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.