microwave and electromagneticsmakes the electromagnetic spectrum is depicted in the following...
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Code No. Subject Semester No.
17ELU12 MICROWAVE AND FIBER OPTIC COMMUNICATION IV
Microwave and Electromagnetics
Unit I
Microwave region and band designations - Advantages & Applications of Microwave – E.M wave principles- Maxwell’s Equations: Amperes Law – Faraday’s Law – Gauss’s Law – Wave Equations – TEM/TE/TM/HE wave definitions.
10
Microwave Frequency Bands
The microwave spectrum is usually defined as a range of frequencies ranging from 1 GHz to over
100 GHz. This range has been divided into a number of frequency bands, each represented by a
letter. There are a number of organizations that assign these letter bands. The most common being
the IEEE Radar Bands followed by NATO Radio Bands and ITU Bands. Below you can see tables
with details on each letter band. Click on the letter band to learn more about it and find products
on everything RF that can be used for in this band.
Frequency Bands
Frequency Band Frequency Range Wavelength Range
L band 1 to 2 GHz 15 cm to 30 cm
S band 2 to 4 GHz 7.5 cm to 15 cm
C band 4 to 8 GHz 3.75 cm to 7.5 cm
X band 8 to 12 GHz 25 mm to 37.5 cm
ELECTROMAGNETIC WAVE SPECTRUM:
Electromagnetic Spectrum consists of entire range of electromagnetic radiation. Radiation is the
energy that travels and spreads out as it propagates. The types of electromagnetic radiation that
makes the electromagnetic spectrum is depicted in the following screenshot.
Ku band 12 to 18 GHz 16.7 mm to 25 mm
K band 18 to 26.5 GHz 11.3 mm to 16.7 mm
Ka band 26.5 to 40 GHz 5.0 mm to 11.3 mm
Q band 33 to 50 GHz 6.0 mm to 9.0 mm
U band 40 to 60 GHz 5.0 mm to 7.5 mm
V band 50 to 75 GHz 4.0 mm to 6.0 mm
W band 75 to 110 GHz 2.7 mm to 4.0 mm
F band 90 to 110 GHz 2.1 mm to 3.3 mm
D band 110 to 170 GHz 1.8 mm to 2.7 mm
Let us now take a look at the properties of Microwaves.
Properties of Microwaves
Following are the main properties of Microwaves.
Microwaves are the waves that radiate electromagnetic energy with shorter wavelength.
Microwaves are not reflected by Ionosphere.
Microwaves travel in a straight line and are reflected by the conducting surfaces.
Microwaves are easily attenuated within shorter distances.
Microwave currents can flow through a thin layer of a cable.
Advantages of Microwaves
There are many advantages of Microwaves such as the following −
Supports larger bandwidth and hence more information is transmitted. For this reason,
microwaves are used for point-to-point communications.
More antenna gain is possible.
Higher data rates are transmitted as the bandwidth is more.
Antenna size gets reduced, as the frequencies are higher.
Low power consumption as the signals are of higher frequencies.
Effect of fading gets reduced by using line of sight propagation.
Provides effective reflection area in the radar systems.
Satellite and terrestrial communications with high capacities are possible.
Low-cost miniature microwave components can be developed.
Effective spectrum usage with wide variety of applications in all available frequency
ranges of operation.
Disadvantages of Microwaves
There are a few disadvantages of Microwaves such as the following −
Cost of equipment or installation cost is high.
They are hefty and occupy more space.
Electromagnetic interference may occur.
Variations in dielectric properties with temperatures may occur.
Inherent inefficiency of electric power.
Applications of Microwaves
There are a wide variety of applications for Microwaves, which are not possible for other
radiations. They are −
Wireless Communications
For long distance telephone calls
Bluetooth
WIMAX operations
Outdoor broadcasting transmissions
Broadcast auxiliary services
Remote pickup unit
Studio/transmitter link
Direct Broadcast Satellite (DBS)
Personal Communication Systems (PCSs)
Wireless Local Area Networks (WLANs)
Cellular Video (CV) systems
Automobile collision avoidance system
Electronics
Fast jitter-free switches
Phase shifters
HF generation
Tuning elements
ECM/ECCM (Electronic Counter Measure) systems
Spread spectrum systems
Commercial Uses
Burglar alarms
Garage door openers
Police speed detectors
Identification by non-contact methods
Cell phones, pagers, wireless LANs
Satellite television, XM radio
Motion detectors
Remote sensing
Navigation
Global navigation satellite systems
Global Positioning System (GPS)
Military and Radar
Radars to detect the range and speed of the target.
SONAR applications
Air traffic control
Weather forecasting
Navigation of ships
Minesweeping applications
Speed limit enforcement
Military uses microwave frequencies for communications and for the above mentioned
applications.
Research Applications
Atomic resonances
Nuclear resonances
Radio Astronomy
Mark cosmic microwave background radiation
Detection of powerful waves in the universe
Detection of many radiations in the universe and earth’s atmosphere
Food Industry
Microwave ovens used for reheating and cooking
Food processing applications
Pre-heating applications
Pre-cooking
Roasting food grains/beans
Drying potato chips
Moisture levelling
Absorbing water molecules
Industrial Uses
Vulcanizing rubber
Analytical chemistry applications
Drying and reaction processes
Processing ceramics
Polymer matrix
Surface modification
Chemical vapor processing
Powder processing
Sterilizing pharmaceuticals
Chemical synthesis
Waste remediation
Power transmission
Tunnel boring
Breaking rock/concrete
Breaking up coal seams
Curing of cement
RF Lighting
Fusion reactors
Active denial systems
Semiconductor Processing Techniques
Reactive ion etching
Chemical vapor deposition
Spectroscopy
Electron Paramagnetic Resonance (EPR or ESR) Spectroscopy
To know about unpaired electrons in chemicals
To know the free radicals in materials
Electron chemistry
Medical Applications
Monitoring heartbeat
Lung water detection
Tumor detection
Regional hyperthermia
Therapeutic applications
Local heating
Angioplasty
Microwave tomography
Microwave Acoustic imaging
ELECTROMAGNETIC WAVES PRINCIPLES
Radio signals exist as a form of electromagnetic wave. This is the same form of radiation as light,
ultra-violet, infra-red, etc., differing only in the wavelength or frequency of the radiation.
Electromagnetic radiation can travel through many forms of medium. Air and free space form ideal
media. However conductive media like metals form a barrier through which they do not travel.
There are also some media through which they can travel but are attenuated.
Electromagnetic waves – e/m radiation basics
Electromagnetic waves or e/m radiation has two constituents. The radiation is made from electric
and magnetic components that are inseparable. The planes of the fields are at right angles to each
other and to the direction in which the wave is travelling.
An electromagnetic wave
It is useful to see where the different elements of the wave emanate from to gain a more complete
understanding of electromagnetic waves. The electric component of the wave results from the
voltage changes that occur as the antenna element is excited by the alternating waveform. The
lines of force in the electric field run along the same axis as the antenna, but spreading out as they
move away from it. This electric field is measured in terms of the change of potential over a given
distance, e.g. volts per metre, and this is known as the field strength. This measure is often used in
measuring the intensity of an electromagnetic wave at a particular point. The other component,
namely the magnetic field is at right angles to the electric field and hence it is at right angles to the
plane of the antenna. It is generated as a result of the current flow in the antenna.
Like other forms of electromagnetic wave, radio signals can be reflected, refracted and undergo
diffraction. In fact some of the first experiments with radio waves proved these facts, and they
were used to establish a link between radio waves and light rays.
Electromagnetic wave wavelength, frequency & velocity
There are a number of basic properties of electromagnetic waves, or any repetitive waves for that
matter that are particularly important.
Frequency, wavelength and speed are three key parameters for any electromagnetic wave.
E/m wave speed: Radio waves travel at the same speed as light. For most practical purposes the
speed is taken to be 300 000 000 metres per second although a more exact value is 299 792 500
metres per second. Although exceedingly fast, they still take a finite time to travel over a given
distance. With modern radio techniques, the time for a signal to propagate over a certain distance
needs to be taken into account. Radar for example uses the fact that signals take a certain time to
travel to determine the distance of a target. Other applications such as mobile phones also need to
take account of the time taken for signals to travel to ensure that the critical timings in the system
are not disrupted and that signals do not overlap.
E/m wave wavelength: This is the distance between a given point on one cycle and the same point
on the next cycle as shown. The easiest points to choose are the peaks as these are the easiest to
locate. The wavelength was used in the early days of radio or wireless to determine the position of
a signal on the dial of a set. Although it is not used for this purpose today, it is nevertheless an
important feature of any radio signal or for that matter any electromagnetic wave. The position of
a signal on the dial of a radio set or its position within the radio spectrum is now determined by its
frequency as this provides a more accurate and convenient method for determining the properties
of the signal.
Frequency: This is the number of times a particular point on the wave moves up and down in a
given time (normally a second). The unit of frequency is the Hertz and it is equal to one cycle per
second. This unit is named after the German scientist who discovered radio waves. The frequencies
used in radio are usually very high. Accordingly the prefixes kilo, Mega, and Giga are often seen.
1 kHz is 1000 Hz, 1 MHz is a million Hertz, and 1 GHz is a thousand million Hertz i.e. 1000 MHz.
Originally the unit of frequency was not given a name and cycles per second (c/s) were used. Some
older books may show these units together with their prefixes: kc/s; Mc/s etc. for higher
frequencies.
Frequency to Wavelength Conversion
Although wavelength was used as a measure for signals, frequencies are used exclusively today.
It is very easy to relate the frequency and wavelength as they are linked by the speed of light as
shown:
λ = cf
Where
λ = the wavelength in metres
f = frequency in Hertz
c = speed of radio waves (light) taken as 300 000 000 meters per second for all practical
purposes.
Electromagnetic waves are the key to radio and wireless communications. The fact that they can
travel over vast distances as well as being reflected, refracted and diffracted means that they have
been used for many years as the basis for radio communications over all distances from a few
centimeters to many hundreds of thousands or millions of miles.
MAXWELL ELECTROMAGNETIC EQUATIONS
Introduction
In 1864, James Clerk Maxwell (1831-1879) took all of the then known equations
of electricity and magnetism, and with the addition of a new term to one of the
equations, combined them into only four equations that could be used to derive all
the results of electromagnetic theory. These four equations came to be known as
Maxwell’s equations. The four Maxwell’s equations are (1) Gauss’s law for
electricity, (2) Gauss’s law for magnetism, (3) Ampere’s law with the addition of a
new term called the displacement current, and (4) Faraday’s law of electromagnetic
induction. With these four equations, Maxwell predicted that waves should exist in
the electromagnetic field. Thirteen years later, in 1887, Heinrich Hertz (1857-1894)
produced and detected these electromagnetic waves. Maxwell also predicted that
the speed of these electromagnetic waves should be 3 108 m/s. Observing that
this is also the speed of light, Maxwell declared that light itself is an electromagnetic
wave. In fact it eventually became known that there was an entire spectrum of these
electromagnetic waves. They differed only in frequency and wavelength. Finally,
it was found that these electromagnetic waves are capable of transmitting energy
from one place to another, even through the vacuum of space.
The Displacement Current and Ampere’s Law
In the study of a capacitor in chapter 23 (where we assumed that the current was
conventional current, that is a flow of positive charges) we saw that when the switch
in the circuit is closed, charge flows from the positive terminal of the battery to one
plate of the capacitor, called the positive plate, and charge also flows from the
negative plate of the capacitor back to the negative terminal of the battery. This is
shown in figure 29.1(a). Until the plates are completely charged, there is a current
into the positive plate, and a current out of the negative plate, yet there seems to be
no current between the plates. There is thus a discontinuity in the current in the
circuit because of the capacitor.
Maxwell electromagnetic equations. It includes Ampere's law, Faraday's law and Gauss's law.
Maxwell Equation 1. Ampere's law: As mentioned above, change in electric field(E) produces
magnetic field(H).
Maxwell Equation 2. Faraday's law of induction: As mentioned, change in magnetic field produces
electric field.
Maxwell Equation 3. Gauss's law for electric field: As mentioned above, electric charge can be
either sink or source of electric fields.
Maxwell Equation 4. Gauss's law for Magnetic field: As mentioned, working around the loop is
zero, i.e. divergence of magnetic flux density (B) is equal to zero.