is a subject which has fascinated human beings over many more centuries. In ancient days

people used to ask questions like why the stars twinkle and the planets do not twinkle

or why there is lightening or if I put a magnetic needle in certain environments why the magnetic

needle deflects, how does the light reach from sun to the earth when there is no medium

in between. These kinds of questions people try to investigate form many more centuries.

In the modern days people have questions like how do we have a TV reception, how do we have

a Radio station operating, how does the mobile phone works, why the TV reception is good

in some part of the house and it is not good in some other part, why we do not have a good

Radio reception inside a Railway compartment, why the Radio station which at medium waves

does not show any time fluctuation where as Radio station which is operating at short

waves has time fluctuations, why certain things get heated when they are kept inside microwaves

and there are numerous phenomena which you see in modern days which fascinate the common

man.

All this phenomena either you take ancient phenomena or you take modern phenomena the

common thread which runs through all these phenomena is Electromagnetism. In fact in

today's world if we look around there is hardly any gadget which does not work on Principles

of Electromagnetism.

In this course of Electromagnetic Waves essentially we are going to investigate the high frequency

aspects of Electromagnetism. Broadly an electromagnetic phenomenon can be divided into two categories

which are low frequency but high power and high frequency but low power.

So the phenomena like electrical machines, electrical power generation transformers and

distribution of electrical energy are fall in the category of high power but low frequencies.

Where as if you go to the modern systems like Mobile Communications, Radars Satellites,

Optical fibers fall in the category of low power but high frequencies.

In this course, essentially we are going to develop the Principles of Electromagnetics

at high frequencies. We can ask very basic questions like if the frequencies increases

what way the electrical phenomena or the understanding which we have from low frequency circuits

get modified and then we can understand the various phenomena which I have mentioned which

have a common thread is Electromagnetic Waves.

So electromagnetic waves essentially seek applications in many areas. Firstly, we have

applications in Transmission Lines and a High Frequency Circuits like Radars or TV's or

Radios.

Then we have application of electromagnetic waves in the area of Antennas which can either

transmit electromagnetic energy or can receive electromagnetic energy. We require knowledge

of electromagnetic waves in a subject called Satellite Communication, we require knowledge

of electromagnetic waves in the area of Fiber Optic Communication and we require this knowledge

in Cellular wireless Communication and applications in Radars and classical subject like Radio

Astronomy and also subjects related to Electromagnetic Interference and Electromagnetic Compatibly.

So in this course essentially we will try to investigate how time varying electric and

magnetic fields behave especially when the frequency of operation is large. As we all

know that in general the phenomenon of Electromagnetism is governed by the four classical equations

called the Maxwell's Equations. The Maxwell's equations represent the phenomena of Electromagnetism

in totality. However as we proceed in this course every time it is not required to go

to the regress analysis of Maxwell's equations and under certain approximations we can investigate

the same phenomena in terms of voltages and currents in terms of electrical circuits,

however as we go further we will find the representation of this in terms of voltages

and currents become difficult. then we can move to the general phenomena of electric

and magnetic fields.

Let us first look at the Electromagnetic Spectrum.

The word the electromagnetic wave corresponds to any phenomena which were related to the

time varying signals time varying electric or magnetic fields. So no matter how small

the frequency is, any frequency which is not zero can be put in this category of time varying

electromagnetic fields.

So what is shown here are the wavelengths and the physical dimensions which normally

are corresponding to those wavelengths. So if we go to very low frequencies the Radio

frequencies the wavelength is very large and it is comparable to size of a building. When

you go to the microwave frequencies the wavelength becomes about a few centimeters which is typically

of the side of an insect, as you go further the wavelength reduces then the size becomes

tip of the needle. When you go to visible range of the Electromagnetic Spectrum then

essentially you are talking about size of the atoms or molecules and when you go to

X-rays and γ-rays the wavelength becomes smaller or comparable to the atoms. So the

entire frequency range from very low frequencies to high frequencies can be summarized in one

word that is the Radio frequency.

So in this course when we refer to Radio frequency essentially we are referring to any phenomena

which is not constant as the function of time but it has a finite frequency. The same thing

can be written in more technical terms that here we have got the Electromagnetic Spectrum

these are the wavelengths starting from about 10 meters to one meter then ten centimeters

to one centimeter and to one millimeter

and all the way we go up to about 0.1 micro meters which will be typically in the range

of what X-rays and these are the corresponding frequencies. So ten meters would correspond

to thirty meters, ten centimeters would correspond to three Giga hertz and like that when we

go to this region where the wavelength is typically about order of one micro meter the

frequency will be typically of the order of about 300 Tera hertz. Then depending on the

frequency of operation we use different media for transmission of these signals so in this

region we use the media called the Coaxial cables. Where as when you go to this range

of wavelengths we use structure called the Waveguides and when you go to the very high

frequencies in optical domain then the media will be Optical Fibers.

One can ask a very basic question at this point that why do we have to go to high frequencies?

What advantage one gets by increasing the frequency? What one noticed is if you consider

a typical electrical system then the bandwidth of the system is more or less proportional

to the frequency of operation. If we consider the major application of high frequencies

as communication then we require large bandwidth for transmitting more information. So as we

can see from here the Band Width is proportional to the frequency, one can get larger bandwidth

by increasing the frequency of operation therefore one can transmit more information on a given

channel.

So from information transfer point of view, increasing the frequency provides larger bandwidth

and it is increasing the capacity of the information transmission.

So the first application which we have for the Electromagnetic Waves is Transmission

Lines in which essentially we investigate how the voltages and currents are going to

flow in a two conductors system called a Transmission Line.

so a simpler system which we see all around for connecting any electrical signal from

one point to another we require a pair of wires and these pairs are twisted so this

medium is called Twisted Pair.

Now we will see this kind of medium is normally used for Telephone Lines and we want to investigate

how the electrical signals will propagate on this structure. This media the twisted

pair can handle low data rates, has a high Electromagnetic Interference and is very lossy

as the frequency increases. So normally this medium is very useful for low frequencies

but as the frequency increases the loss increases and that is why this medium became not very

attractive.

As the frequency increases we go for a medium called a Co-axial cable where we have a center

conductor here and then you have outer conducting shell the high frequency signals are applied

between the center conductor and the outer shell and the signal flows inside this empty

region here. This cable structure can handle data rates which could be typically about

the order of few megabits per second, has low electromagnetic interference and also

has moderate loss. So we require fundamentals of Electromagnetic Waves to investigate propagation

of energy on this structure.

As the frequency increases even the center conductor of a Co-axial cable adds to sufficient loss

and therefore the surface area of the conductor is minimized.

And in this process essentially we end up into a hollow pipe of metal inside where the

electromagnetic waves can propagate. This structure is called a Waveguide.

If the cross section of this hollow pipe is rectangular then we see that this Waveguide

is called the Rectangular Waveguide. On the other hand if the cross section of this pipe

is circular then we call this as a Circular Waveguide. So at high frequencies typically

at microwaves the hollow pipes made of metal are used for guiding the electromagnetic energy.

And again you require a rigorous analysis of electromagnetic wave propagation inside

these conducting pipes which helps you in finding out what will be the field distribution

inside this structure, how much energy loss will take place when it propagates inside

this and so on.

The next application of Electromagnetic Waves is Antennas. The antenna is a device which

can transmit electromagnetic energy into the space and also it can receive electromagnetic

energy coming from the space.

So, many modern types of equipment are using the Antennas. Here you can see an Antenna

called a Parabolic Dish in which radiation falls on this dish gets reflected from here

and then here there is something called the feed.

The Electromagnetic Waves get focused on to this point and then it gets converted into

electrical signal and that electrical signal is processed further. The same dish will generate

electromagnetic wave if the electrical system is supplied to the feed, which will get reflected

from this and it will get into the Space.

So Antenna is a device which selectively puts the radiation in the desired direction. In

fact a simple Antenna structure may not really provide the directional characteristics of

radiation.

Also in modern days we have got the Smart Antenna Systems where the radiation characteristics

of the Antenna are automatically changed to maximize the reception of the signal. So we

require a thorough knowledge of electromagnetic wave propagation in the analysis of Antenna

or the Smart Antennas.

Here is another Smart Antenna System which has not one beam but have multiple beams and

these beams can be switched or they can be placed inside this space on permanent basis.

And one can transmit the signal or can receive the signal from that zone depending upon which

area the observer is. So controlling the radiation characteristics is one of the important aspects

of Antennas.

The next area where you require a thorough knowledge of Electromagnetic Waves is the

Satellite Communication. The Satellite is an object which is placed above the earth's

surface. So here you can see the Satellite picture.

This is the earth and this is the Satellite where this picture is taken from the Satellite

towards the earth. And this is the station called a Earth Station.

The transmitted signals from the earth to the Satellite and from the Satellite to the

earth are received by this station.

There are certain frequency bands assigned for Satellite communication called C-Band,

S-Band, X-Band, K-Band and Ku-Band.

So in this mode essentially we have electronic systems here with an Antenna and we are having

our station here, the signal is transmitted from the Earth towards the Satellite.

The satellite receives this signal converts its frequency and then sends it down towards

the earth and this signal which is coming towards the earth can be received by the receiving

stations on the earth. So one can establish a communication between one point on earth

to any other point on earth. This whole propagation of electromagnetic radiation and proper placing

of radiation in a direction towards the earth is controlled by the electromagnetic wave

phenomena.

So, essentially again we require a good understanding of the propagation of Electromagnetic Waves

in investigating of propagation of energy from ground to Satellite and from Satellite

to ground. The Satellite is one of the modern communication transmission devices which have

a relatively large bandwidth, it can transmit the data which can be itself monitored and

it provides you a mobile environment. So in fact Satellite was one of the modes of transmission

with a large bandwidth before the Optical Fiber came.

Later as the time progress the Fiber Optic Communication came.

Then the knowledge of Electromagnetic Waves is required for investigating the propagation

of light inside the Optical Fiber.

Here you can see a set of optical fibers having a very thin structure which is made of glass

through the light is propagated. And we require a good theoretical understanding of propagation

of light inside this because the signal gets distorted as the light propagates inside the

Optical Fiber. Unless we understand fully how the signal get distorted one will not

be able to tell how efficiently or properly the data can be transferred on this medium

which is Optical Fiber.

Similarly the devices which are used for optical communication which are lasers again require

a good knowledge of electromagnetic waves. Then when we come to the Wireless Communication

which is the most modern mode of communication, again you require various aspects of electromagnetic

waves.

Here you can see father of Radio Communication is Hertz, he is doing some measurement on

radiation. This is an environment where there are lot of gadgets which all works on electromagnetic

wave principle, this is a mobile phone

So all this together we will see today in a mobile environment all these devices are

working on principles of Electromagnetic Waves.

In this modern communication called a Cellular Communication we have the base stations from

where the signals are transmitted and then you arrange users which are located inside

a cell.

So any mobile call which we make goes from handset towards base station and then the