarization
• General definition
Elliptic Polarization
41. Antennas – G. Villemaud 40
Fundamental theorems
To study the functioning of antennas, four fundamental
theorems are known:
the Lorentz reciprocity theorem
the theorem of Huygens-Fresnel
the image theory
Babinet's principle
42. Antennas – G. Villemaud 41
Lorentz reciprocity
If we consider that two distributions of currents I1 and I2 are
the source of E1 and E2 fields, Maxwell's equations allow to
write:
v
v
dv
I
E
dv
I
E .
.
.
. 2
1
1
2
radiating systems are reciprocal (note only in
passive antennas).
Pf Pr
Pf
Pr
43. Antennas – G. Villemaud 42
Huyghens-Fresnel’s principle
Principle for calculating the radiation at infinity of
any type of source
sources
Arbitrary surface
No field
equivalent surface
sources (electric
and magnetic)
44. Antennas – G. Villemaud 43
Application to radar
Principle for bistatic radar
target
The field received in P is the sum of the field that would be
received without the obstacle (known) and diffracted by the
obstacle. It is then possible to calculate the inverse of the
surface formed by sources providing such a field.
Plane wave
Observation
point
P
45. Antennas – G. Villemaud 44
Image theory
At an observation point P, the field created by a source + q
placed above a perfect ground plane of infinite dimensions is
equivalent to the field created by the combination of this
charge with its image by symmetry with a charge -q.
+q
P
x
+q
P
x
-q
46. Antennas – G. Villemaud 45
Image of currents
The same principle applies to the current sources.
The image is formed by the symmetry of the current
distribution of opposite sign (phase opposition).
P
x
P
x
I I
I
This is the basis for many applications in antennas
47. Antennas – G. Villemaud 46
Babinet’s principle
Babinet's theorem shows the symmetrical appearance
of Maxwell's equations.
E
H
case 1
case 2
The total field of case 1 will be equal to the
diffracted field in case 2 and vice versa.
48. Antennas – G. Villemaud 47
Application to antennas
Any slot in a ground plane of large dimension will have
the same behavior that the equivalent metallic antenna
in free space except that the E and H fields are
reversed.
E H