Hello and welcome to NPTEL MOOC, this is a
course called Electromagnetic Wave Propagation
in Guided and Wireless Media.
The course ID of this particular course which
will be offered in the January, 2019 session
is E21.
And My name is K. Pradeep Kumar and I am associate
professor in the department of Electrical
Engineering at the Indian Institute of Technology,
Kanpur and I am the instructor of this course
which as I have told you Electromagnetic Wave
Propagation in Guided and Wireless Media.
What is this course about?
Now, the title of the course of course gives
you the picture of what the contents of the
course could be.
The main concern in this course is to study
the Electromagnetic Wave Propagation in 2
kinds of media, one is what is called as guided
media which encompasses all those media in
which physically their exist structure which
help the wave to be propagated from point
A to point B, those are called as guided media
and those media where there is no physical
structure but electromagnetic waves are still
taken from point A to point B except that
we don’t really call it as propagation,
the correct word would have been radiation.
I didn’t want to put both words in the same
title so therefore I essentially said that
there is electromagnetic way propagation in
guided and wireless media, wireless media
would mean media where there are no you know
physical structure which takes electromagnetic
waves from one point and to the other point.
Examples of guided media in which there are
physical structures, which guide electromagnetic
wave from point A to point B are the familiar
transmission lines, the microwave wave guides,
optical wave guides and optical fibers.
Example of wireless media, of course there
is no physical media as such but you may have
heard of antennas being emitting radiation
and antennas also absorbing the part of radiation
where the electromagnetic waves are propagating
in air or you know even in deep space as such,
right.
And it also encompasses propagation of electromagnetic
waves in the form of free space optics meaning
you have a light source and then you have
a lens and light actually propagates between
the media, in air or in any other kind of
a media but there is no physical structure
of that.
The goal of this course is to treat in some
uhh deeper context of the transmission lines,
microwave and optical wave guides and optical
fibers, these collectively are the guided
media and then only talk a little bit about
antenna basics and free space optical wave
propagation, both of which are very important.
And to finally look at what is called as wireless
channel modelling, so this will be a brief
topic in which we are going to study how to,
means we will apply the ideas of propagation
and radiation and then see how electromagnetic
waves propagate and how do we model that in
free space and this wireless channel modelling
is of course very important for wireless communications
as such, right.
If you look at this slide I have put in these
different guided media, all pictures taken
from Internet of course, so what you can see
here is that on the X axis down below is the
increasing way of frequency and the axis on
the top here which is again along the X axis
but the corresponding numbers are in the wave
length, right.
Now we know that wavelength time frequency,
means it is constant which of course depends
on the media but in free space that value
will be equal to the speed of propagation
so if you want to obtain the corresponding
wavelength or corresponding to a given frequency,
all you have to do is to divide the frequency
or rather divide the speed of propagation
C which is 10 to the power 8 meter per second
by the frequency value to get the wavelength.
Wavelength is measures in meters; frequency
is measures in hertz.
And this engineering units of kilo hertz,
megahertz, gigahertz, terahertz, are the multi
players that we associate with the basic frequency
measurement.
So, you can see here on the left most corner
where in terms of frequency where somewhere
between 30 hertz to 300 hertz is the power
line cable, right.
So, these cables are something that you might
have seen, you will see them in every place
on Earth where there is electricity kind of
distributed.
So, these lines are very long, they actually
cover the entire country and sometimes cove,
I mean cover bigger country as of course,
in continents they may actually even pass
through different country, so these power
line cables are essentially very-very long
cables and their function is to transport
energy or transmit energy from one point to
another point and they are actually transmitting
the electromagnetic energy of course at such
low frequencies we actually talk about voltages
and currents to therefore we can call them
as voltage transmission lines or current transmission
lines or simple power line cables because
they actually transport the voltage and current,
the product in some sense gives you the power,
right.
So, but what you have note is that these frequencies
are very low, in India they are about 50 hertz,
in US and in some other parts of the world
they are about 60 hertz and the corresponding
wavelength is actually very large, right,
because these are in hertz, the corresponding
wavelengths are in 100 kilometers, okay.
Moving up in the frequency axis you will see
that there is a coaxial cable which is another
structure and this coaxial cables are something
that you have used in all of your laboratories,
right and you also have used this coaxial
cables to connect up the dish antenna to your
television sets and these coaxial cables contain
one inner conductor and one outer conductor
and they normally operate anywhere from low
frequencies, something around 3 kilohertz,
all the way up to a few megahertz, around
30 megahertz, 40 megahertz, and good quality
connectors and coaxial cables may even go
up to a few gigahertz frequency range region.
So, these are coaxial cables which we are
going to study in some length in the course.
Then you see a certain set of components which
are grouped here, their frequency ranges are
anywhere from 13 megahertz all the way up
to gigahertz, beyond that their performance
deteriorate significantly and these lines
essentially consists of the same two wires
just as in a power line cable or a coaxial
cable but the geometry of these lines are
very different, in fact they are not really
called as lines, these microstrip lines that
we talk about is mostly commonly found on
printed circuit boards, so if you tear open
your cell phone and then you know break it
open to see the printed circuit boards that
forms the body of the cell phone, you will
actually see many-many lines running in this
particular form, so these top one which is
shown with W, with a width of W is called
as a trace and then these are the variations
of the micrstrip line, this is called as strip
line, buried stripline, and then you know
coplainer wave guides and what on, whatever,
whatever.
So, these are mainly used in printed circuit
boards and their region of operation is typically
about 30 megahertz to 3 gigahertz, right.
When you increase frequency further that is
you go into tons of you then end up in the
band which is actually called as millimeter
wave band and one of the important things
that is coming up today is the millimeter
wave system which are expected to be employed
by wireless networks as well but if you want
to connect electromagnetic energy or rather
transport magnetic energy from point A to
point B at these frequencies, in these tons
of gigahertz and hundreds of gigahertz, you
have to use what are called as microwave wave
guides or just wave guides, right.
These are hollow tubes of different cross
sections for example, you can see here there
is a twist dead cross section or you know
the kind of a twist that you can see and you
can see the straight wave guide with a rectangular
cross section, I have not shown here but you
will also find this wave guides in the circular
cross section and pretty much any kind of
a geometry which of course is determined by
many other parameters can be made to work
and these microwave wave guides are essential
used to guide energy from point A to point
B in the region around 10s to 100s of gigahertz,
but please note that their lens cannot be
usually very-very large going to the simple
fact that they become very expensive if you
want to use them.
Very economical and most powerful way of conveying
uhh electromagnetic energy from point A to
point B, at the optical frequencies, right
at very high frequencies is given by these
2 examples one is called as an optical wave
guide and the other one is called as an optical
fiber, an optical wave guide is one which
is used in many integrated optical circuits
and optical fibers of course as you know already
are laid out pretty much everywhere on, I
mean pretty much at every place on Earth and
these optical fibers which are very tiny strands
of dielectric materials, made out of dielectric
material can carry large amount of information
and this information is actually in the form
of electromagnetic wave which are changing
with respect to time and therefore information
is being propagated from point A to point
B.
And here we are really talking about distances
which are like intercontinental distances
like thousands of kilometers long optical
fibers and the corresponding frequencies are
of course in a few tons of, tons to hundreds
of terahertz, the frequency access is kind
of logarithmically placed so therefore the
frequency rapidly as we go around, right?
So, but I would like you take a minute to
look at this entire slide and then realize
such an important point that almost all of
these guiding behavior will be given by a
very few set of equations called as Maxwell’s
equations, and of course we have to apply
Maxwell’s equations under different approximation
to describe the propagation of electromagnetic
waves but it is very surprising that some
frequencies which are just a few hertz all
the way up to tons and 100s of terahertz,
is actually covered by Maxwell’s equation,
right.
So, that is the beauty of Maxwell’s equation
which form the basis of studying electromagnetic
waves guided by these structures, please note
that I am using the word structure, the meaning
of that will become clear in the first lecture
that we are going to have after this introduction,
right.
And to just summarize the wireless media,
I know I have just picked up some pictures,
we are going to look at few basics of antennas,
this is a dish antenna that you might have
seen, uhh everywhere and these are the fields
which are radiated, note that these fields
keep travelling in air and then there will
be a receiving antenna which will intercept
and then convert some of that electromagnetic
wave into voltages and currents and if there
is some information contained in this field,
you will also get that information in the
receiving antenna
.
And the corresponding problem as you increase
the frequency further up and up or the wave
length reduce to such a small extent are the
effects which are called as diffraction effects
that will come up when optical waves, so these
are optical waves, the specific reasons why
there are these lines, we will look at it
later on, and they try to pass through an
aperture they tend to spread out and this
phenomena is called as diffraction and we
are going to look at what diffraction is and
how this diffraction in fact is a fundamental
component of all of this wireless channel
model.
So, here you have a base station tower and
then you have a cell phone and there are lot
of buildings and in this particular landscape
there is also a mountain and you can see that
this blue line corresponds to a light of electromagnetic
wave coming straight from the base station
to the cell phone whereas the other waves
are all actually diffracted, reflected and
so on, right.
So, the phenomenon that we are going to study
in diffraction will be directly applicable
for wireless channel model, okay.
So, this is in essence the course content
briefly, we are going to start with transmission
lines and then we will look at applications
of transmission lines.
Our focused will be to consider you know applications
for signal integrity, and to study those specific
problems that come up when you try to make
printed circuit boards and try to drive signals
from there printed circuit boards.
Then we move on to electromagnetic waves in
free space, we are going to look at a few
mathematical techniques of describing electromagnetic
wave in free space and then apply those techniques
to study diffraction of electromagnetic waves
and then we come back to guided structures
and then we will look at guided wave in metallic
wave guides, those cross section microwave
wave guides that I talked about and then we
extend that one to dielectric waveguides and
finally we talk a little bit about radiation,
some part of the radiation we would have already
considered in the free space electromagnetic
in the week 3 as well so we are going to supplement
that with week 7 of fundamentals of radiation
and finally close by talking about wireless
channel modelling, right.
The textbooks that I have here are you know
just the suggested textbooks, one the webpage
I will upload much more number of textbooks
and references.
The textbook that I would recommend if you
can get hold of these textbooks is the second
one Electromagnetic Waves by David Staelin
and others and this is now available in the
Indian edition as well, it pretty much covers
all of the topics that I have shown here in
this slide except for wireless channel modelling
which anyway suggest some more literature
for you and there are other references which,
are some of them are very comprehensive references,
we probably will not be required to look at
all of them in that details, oaky.
So the goal here just to reiterate is to understand
electromagnetic waves, and then to see these
different structures, which guide electromagnetic
waves and to see what are the specific problems
that come up when you are going to use these
structures to guide electromagnetic waves,
this topic is very important, and the pre-requisites
for this topic is I mean this course, is that
you should have had first course in electromagnetic
theory.
I also given have given NPTEL courses on electromagnetic
theory, I would recommend strongly to study
any of those uhh, to study some of those videos
to view some of those videos and to know little
bit about Maxwell’s equations and boundary
conditions at least until the start of the
third week, right.
So, with this let me close and I hope that
you will enjoy this course and we will have
more details to share on the websites, so
please look at the website periodically for
more details.
Thank you very much!
