WIRELESS COMMUNICATION USING LPDA ANTENNA

ADITYA.SATTID.KUSHAL REDDY

E.DILIP ROY

Department of Electronics and Communication Engineering

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad – 500 075

2010

WIRELESS COMMUNICATION USING LPDA ANTENNA

PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

BY

ADITYA.SATTI (06261A0402) D.KUSHAL REDDY (06261A0415)

E.DILIP ROY (06261A0417)

Department of Electronics and Communication Engineering

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad – 500 075

2010

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad-500 075

Department of Electronics and Communication Engineering

CERTIFICATE

Date: 7th May 2010

This is to certify that the project work entitled

“Wireless Communication using LPDA Antenna”

is a bonafide work carried out by

ADITYA.SATTI (06261A0402)D.KUSHAL REDDY (06261A0415)

E.DILIP ROY (06261A0417)

in partial fulfillment of the requirements for the degree of BACHELOR OF

TECHNOLOGY in ELECTRONICS & COMMUNICATION

ENGINEERING by the Jawaharlal Nehru Technological University, Hyderabad

during the academic year 2009-10.

The results embodied in this report have not been submitted to any other

University or Institution for the award of any degree or diploma.

-------------------------- -------------------------- Mrs.D.Rajeshwari Devi Assistant professor Dr. E.NagabhooshanamFaculty Advisor/Liaison Professor & Head

(i)

ACKNOWLEDGEMENT

We are highly indebted to our Faculty Liaison Mrs.D.Rajeshwari Devi,

Electronics and Communication Engineering Department, who has given us all the

necessary technical guidance in carrying out this Project.

We wish to express our sincere thanks to Dr. E. Nagabhooshanam, Head of the

Department of Electronics and Communication Engineering, M.G.I.T., for permitting us

to pursue our Project and encouraging us throughout the Project.

Finally, we thank all the people who have directly or indirectly help us through

the course of our Project.

We express our deep sense of gratitude to our Guide K.V.Shruti., Hyderabad, for

his valuable guidance and encouragement in carrying out our Project.

ADITYA.SATTI D.KUSHAL REDDY

E.DILIP ROY

(iii)

ABSTRACT

Wireless communication was a revolution over the process of communication

using wires.Wireless communication is the transfer of information over a distance

without the use of enhanced electrical conductors or "wires". The distances involved may

be short a few meters as in television remote control or long thousands or millions of

kilometers for radio communications. When the context is clear, the term is often

shortened to "wireless". Wireless communication is generally considered to be a branch

of telecommunications. It encompasses various types of fixed, mobile, and portable two-

way radios, cellular telephones, personal digital assistants (PDAs), and wireless

networking. Other examples of wireless technology include GPS units, garage door

openers and or garage doors, wireless computer mice, keyboards and headsets, satellite

television and cordless telephones.

In our project we apply wireless communication using a LPDA antenna , log

periodic dipole array antenna . It is a log-periodic antenna (LP, also known as a log-

periodic array) is a broadband, multielement, unidirectional, narrow-beam antenna that

has impedance and radiation characteristics that are regularly repetitive as a logarithmic

function of the excitation frequency. The individual components are often dipoles, as in

a log-periodic dipole array (LPDA). Log-periodic antennas are designed to be self-

similar and are thus also fractal antenna arrays. It is normal to drive alternating elements

with 180° (π radians) of phase shift from one another. This is normally done by

connecting individual elements to alternating wires of a balanced transmission line. The

length and spacing of the elements of a log-periodic antenna increase logarithmically

from one end to the other. A plot of the input impedance as a function of logarithm of the

excitation frequency shows a periodic variation.

This antenna design is used where a wide range of frequencies is needed while still

having moderate gain and directionality. It is sometimes used for a

(VHF/UHF) television antenna.

(iv)

LIST OF FIGURES

1.2 Frequency Spectrum

6

2.2:Critical Angle 10

2.3:Radiation Pattern 15

4.5 Block Diagram For VSWR Measurement 22

4.6 Beam Width and Front To Back Ratio Measurement Setup23

4.8 Gain Measurement Setup 24

5.1 Block Diagram Description

25

5.1.1 Condenser Microphone 28

5.1.2 IC LA4510 29 5.1.3 Oscillator 30 5.1.3 RF Oscillators 32

5.1.4 Amplitude Modulation 34

5.2 Regulated Power Supply 41

5.2.1 Transformer 42

5.2.3 Half Wave Rectifier 44

5.2.3(a) RC-Low Pass Filter 46

5.2.3(b) RC-High Pass Filter 47

5.3.1 LC Oscillator 50

(v)5.3.3 AM Diode Detector 52

5.3.5 Speaker 54

6.2 LPDA Antenna 57

6.3 Radiation Pattern 65

7.1 Network Analyzer 67

7.2 . Directional coupler circuit configurations 69

(vi)

TABLE OF CONTENTS

CERTIFICATE FROM ECE DEPARTMENT (i)

ACKNOWLEDGEMENTS (iii)

ABSTRACT (iv)

LIST OF FIGURES (v)

CHAPTER :1.INTRODUCTION 1

1.1 AIM OF THE PROJECT 2

1.2 METHODOLOGY 2

1.3 SIGNIFICANCE AND APPLICATIONS 2

1.4 OVERVIEW 2

1.5 WIRELESS COMMUNICATION 3

1.6 ELECTROMAGNETIC SPECTRUM 5

CHAPTER :2.ANTENNA 8

2.1 FIELD INTENSITY 8

2.2 WAVE ATTENUATION 8

2.2.1 GROUND WAVE PROPAGATION 9

2.2.2 SKY WAVE PROPAGATION 9

2.2.3 SPACE WAVE PROPAGATION 11

2.4 SPECIFICATION OF AN ANTENNA 12

2.4.1 FREQUENCY RANGE 12

2.4.2 BANDWIDTH 12

2.4.3 VOLTAGE STANDING WAVE RATIO 13

2.4.4 GAIN AND DIRECTIVITY 14

2.4.5 RADIATION PATTERN 15

2.4.6 BEAM WIDTH AND GAIN OF MAIN LOBE 16

2.4.7 POLARISATION 17

2.4.8 FRONT TO BACK RATIO 17

CHAPTER :3 TYPES OF ANTENNA 18

3.1 MF ANTENNA 18

3.2 HF ANTENNA 18

3.3 VHF ANTENNA 19

3.4 UHF ANTENNA 19

CHAPTER:4 ANTENNA TESTING PROCEDURE 20

4.1 VOLTAGE STANDING WAVE RATIO 20

4.2 VOLTAGE STANDING WAVE RATIO MEASUREMENT 20

4.3 FINDING APROPER LOCATION TO TEST ANTENNA 20

4.4 TEST THE ANTENNA 21

4.5 BANDWIDTH 22

4.6 BEANWIDTH 22

4.7 FRONT TO BACK RATIO 23

4.8 GAIN MEASUREMENT 24

CHAPTER :5 BLOCK DIAGRAM DESCRIPTION 25

5.1 TRANSMITTER 25

5.1.1 MICROPHONE 27

5.1.2 AUDIO AMPLIFIER 28

5.1.3 OSCILLATOR 30

5.1.4 AMPLITUDE MODULATION 33

5.1.5 MIXERS 35

5.1.6 POWER AMPLIFIERS 36

5.2 REGULATED POWER SUPPLY 41

5.2.1 TRANSFORMERS 42

5.2.2 RECTIFIERS 43

5.2.3 FILTER CIRCUITS 46

5.3 RECIEVERS 47

5.3.1 TUNED CIRCUITS 47

5.3.2 DETECTORS 51

5.3.3 AMPLIFIER DEMODULATOR 52

5.3.4 AUDIO AMPLIFIER 53

5.3.5 SPEAKER 53

CHAPTER:6 LOG PERIODIC DIPOLE ARRAY 56

6.1 INTRODUCTION 56

6.2 DESIGN AND CONSTRUCTION OF LPDA 57

6.3 DESIGN PROCEDURE 63

CHAPTER :7 LPDA ANTENNA TESTING 67

7.1 NETWORK ANALZER 67

7.2 DIRECTIONAL COUPLER 69

7.3 VOLTAGE STANDING WAVE ROTIO 69

7.4 OPERATING BANDWIDTH 71

7.5 OPERATING WAVELENGTH 71

7.6 APEX ANGLE 71

7.7 LENGTH OF ANTENNA 71

7.8 DISTANCE BETWEEN TWO ELEMENTS 72

7.9 CONCLUSION 72

REFERENCES 74

CHAPTER :1

INTRODUCTION

1.1 Aim of the project:

The main objective of this project is to develop an effective wireless

communication module using LPDA antenna which has a effective gain.

1.2 Methodology:

The process of wireless communication is employed over here using a transmitter

section and a receiver section which have LPDA antennas on each side which are lined in

a matter of line of sight communication.

1.3 Significance and applications:

Automatic door opening systems using IR sensors plays a very important role in domestic

applications. The elimination of manual supervision adds up as an additional advantage

for its usage. Its significance can be proved by considering the following specialties of kit

designed by us

Reliability: Reliability is one such factor that every communication

system should have in order to render its services without malfunctioning

over along period of time. We have designed a LPDA antenna which is

itself very reliable and also operates very efficiently under normal

condition

Cost: The design is implemented at an economical price.

1.4 Organization of the report:

The report totally consists of seven chapters - Chapter 1 gives the introduction to the

project, Chapter 2 provides an overview of the antenna, Chapter 3 specifies the types of

antennas, Chapter 4 explains the antenna testing procedure, Chapter 5 explains in detail

about the block diagram, chapter 6 provides description of log periodic dipole array

antenna, chapter 7 describes the LPDA antenna testing procedure, and then followed by

the conclusion.

1.5 WIRELESS COMMUNICATION

Wireless communication is the transfer of information over a distance without the use of

enhanced electrical conductors or "wires".The distances involved may be short (a few

meters as in television remote control) or long (thousands or millions of kilometers for

radio communications). When the context is clear, the term is often shortened to

"wireless". Wireless communication is generally considered to be a branch of

telecommunications.

It encompasses various types of fixed, mobile, and portable two-way radios,

cellular telephones, personal digital assistants (PDAs), and wireless networking. Other

examples of wireless technology include GPS units, garage door openers and or garage

doors, wireless computer mice, keyboards and headsets, satellite television and cordless

telephones

The world's first wireless telephone conversation occurred in 1880, when

Alexander Graham Bell and Charles Sumner Tainter invented and patented the

photophone, a telephone that conducted audio conversations wirelessly over modulated

light beams (which are narrow projections of electromagnetic waves). In that distant era

when utilities did not yet exist to provide electricity, and lasers had not even been

conceived of in science fiction, there were no practical applications for their invention,

which was highly limited by the availability of both sunlight and good weather. Similar

to free space optical communication, the photophone also required a clear line of sight

between its transmitter and its receiver. It would be several decades before the

photophone's principles found their first practical applications in military

communications and later in fiber-optic communications.

The term "wireless" came into public use to refer to a radio receiver or transceiver

(a dual purpose receiver and transmitter device), establishing its usage in the field of

wireless telegraphy early on; now the term is used to describe modern wireless

connections such as in cellular networks and wireless broadband Internet. It is also used

in a general sense to refer to any type of operation that is implemented without the use of

wires, such as "wireless remote control" or "wireless energy transfer", regardless of the

specific technology (e.g. radio, infrared, ultrasonic) that is used to accomplish the

operation. While Guglielmo Marconi and Karl Ferdinand Braun were awarded the 1909

Nobel Prize for Physics for their contribution to wireless telegraphy, it has only been of

recent years that Nikola Tesla has been formally recognized as the true father and

inventor of radio.

Handheld wireless radios such as this Maritime VHF radio transceiver use

electromagnetic waves to implement a form of wireless communications technology.

Wireless operations permits services, such as long range communications, that are

impossible or impractical to implement with the use of wires. The term is commonly used

in the telecommunications industry to refer to telecommunications systems (e.g. radio

transmitters and receivers, remote controls, computer networks, network terminals, etc.)

which use some form of energy (e.g. radio frequency (RF), infrared light, laser light,

visible light, acoustic energy, etc.) to transfer information without the use of wires. [2]

Information is transferred in this manner over both short and long distances.

1.6 ELECTRO MAGNETIC SPECTRUM

The electromagnetic spectrum is a vast band of energy frequencies extending from radio

waves to gamma waves, from the very lowest frequencies to the highest possible

frequencies.

The spectrum is arranged by the frequency of its waves, from the longest, lowest energy

waves to the shortest, highest energy waves.

Our ability to tune in the more exotic electromagnetic waves has grown in recent

decades. For instance, radio is part of the spectrum, and it was only in the 20th Century

that humans began to be able to use any of the electromagnetic spectrum, starting with

radio at the long-wave end of the spectrum.

Today, living and working in the 21st century, we make great use of the electromagnetic

spectrum in all of our vocations and avocations. All of the frequencies we use for

transmitting and receiving energy are part of the electromagnetic spectrum. For instance:

RADIO. We use the radio portion of the electromagnetic spectrum for

many things, including television and radio broadcasting, telephones and

other wireless communications, navigation and radar for a variety of

measurements including police speed traps, and even microwave cooking

ovens.

Our AM broadcast stations transmit signals in what is referred to as the

medium-wave portion of the spectrum. FM music stations use very high

frequency (VHF) transmitters. Television stations use the VHF and ultra

high frequency (UHF) regions of the spectrum.

INFRARED LIGHT. Infrared light is on the spectrum at frequencies

above radio and just below the range of human vision. Infrared light is

heat. Three-quarters of the radiation emitted by a light-bulb is IR. We use

infrared transmitters to remotely control our TV sets. We can record

infrared light on photographic film and we have equipment that can see

hot bodies in deep space in the infrared light they send out.

VISIBLE LIGHT. Visible light, which we receive with our eyes, is along

the spectrum between infrared and ultraviolet light, which we can't see. Of

course, we can collect visible light with photographic film.

Our eyes can detect only a tiny part of the electromagnetic spectrum,

called visible light. This means that there's a great deal happening

around us that we're simply not aware of, unless we have instruments

to detect it.

Light waves are given off by anything that's hot enough to glow.

This is how light bulbs work - an electric current heats the lamp

filament to around 3,000 degrees, and it glows white-hot.

The surface of the Sun is around 5,600 degrees, and it gives off a

great deal of light.

White light is actually made up of a whole range of colours, mixed

together.

We can see this if we pass white light through a glass prism - the

violet light is bent ("refracted") more than the red, because it has a

shorter wavelength - and we see a rainbow of colours.

This is called 'dispersion', and allows us to work out what stars are

made of by looking at the mixture of wavelengths in the light

ULTRAVIOLET LIGHT. On the spectrum, ultraviolet light is above

visible light. UV is dangerous to living organisms. So, it is used to sterilize

medical instruments by killing bacteria and viruses. We have photographic

film that can capture ultraviolet light. Ten percent of the energy radiated

by our star, the Sun, is ultraviolet light.

X-RAYS. Farther along the spectrum are X-rays. Their invisible energy is

produced when gas is heated to millions of degrees. X-ray energy is

absorbed by matter it penetrates depending upon the atomic weight of that

matter. Because X-rays can change a photographic emulsion just as visible

light does, we use them to take pictures of the insides of people and things.

GAMMA RAYS: Gamma rays are beyond X-rays on the electromagnetic spectrum.

Gamma rays that we find arriving at Earth from deep space are the result of violent

cosmic events such as supernovas, other nuclear explosions, and radioactive decay

30

km

|

3

km

|

300

m

|

30

m

|

3

m

|

30

cm

|

3

cm

|

3

mm

|

VLF LF MF HF VHF UHF SHF EHF InfraredVisible

Light

|

10

kHz

|

100

kHz

|

1

MHz

|

10

MHz

|

100

MHz

|

1

GHz

|

10

GHz

|

100

GHz

Fig: 1.6 Frequency spectrum

Table 1.6: Frequency Band

Frequency Band

10 kHz to 30 kHz Very Low Frequency (VLF)

30 kHz to 300 kHz Low Frequency (LF)

300 kHz to 3 MHz Medium Frequency (MF)

3 MHz to 30 MHz High Frequency (HF)

30 MHz to 144 MHz

144 MHz to 174 MHz

174 MHz to 328.6 MHzVery High Frequency (VHF)

328.6 MHz to 450 MHz

450 MHz to 470 MHz

470 MHz to 806 MHz

806 MHz to 960 MHz

960 MHz to 2.3 GHz

2.3 GHz to 2.9 GHz

Ultra High Frequency (UHF)

2.9 GHz to 30 GHzSuper High Frequency (SHF)

30 GHz and above Extremely High Frequency (EHF)

CHAPTER: 2

ANTENNA

Antennas are electric circuits of a special kind. In the ordinary circuits, the

dimensions of coils, capacitors and connections usually are small compared with the

wavelength that corresponds to the frequency in use. When this is the case, most of the

electromagnetic energy stays in the circuit itself and is either used up in performing

useful work or is converted in to heat. But when the dimensions of wiring or components

become appreciable, compared to the wavelength, some of the energy escapes by

radiation in the form of electromagnetic waves. When the circuit is intentionally

designed so that the major portion of the energy is radiated, such circuit is an

ANTENNA.

The purpose of any antenna is to convert radio frequency electric current to

electromagnetic waves, which are then radiated in to the space and vice versa. An

Antenna can transmit as well as receive signals.

2.1 Field Intensity

In free space the field intensity of the wave varies inversely with the distance of

source, once you are in radiating far field of the antenna. The energy from the propagated

wave decreases with distance from the source. This decrease in strength is caused by

spreading of the wave energy over ever-larger spheres as the distance from the source

increases.

2.2 Wave Attenuation

In free space the field intensity of the wave varies inversely

with the distance of source, once you are in radiating far field of the

antenna. For example if in field strength at 1 mile from the source is

100 milli volts per meter, it will be 50 milli volts per meter at 2 miles

and so on. The relationship between field intensity and power density

is similar to that for voltage and power in ordinary circuits. In practice

attenuation of the wave energy may be much greater than the inverse

distance. The wave does not travel in a vacuum and the receiving

antenna seldom is situated so there is a clear line of sight. The Earth is

spherical and the waves do not penetrate its surface appreciably, so

communication beyond visual distance must be by some means that

will bend the waves around the curvature of Earth.

The radio communication is carried on by means of electromagnetic waves through

the Earth’s atmosphere. It is important to understand the nature of these waves and their

behavior in the propagation medium. Most of the antennas will radiate the power or

receive the signals efficiently but no antenna will do all the things equally, well under all

circumstances. It is necessary that one needs to know how about the propagation for best

results.

2.2.1GROUND WAVE PROPAGATION

Depending upon the wave length, radio wave may be

reflected by buildings, trees, vehicles, the ground, water ionized layers

in the upper atmosphere. The radio waves are affected in many ways

by the media through which they travel. The ground wave could be

traveling in actual contact with the ground where it is called “surface

wave”. It could travel directly between transmitting and receiving

antennas, when they are high enough, so they can see each other.

This is commonly called “direct wave”. The ground wave also travels

between the transmitting and receiving antennas by reflections or

diffractions off intervening terrain between them. The ground

influenced wave may interact with direct wave to create a vector

summed resultant at the receive antenna.

2.2.2 SKY WAVE PROPAGATION

All HF antennas propagate in sky wave propagation.

The ground wave is commonly applied to propagation that is confined to lower

atmosphere. The atmosphere is a region where the air pressure is so low, that free

electrons and ions can move about for some time without getting close enough to

recombine in to neutral atoms. The lowest known ionized region called “D Layer” lies

between 60 to 92km above Earth. In this relatively low and dense part of the atmosphere,

where the ionization level is directly related to sunlight. It begins at sunrise, peaks at local

noon, and disappears as sunsets.

The frequencies between 1.5 to 4Meters having the

longest wavelength suffer the highest daytime absorption loss. They

go dead quickly in the morning but become alive in late afternoon.

This effect is less at 7MHz. or 14MHz. The ‘D’ Layer is ineffective in

bending HF Waves back to Earth and not useful in long distance

communication. During daytime 7MHz. and above are used for short

distance communication either transmit or receive.

The portion of ionosphere useful for long distance

communication is ‘E’ Layer about 100km to 115km above the Earth. In

the ‘E’ Layer the density and ionization reaches max at midday and

drops quickly after sun down. The minimum is at midnight. Most of

the long distance communication capacity stems from the tenuous

outer reaches of the Earth’s atmosphere is called ‘F’ “Layer”, situated

at 160kms to 500kms from Earth, during day and also this region has

its ability to reflect wave back to Earth even in night depending on the

season of the year, the latitudes, time of day.

Fig2.2:Critical Angle

Critical Angle

As seen above the antenna design for long distance

communication, the first three waves will do no good, they all take off

at angles high enough that they pass through the ionosphere layers

and are lost in the space. As the angle of radiation decreases the

amount of reflection or bending needed for sky wave communication

also decreases. The fourth wave from the left takes off at what is

called “critical angle”, the highest that will return the wave to Earth, at

a given density of ionization in the layer for the frequency under

consideration at a point ‘A’.

Hopping

If the antenna that radiates at a lower angle, as with 5th

wave from the left. This wave gets reflected to Earth far away than the

4th wave at point B similarly 6th wave with its low radiation angle comes

back to Earth much farther away from point ‘B’ and so on. The Earth

itself acts as a reflector of radio waves. Often radio signals are re-

reflected from Earth at point ‘A’. This signal reflected from point ‘A’

travels through the ionosphere again to point ‘B’ Signal travel from

Earth through the ionosphere and back to the Earth is called ‘hop’.

Skip distance

When the critical angle is less than 90° there will always be a

region around the transmitter where the ionospherically propagated

signal cannot be heard or heard weakly. This area lies between the

outer limit of his ground wave range and the inner edge of energy

return from the Ionosphere. It is called “Skip Zone” or Null Zone and

the distance between the originating site and the beginning of the

ionosphere return is called “Skip Distance”.

Fading

When all the variable factors in long distance communication

are taken into account it is not surprising that signals vary in strength

during almost every contact beyond the local range, which is called

fading. These are mainly the result of changes in the temperatures

and moisture content of the air in the 1st few thousand feet above the

ground on the paths covered by ionospheric modes, the causes of

fading are very complex – constantly changing layer height and

density, random polarization shift, portions of the signal arriving out of

phase and so on.

Some immunity from fading during reception can be had by

using two or more receivers connected to separate antennas,

preferably with different polarizations and combining the receiver

outputs in what is known as “diversity receiving system”.

Reception

The strength of the signal will depend on the transmitter

power. If the far off signals are to be received, it is possible only with

high power transmitter on the other end. If the receiving antenna falls

in a skip zone, there will be no signal. Hence it is necessary to select

frequencies for reception in the full band, depending on the day

frequencies, night frequencies and also the season.

a) SPACE WAVE PROPAGATION

Space wave propagation is otherwise called as LINE OF SIGHT

COMMUNICATION. In which the transmitting antenna should see the receiving

antenna.

All VHF, UHF and Microwave frequencies antennas propagate in space wave

propagation

b) SPECIFICATIONS OF AN ANTENNA

2.4.1 Frequency Range

The frequency range of antenna is very important to calculate its wave length,

based on which an antenna can be designed. The range of frequency in which antenna

either radiates or receives signal by satisfying all other specifications is called as

frequency range.

The Frequency ranges are divided into:

1. Medium Frequencies (MF) : 300 KHZ to 3 MHZ.

2. High Frequencies(HF) : 3 MHZ to 30 MHz

3. Very High Frequencies(VHF) : 30 MHZ to 300 MHz

4. Ultra High Frequencies(UHF) : 300 MHZ to 1 GHZ

5. Microwave Frequencies : 1 GHZ and above

Calculation of a wave length:

For example if the Frequency range of an antenna is 300 MHz to 350 MHz then

its wave length is

= Speed of the electromagnetic wave

Mid frequency of the frequency range

Speed of the electromagnetic wave = Speed of the light = C = 3 x108 m/sec

Mid Frequency= Lower frequency + Higher frequency = 300+350 =650= 325 MHz

2 2 2

= 3 x10 8 m/sec = 300 m = 0.9 m

325 MHZ 325

By using the value of we design the antennas for /2 or /4.

2.4.2 Bandwidth

The bandwidth of an antenna is a measure of its ability to radiate or receive

different frequencies. It refers to the frequency range over which operation is satisfactory

and is generally taken between the half power points in the direction of maximum

radiation. The bandwidth is the range of frequencies that the antenna can receive (or

radiate) with a power efficiency of 50% (0.5) or more or a voltage efficiency of 70.7%

(that is –3dB points). The operating frequency range is specified by quoting the upper

and lower frequencies but the bandwidth is often quoted as a relative value. Bandwidth is

commonly expressed in one of the two ways:

1. Percentage.

2. As a function or multiple of an octave.

An octave is a band of frequencies between one frequency can the frequency that is

double or half the first frequency, for instance, we have an octave between 300 MHz. and

600 MHz.). When it is expressed as a percentage bandwidth its center frequency should

be quoted and the percentage expressed in octaves its lower and upper frequency should

be also quoted.

c) Voltage Standing Wave Ratio(VSWR)

If a lossless transmission line has infinite length or terminated in the characteristic

impedance, all the power applied to the line by transmitter at one end is absorbed by the

load (antenna at the other) end. Conversely if a finite piece of line is terminated in an

impedance not equal to the characteristic impedance, only some power is absorbed in the

load and remaining power is reflected

The single cycle of a signal is launched down a transmission line

which is called the ‘incidence’ or forward wave. When it reached the

end of the transmission line if it is not totally absorbed by the antenna

then it (a part of it) will be reflected back towards the transmitter. The

incident and reflected waves are both called traveling waves. The

reflected wave represents the power that is lost and will interfere with

incident waves the resultant caused is called standing wave.

The ratio of the maximum voltage along the feeder line to the

minimum voltage, i.e. Emax to Emin is defined as voltage standing

wave ratio (VSWR)

VSWR =

1: 1 is the VSWR for an ideal antenna but practically 1:1

VSWR cannot be obtained, up to 2:1 is tolerated.

Similarly the ratio of maximum current to the minimum current is same as

VSWR. Either of the measurements will determine the standing wave ratio, which is

index of the mismatch existing between the transmitter and antenna, through transmission

lines.

Every Antenna used for Transmission or Reception should be properly

matched to the Trans receiver to ensure that maximum power is radiated or received for

efficient Communication. For example if a transmitter is designed to deliver 100 Watts

of RF Power output, the entire Power is to be transmitted fully but due to line losses, only

80 to 90% is transmitted. Hence the antenna efficiency is to be measured before it is

connected to the equipment, which test is otherwise called VSWR Test.

2.4.4 Gain and Directivity

d) All antennas, even simplest types, exhibits directive effects in the intensity of

radiation is not all the same in all directions from the antenna. This property

of radiating more strongly in some directions than in others is called

directivity of antenna. The ratio of the maximum power density, to the

average power density taken over the entire sphere is the directivity of the

antenna.

D =

Where

D = Directivity

P = Power density at its max. point

E

max

P

Pav

Pav = average power density

e) Gain of the antenna is closely related to directivity, so the antenna gain is

= K Pav

Where

G = Gain expressed as power ratio

K = is the efficiency

The power gain of an antenna system is usually expressed in decibels for

convenience. The directive gain is defined in a particular direction is the ratio of the

power density radiated in that direction by that antenna to the power density that

would be radiated by the isotropic antenna.

© Decibel is an excellent practical unit for measuring power ratios. The number of

decibels corresponding to any power ratio is equal to 10 times the common logarithm of

the of the power ratio or dB= 10 log P1/P2

2.4.5 Radiation pattern

A graph showing the actual or relative field intensity at a fixed distance, as a function

of the direction on the Antenna system is called radiation pattern. To understand the

basis of such a graph, please see the figure. RF Power is fed to the antenna under test

and the receiver or detector, which is also called field strength meter, indicates the RF

Signal received. For convenience, the transmitting antenna under test is rotated slowly

to numerous positions. Different types of radiation patterns are appended herewith.

PG

Fig2.3:Radiation Pattern

The radiation of RF signal is the “beam” and the width of the beam differs from

different categories of Antennas.

The antenna is a reciprocal device, means it radiates or receives electro

magnetic energy in the same way. This although the radiation pattern is identified with

an antenna that is transmitting power, the same properties would apply to the antenna

even if it was receiving power. Any difference between the received and radiated powers

can be attributed to the difference between the feed networks and the equipment

associated with the receiver and transmitter. The antenna radiates the greatest amount of

power along its bore sight and also receives power most efficiently in this direction.

The radiation pattern of an antenna is peculiar to the type of a antenna

and its electrical characteristics as well as its physical dimension. It is measured at a

constant distance in the far field. The radiation pattern of an antenna is usually plotted in

terms of relative power. The power at bore sight that it at the position of maximum

radiated power is usually plotted at 00. Thus the power in all other positions appears as a

negative value. In other words the radiated power is normalized to the power at bore

sight. The main reason for using dB instead of linear power is that the power at the nulls

is often of the order of 10,000 times less than the power on the bore sight, which means

that the scales would have to be very large in order to cover the whole range of power

values.

The radiation pattern is usually measured in the two principal planes

namely, the azimuth and the elevation planes. The radiated / received dB is plotted

against the angle that is made with the bore sight direction. If the antenna is not

physically symmetrical about each of its principal planes then one can also expect its

radiation pattern in these planes to be unsymmetrical. The radiation pattern can be

plotted using the polar or the rectangular / certesian co-ordinates.

2.4.6 The beam width and gain of main lobe

The beam width of antenna is the angular separation between the two half-power

points on the power density radiation pattern. The beam width of an antenna is

commonly defined in two ways. The most well known definition is the –3dB or half

power beam width but the 10dB beam width is also used especially for antenna with very

narrow beams the –3dB or half power beam width of an antenna is taken as the width in

degrees at the points on either side of the main beam where the radiated level is 3dB

lower than the maximum lobe value. The –10dB value is taken as the width in degrees

on either side of the main beam where the radiated level is 10dB lower than the

maximum lobe value.

The IEEE definition of gain of an antenna relates to the power radiated by the

antenna to that radiated by an isotropic antenna (that radiates equally in all direction) and

is quoted as a linear ratio or in decibels referred to an isotropic (dBi, i : for isotropic)

when we say that the gain of an antenna is for instance, 20dBi (100 in linear terms) we

man that an isotropic antenna would have to radiate 100 times more power to give the

same intensity at the same distance as that particular directional antenna.

The radiation pattern of an antenna shows the power on the bore sight as 0dB and

the power in other directions as negative values. The gain in all directions is plotted

relative to the gain on bore sight. In order to find the absolute gain in any direction the

gain on bore sight must be known. If this gain is expressed in decibels, (as is normally

the case) then this value can simply be added to the gain at any point to give the absolute

gain. The absolute gain on bore sight is measured by comparison with a standard gain

antenna, which functions as a reference antenna whose gain is calculated or measured

with a high degree of accuracy.

2.4.7 Polarization

Polarization or plane of Polarization of a radio wave can be defined by the

direction in which the electrical vector is aligned during the passage of atleast one full

cycle. Polarization refers to the physical orientation of the radiated electro

magnetic waves in space.

Polarization is a characteristic of the antenna that they radiate linearly

(Vertical or horizontal) waves. The direction of an antenna and polarization is alike i.e., if

an antenna is vertical, it will radiates vertically polarized waves and a horizontal antenna,

horizontally polarized waves.

Beside linear polarization antenna may also radiate circularly or elliptical

polarized waves. If two linearly polarized waves are simultaneously produced in the same

direction from the same antenna provided that the two linear polarizations are mutually

perpendicular to each other with a phase difference of 90º, then circularly polarized

waves are produced. Circular polarization may be right handed or left handed depending

upon the sense of rotation i.e., phase difference is positive or negative.

2.4.8 Front to back ratio

The front to back ratio is a measure of the ability of a directional antenna to

concentrate the beam in the required forward direction. In linear terms, it is defined as

the ratio of the maximum power in the main beam (foresight) to that in the back lobe. It

is usually expressed in decibels as the difference between the level on foresight and at

180 degrees off foresight. It this difference is says 35dB then the front to back ratio of

the antenna is 35dB in linear terms it would mean that the level of the back lobe is 3, 162

times less than the level of the foresight.

CHAPTER:3

TYPES OF ANTENNAS

Antennas may be classified according to their frequency range of operation:

1. M.F. Antennas

2. H.F.Antennas

3. V.H.F.Antennas

4. U.H.F.Antennas

5. Microwave Antennas

3.1M.F. Antennas:

1. M.F. LOCATOR BEACON

M.F. BEACON AERIAL

‘T’ ANTENNA

3.2 H.F. Antennas:

1. H.F. MONOCONE ANTENNA

1. FOLDED DIPOLE ANTENNA

CONIFAN ANTENNA

H.F. BROAD BAND DIPOLE

SLOPY DIPOLE ANTENNA

1. HF VERTICAL DIPOLE

2. H.F. ANTENNA OMNI DIRECTIONAL

H.F. VERTICAL RADIATOR

H.F. LOG PERIODIC ANTENNA

H.F. RECEIVING SYSTEM (1.6 to 30 MHz.)

The system consists of one vertically polarised H.F. Omni Directional Antenna

covering a frequency range from 1.6 to 30 MHz. coupled with one H.F. Antenna

Multicoupler, Coupling 8 communication receivers simultaneously, each tuned to their

respective signal required for them.

3.3 V.H.F.Antennas:

GROUND PLANE ANTENNA

CAGE DIPOLE

DVOR MONITOR ANTENNA

HULA HOOP MOBILE ANTENNA

SLEEVE MONOPOLE ANTENNA

V.H.F. YAGI ANTENNA

YAGI WITH FOLDED DIPOLE

TELEMETRY ANTENNA

LOG PERIODIC ANTENNA

3.4U.H.F.Antennas:

HELICAL ANTENNA

BICONICAL ANTENNA

CORNER REFLECTOR ANTENNA

DISCONE ANTENNA

U H F COLLINEAR ANTENNA

VHF / UHF CAGE DIPOLE ANTENNA

MAGNETIC BASE ANTENNA

YAGI ANTENNA

MOBILE VEHICULAR JAMMER ANTENNA

WHIP ANTENNA( TYPE : AT/271A/PRC)

CHAPTER:4

ANTENNA TESTING PROCEDURE

4.1 VSWR

Voltage Standing Wave Ratio (VSWR) is the ratio of the maximum voltage to the

minimum voltage in the standing wave on a transmission line. Standing waves are the

result of reflected RF energy. As the VSWR approaches 1.00:1, the reflections on the line

approach zero and maximum power may be transmitted.

Reflections occur any place where the impedance of the transmission line

changes. Inside a typical base station antenna, the impedance of the line is changed at

many places in order to distribute the RF energy across the aperture. Antenna engineers

design matching sections inside the antenna to minimize the overall impedance change

(and associated reflections) relative to a 50 ohm reference. Measuring the VSWR of the

antenna indicates the how closely the antenna is matched to 50 ohms impedance and

indicates the magnitude of the reflected energy.

4.2 VSWR measurement

The VSWR of base station antennas is measured using a device called a

network analyzer. The network analyzer is a meter that injects signals into the antenna

across a wide frequency band and measures the magnitude of the reflected signals.

Calibration standards are used to “calibrate” or “zero” the network analyzer at the end of

a test cable. This point becomes the “reference plane” to which the impedance of the

antenna under test is compared.

4.3 Finding a proper location to test antennas

When measuring VSWR, a small amount of RF energy is transmitted by the network

analyzer and radiated from the antenna under test. Any external objects (particularly

metal objects) in the field of view of the antenna will reflect that energy back into the

antenna. This reflected signal will add to or subtract from the internal reflections of the

antenna as a function of wavelength, causing ripple to be seen in the VSWR

measurement. The magnitude of this ripple can be large enough to make a “good”

antenna appear “bad.”

When base station antennas are tested at the factory, the antenna is placed in front

of a wall of RF absorbing material. The RF absorber dissipates the radiated energy from

the antenna and prevents reflections outside of the antenna from bouncing back into the

measurement. This allows an accurate, repeatable measure of the antenna’s VSWR and

closely simulates the free-space environment the antenna will see in the field.

Since RF absorbing walls are not generally available in the field, care must be

taken to minimize external reflections when measuring the antenna. The best test location

is one that allows a clear, unobstructed view of the sky over a wide horizontal area. Since

most base station antennas have a wide beam in the azimuth direction, care must be given

to minimize obstructions ± 60° on either side of the antenna. Testing the antenna while it

is installed on a tower will typically provide good results. If the antenna is being tested on

the ground, candidate test locations are fields, empty lots, rooftops or loading docks.

Other considerations:

1) Never test base station antennas inside a building (unless you have a wall of RF

absorber!)

2) Do not point the antenna at the ground.

3) Avoid parked cars, fences and buildings within the field of view of the antenna.

4) Do not put any part of your body in front of the antenna while performing a test. Arms

and legs in front of the antenna will cause large reflections!

Calibrate the network analyzer + test cable according to the manufacturer’s

recommended procedure.

4.4 Test the antenna

Attach the calibrated reference plane (test cable) directly to the antenna under test.

Make sure the connection is tight. Observe the maximum VSWR in the frequency range

of interest on the network analyzer. Compare the value measured to the antenna

manufacturer’s specification for that antenna to determine if the antenna is “good” or

“bad.”

Do not measure the antenna VSWR through a feed line and/or jumper cable!

Measuring the antenna + feed line and/or jumper cable will provide a measure of the

cascaded mismatch of the various transmission line components. The VSWR measured in

this manner is not an accurate measure of the antenna mismatch by itself. To determine

whether or not the antenna is functioning correctly, the reference plane of the network

analyzer must be connected directly to the antenna under test.

Fig4.5:Block Diagram for VSWR Measurement

4.5 BANDWIDTH

The circuit is connected as above and measured the VSWR value of antenna for

different frequencies in between the band for which antenna is designed and the band of

frequencies where VSWR is 1:1.5 (or required VSWR)is called its band width.

For Example if an antenna is designed for a frequency of 780 MHZ and the VSWR value

is from 750 MHz to 810 MHz then Band width

Bandwidth = F2- F1

F2= Upper band frequency

F1=lower band frequency

For above example bandwidth= 810-750 MHz=60 MHz.

4.6 BEAM WIDTH

Beam width will be measured only for directional and Bi-directional antenna.

Erect the antenna as shown in the drawing below. Switch on the sweep

generator to centre frequency of the antenna to be tested and sufficient R.F.output. One

antenna is connected to the output of sweep generator. And one more antenna of the same

type and same frequency is erected exactly opposite and at the same height as the

transmitting antenna located at a distance of 3-5 Meters. The second antenna is a

receiving antenna and should be connected to a signal strength meter or a Spectrum

Analyzer through a feeder cable . A disc with 360 º mark is kept at the bottom of the

mast of the receiving antenna which is the antenna under test and a pointer to indicate the

degrees is fixed. The direction of Rx antenna is rotated slightly on both sides to obtain the

maximum signal level as indicated on the spectrum analyzer. Then adjust the disc so that

pointer is against zero on the disc. Rotate mast Rx slowly till the signal level on

spectrum analyzer falls by 3 dB. Note the degrees on the disc opposite to the pointer.

Rotate the mast in the opposite direction till the signal strength falls by 3 dB on the other

side and note the degrees opposite to the pointer. The total degrees from one end to the

other end are the total beam width of the antenna. Test set up as shown in the below

diagram.

Fig4.6:Beamwidth and front to back ratio Measurement setup

4.7 FRONT TO BACK RATIO

Proceed as explained above and erect the Tx and Rx antennas. Adjust the Rx

antenna for maximum signal strength and set the disc to zero. Note the signal level on

spectrum analyzer of the Rx antenna. Rotate Rx antenna to 180 º . Note the signal level

on the spectrum analyzer and the difference in the levels is the Front to Back ratio in dB.

Test set up as shown in the above drawing.

4.8 GAIN MEASUREMENT

Erect the Tx and Rx antennas as shown in the below. Rotate the Rx antenna (the

antenna under test) for maximum signal level and note down the readings.

Substitute the Rx antenna with a standard dipole. The length of the dipole shall

be adjusted to the mid frequency with standard scale. Note the signal level and the

difference between the two levels is the gain of the antenna in dBd. Add 2.2 dB to obtain

dBi. Test set up as shown in the figure.

Fig4.8:Gain Measurement Setup

CHAPTER :5

BLOCK DIAGRAM DISCRIPTION

Fig5.1:Block diagram comprises of transmitter section and receiver section as

shown in figure

5.1 TRANSMITTER

A transmitter is an electronic device which, usually with the aid of an antenna, propagates

an electromagnetic signal such as radio, television, or other telecommunications.

Generally in communication and information processing, a transmitter is any object

(source) which sends information to an observer (receiver). When used in this more

general sense, vocal cords may also be considered an example of a transmitter.

In radio electronics and broadcasting, a transmitter usually has a power supply, an

oscillator, a modulator, and amplifiers for audio frequency (AF) and radio frequency

(RF). The modulator is the device which piggybacks (or modulates) the signal

information onto the carrier frequency, which is then broadcast. Sometimes a device (for

example, a cell phone) contains both a transmitter and a radio receiver, with the

combined unit referred to as a transceiver. In amateur radio, a transmitter can be a

separate piece of electronic gear or a subset of a transceiver, and often referred to using

an abbreviated form; "XMTR". In most parts of the world, use of transmitters is strictly

controlled by laws since the potential for dangerous interference (for example to

emergency communications) is considerable. In consumer electronics, a common device

is a Personal FM transmitter, a very low power transmitter generally designed to take a

simple audio source like an iPod, CD player, etc. and transmit it a few feet to a standard

FM radio receiver. Most personal FM transmitters in the United States fall under Part 15

of the Federal Communications Commission (FCC) regulations to avoid any user

licensing requirements.

In industrial process control, a "transmitter" is any device which converts measurements

from a sensor into a signal, conditions it, to be received, usually sent via wires, by some

display or control device located a distance away. Typically in process control

applications the "transmitter" will output an analog 4-20 mA current loop or digital

protocol to represent a measured variable within a range. For example, a pressure

transmitter might use 4 mA as a representation for 50 psig of pressure and 20 mA as 1000

psig of pressure and any value in between proportionately ranged between 50 and 1000

psig. (A 0-4 mA signal indicates a system error.) Older technology transmitters used

pneumatic pressure typically ranged between 3 to 15 psig (20 to 100 kPa) to represent a

process variable.

5.1.1 Microphone

A microphone (colloquially called a mic or mike )is an acoustic-to-electric transducer or

sensor that converts soundinto an electrical signal. In 1876, Emile Berliner invented the

first microphone used as a telephone voice transmitter. Microphones are used in many

applications such as telephones, tape recorders, karaoke systems, hearing aids, motion

picture production, live and recorded audio engineering, FRS radios, megaphones, in

radio and television broadcasting and in computers for recording voice, speech

recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock

sensors. Most microphones today use electromagnetic induction (dynamic microphone),

capacitance change (condenser microphone, pictured right), piezoelectric generation, or

light modulation to produce an electrical voltage signal from mechanical vibration.

Condenser Microphones

Condenser means capacitor, an electronic component which stores energy in the form of

an electrostatic field. The term condenser is actually obsolete but has stuck as the name

for this type of microphone, which uses a capacitor to convert acoustical energy into

electrical energy.

Condenser microphones require power from a battery or external source. The

resulting audio signal is stronger signal than that from a dynamic. Condensers also tend

to be more sensitive and responsive than dynamics, making them well-suited to capturing

subtle nuances in a sound. They are not ideal for high-volume work, as their sensitivity

makes them prone to distort.

Fig 5.1.1 Condenser Microphone

How Condenser Microphones Work

A capacitor has two plates with a voltage between them. In the condenser mic, one of

these plates is made of very light material and acts as the diaphragm. The diaphragm

vibrates when struck by sound waves, changing the distance between the two plates and

therefore changing the capacitance. Specifically, when the plates are closer together,

capacitance increases and a charge current occurs. When the plates are further apart,

capacitance decreases and a discharge current occurs.

A voltage is required across the capacitor for this to work. This voltage is supplied

either by a battery in the mic or by external phantom power.

5.1.2 Audio Amplifier

An audio amplifier is an electronic amplifier that amplifies low-power

audio signals (signals composed primarily of frequencies between 20 hertzto 20,000

hertz, the human range of hearing) to a level suitable for driving loudspeakers and is the

final stage in a typical audio playback chain.

The preceding stages in such a chain are low power audio amplifiers which perform tasks

like pre-amplification, equalization, tone control,mixing/effects, or audio sources

like record players,CD players, and cassette players. Most audio amplifiers require these

low-level inputs to adhere toline levels.

While the input signal to an audio amplifier may measure only a few hundred microwatts,

its output may be tens, hundreds, or thousands of watts.

IC LA 4510

Applications

• Especially suited for use in 3V micro cassette recorder,

mini cassette recorder, headphone stereo applications.

Features

• Operating supply voltage range : 2 to 5V.

• Low current dissipation (7mA typ/VCC=3V).

• Output power :

240mW typ at VCC=3V, RL=4W, THD=10%

40mW typ at VCC=3V, RL=32W, THD=10%

• Built-in muting circuit to be operated at the time of power switch ON capable of

varying starting time and making pop noise low.

5.1.3 OSCILLATORS

Introduction

Oscillators can generally be categorised as either amplifiers with positive feedback

satisfying the wellknown Barkhausen Criteria (Ref. 1), or as negative resistance circuits

(Ref. 2). Both concepts are illustrated At RF and Microwave frequencies the negative

resistance design technique is generally favoured.

Fig 5.1.3 Oscillator

The procedure is to design an active negative resistance circuit which, under large-signal

steady-state conditions, exactly cancels out the load and any other positive resistance in

the closed loop circuit. This leaves the equivalent circuit represented by a single L and C

in either parallel (as illustrated) or series configuration. At a frequency the reactances will

be equal and opposite, and this resonant frequency is given by the standard formula;

It can be shown that in the presence of excess negative resistance in the small-signal

state, any small perturbation caused, for example, by noise will rapidly build up into a

large signal steady-state resonance given by equation Negative resistors are easily

designed by taking a three terminal active device and applying the correct amount of

feedback to a common port, such that the magnitude of the input reflection coefficient

becomes greater than one. This implies that the real part of the input impedance is

negative . The input of the 2-port negative resistance circuit can now simply be

terminated in the opposite sign reactance to complete the oscillator circuit. Alternatively

high-Q series or parallel resonator circuits can be used to generate higher quality and

therefore lower phase noise oscillators. Over the years several RF oscillator

configurations have become standard. The Colpitts, Hartly and Clapp circuits are

examples of negative resistance oscillators shown here using bipolars as the active

devices. The Pierce circuit is an op-amp with positive feedback, and is widely utilised in

the crystal oscillator industry

Fig 5.1.3 RF oscillators

This paper will now concentrate on a worked example of a Clapp oscillator, using a

varactor tuned ceramic coaxial resonator for voltage control of the output frequency. The

frequency under consideration will be around 1.4 GHz, which is purposely set in-between

the two important GSM mobile phone frequencies. It has been used at Plextek in Satellite

Digital Audio Broadcasting circuits, and in telemetry links for Formula One racing cars.

At these frequencies it is vital to include all stray and parasitic elements early on in the

simulation. For example, any coupling capacitances or mutual inductances affect the

equivalent L and C values in equation, and therefore the final oscillation frequency.

Likewise, any extra parasitic resistance means that more negative resistance needs to be

generated.

5.1.4 Amplitude Modulation

Amplitude modulation or AM as it is often called, is a form of modulation used for radio

transmissions for broadcasting and two way radio communication applications. Although

one of the earliest used forms of modulation it is still in widespread use today.

With the introduction of continuous sine wave signals, transmissions improved

significantly, and AM soon became the standard for voice transmissions. Nowadays,

amplitude modulation, AM is used for audio broadcasting on the long medium and short

wave bands, and for two way radio communication at VHF for aircraft. However as there

now are more efficient and convenient methods of modulating a signal, its use is

declining, although it will still be very many years before it is no longer used.

In order that a radio signal can carry audio or other information for broadcasting or for

two way radio communication, it must be modulated or changed in some way. Although

there are a number of ways in which a radio signal may be modulated, one of the easiest,

and one of the first methods to be used was to change its amplitude in line with variations

of the sound.

The basic concept surrounding what is amplitude modulation, AM, is quite

straightforward. The amplitude of the signal is changed in line with the instantaneous

intensity of the sound. In this way the radio frequency signal has a representation of the

sound wave superimposed in it. In view of the way the basic signal "carries" the sound or

modulation, the radio frequency signal is often termed the "carrier".

Fig5.1.4 Amplitude Modulation, AM

 

When a carrier is modulated in any way, further signals are created that carry the actual

modulation information. It is found that when a carrier is amplitude modulated, further

signals are generated above and below the main carrier. To see how this happens, take the

example of a carrier on a frequency of 1 MHz which is modulated by a steady tone of 1

kHz.

The process of modulating a carrier is exactly the same as mixing two signals together,

and as a result both sum and difference frequencies are produced. Therefore when a tone

of 1 kHz is mixed with a carrier of 1 MHz, a "sum" frequency is produced at 1 MHz + 1

kHz, and a difference frequency is produced at 1 MHz - 1 kHz, i.e. 1 kHz above and

below the carrier.

If the steady state tones are replaced with audio like that encountered with speech of

music, these comprise many different frequencies and an audio spectrum with

frequencies over a band of frequencies is seen. When modulated onto the carrier, these

spectra are seen above and below the carrier.

It can be seen that if the top frequency that is modulated onto the carrier is 6 kHz, then

the top spectra will extend to 6 kHz above and below the signal. In other words the

bandwidth occupied by the AM signal is twice the maximum frequency of the signal that

is used to modulated the carrier, i.e. it is twice the bandwidth of the audio signal to be

carried.

Advantages of Amplitude Modulation, AM

There are several advantages of amplitude modulation, and some of these reasons have

meant that it is still in widespread use today:

It is simple to implement

it can be demodulated using a circuit consisting of very few components

AM receivers are very cheap as no specialised components are needed.

5.1.5 Mixers

The function of the mixer is to convert the receiver RF signal to a fixed frequency IF, by

mixing it with a locally-generated oscillator signal (local oscillator, or LO). This means

that selective filtering, most of the system gain, and demodulation can all be carried out

at a convenient fixed frequency. Generally, when two signals are combined in a non-

linear element, other frequencies are generated , the principal of these being the sum and

the difference between the two input frequencies. For example, if frequencies of 100MHz

and 145MHz are mixed, we get 245MHz and 45MHz at the output. Either of these could

be selected as our IF but, for receiver applications, it would be usual to choose 45MHz.

The higher frequency would selected for a transmitter (up-converter).

Usually the IF is at a lower frequency than the input RF, but this is not always the case.

Sometimes, where a very broad tuning range is required (such as in a multi-band HF

communications receiver), it is more convenient to use a first IF of 45MHz, say, and then

to convert down again in a second mixer. Using a high first IF and a second conversion

has other benefits.

5.1.6 The Power Amplifier.

The last active device in the transmitter chain is generally known as the Power Amplifier

(PA). This device (sometimes there are two, as in a balanced amplifier) provides the

specified RF output power to the antenna. Transmitter output power is generally defined

as the power fed to a resistive dummy load, connected at the antenna port. Inevitably,

there will be losses between the PA and the antenna port (PIN switch and/or

filter/duplexer). A good design will make every effort to minimize these losses, but the

actual PA power may need to be 2 - 3dB higher than the specified output power. Thus,

for 10 watts output, the PA will need to deliver 16 - 20 watts.

Matching.

In order to deliver maximum power, the device should be ‘matched’ at input and output.

Figures will be given on the manufacturer’s data sheet for input and output impedances

under different operating conditions. As these impedances are usually ‘complex’, it is

important to remember that the matching network must be the conjugate of the given

figures. For example, a transistor having a Zout = 5 + j3 needs a matching impedance of

5 - j3. The output will generally be matched to 50Ω, but sometimes it is convenient to

match the input directly to the driver impedance (non-50Ω). In calculating values for the

matching network, it is helpful to use a Smith Chart and there are several useful

programs that will do this on your PC. Another factor to be considered is the ‘Q’ of the

matching network. For a single frequency, the Q can be quite high, but where a

transmitter is required to operate over a wide band of frequencies, the Q will need to be

low. It is no use matching the transmitter at band center if there is a serious mismatch at

the band extremities. Low Q is achieved by using two or more sections] in the matching

network. The effect of this can easily be seen on the Smith Chart, when Q curves are

displayed. A link to a free program, QuickSmith, is given in section 3.17 (Appendices).

At microwave frequencies, lumped elements (capacitors, inductors) become unsuitable as

tuning] components and are used primarily as chokes and bypasses. Matching, tuning,

and filtering at microwave frequencies are therefore accomplished with distributed

(transmission-line) networks. It is common to use a transmission line between the device

and load to provide the desired matching value. A stub that is a quarter-wavelength at the

frequency of interest and open at one end provides a short circuit. Similarly, a quarter-

wavelength shorted at one end provides an open circuit. Stubs that are less than a quarter-

wavelength behave as capacitors.

Advantages:

1. Guaranteed performance.

2. Extremely compact size.

3. 50Ω input and output impedances (requires no matching).

Disadvantages:

1. May not be available for less popular frequency bands.

2. Single source manufacturer.

3. Can be more expensive than discrete equivalent.

PA Efficiency and Class of operation.

The bias conditions for the PA stages and the mode of operation are generically defined

by “class”. Definition of the various classes is as follows:

Class A.

When the active device is biased for linear operation, such that any small change at its

input causes a corresponding, but much larger change at its output, this is defined as

Class A operation. When this is applied to a PA stage, a constant high current will flow

through the device. Maximum power will be when the load equals the (resistive) output

impedance of the device and the peak-to-peak output voltage is equal to the supply

voltage (less any volt-drop across the active device itself). Maximum stage efficiency is

25% and, for good linear performance, may drop to 15 - 20%.

Class B.

For Class B operation, the active device is biased at the cut-off point (i.e. zero current)

and conducts only during the positive half of the drive cycle. In the absence of a ‘tank’

circuit, this would act like an inverting half-wave rectifier and only negative-going half

cycles would appear at the output. The tank actually comprises a matching network with

a ‘Q’ value greater than unity and preferably at least 3. To recover the missing half cycle,

the tank allows the supply voltage to over-swing by an amount equal to the negative

excursion, thus effectively doubling the supply voltage and hence the available RF output

voltage. Since the actual dc supply does not change and average current remains the

same, it follows that the PA efficiency is doubled to 50%. Again, this is an ideal figure

and actual efficiency may be more like 45%.

Class AB.

In Class AB, the active device is biased such that it is just turned on, but the quiescent

current is very much lower than for a Class A amplifier. Class AB is not linear, and so

could not be used where a linear amplifier is required. Its benefit is that it is more

efficient than a Class A stage, but requires less drive power than Class B or Class C.

Class C.

Class C operation is very similar to Class B, except that the active device is biased

beyond cut-off. With discrete silicon transistors, this condition is conveniently achieved

by simply omitting any dc bias components and returning the base-drive input to ground

through an RF choke, or resistor. The drive voltage will cause base current to flow during

the positive half-cycle and the rectifying action of the base-emitter junction will result in

a negative dc voltage on the base. The angle of conduction will depend upon the

amplitude of the drive voltage and the value of resistance in the return path. Thus, a large

value of resistor would cause a large negative bias and the transistor would conduct only

on the tips of the drive waveform, resulting in little or no output power. A low value of

resistor will result in a larger angle of conduction and, with zero ohms, the bias will

effectively be the fixed Vb-e of the transistor itself (about 0.7V). For adequate drive to

achieve the desired power output, the conduction angle should not be less than 60°, where

a PA efficiency of up to 70% is possible. See Class C output stages are quite common for

FM (or FSK) transmitters in the VHF and low UHF bands, but as the operating frequency

is increased, it becomes difficult to achieve sufficient gain in

the PA stages without using some forward bias. For very high power transmitters using

vacuum tubes, a fixed negative supply voltage is required to achieve Class C operation.

A Class C power amplifier for the 440MHz band. Self-bias is produced by conduction at

the base-emitter junction and is proportional to the drive current and the value of base

resistor. A 2-stage PA for 1.8GHz, using FET’s and transmission line matching elements.

Note that this is not operating in Class C - these devices require a negative gate voltage

for normal conduction.

Class D.

A Class D PA uses two or more transistors as switches to generate a square-wave at the

transmitter frequency. A series-tuned output filter passes only the fundamental-frequency

component to the load. Current is drawn only through the transistor that is on, resulting in

a theoretical 100% efficiency for an ideal PA. If the switching is sufficiently fast,

efficiency is not degraded by reactance in the load, but practical PA’s suffer from losses

due to saturation, switching speed, and output capacitance. Finite switching speed causes

the transistors to be in their active regions while conducting current. Output capacitances

must be charged and discharged once per RF cycle, resulting in power loss that is

proportional to, and increases directly with frequency. Class D PA’s with power outputs

of 100 W to 1 kW are readily implemented at HF, but are seldom used above lower VHF

because of the losses associated with output capacitance.

Class E.

Class E employs a single transistor operated as a switch. The load voltage waveform is

the result of the sum of the dc and RF currents charging the load shunt capacitance. For

optimum performance, the PA voltage drops to zero and has zero slope just as the

transistor turns on. The result is an ideal efficiency of 100%, elimination of the losses

associated with charging the load capacitance in class D, reduction of switching losses,

and good tolerance of component variation. Variations in load impedance and shunt

susceptance cause the PA to deviate from optimum operation, but the capability

for efficient operation in the presence of significant drain capacitance makes class E

useful in some applications. High-efficiency HF PA’s with power levels to 1 kW can be

implemented using low-cost MOSFETs intended for switching rather than RF use. Class

E has been used for high-efficiency amplification in the PA for a 900MHz CDMA

handset, using a single GaAs-HBT RFIC that includes a single-ended

Class-AB PA.

A typical PA module produces 28 dBm (631 mW) at full output with a typical PA

efficiency of 35 - 50%. A useful (free) design program may be found at

Page 70

Class F.

Class F boosts both efficiency and output by using harmonic resonators in the output

network to shape the waveforms. The voltage waveform includes one or more odd

harmonics and approximates a square wave, while the current includes even harmonics

and approximates a half sine wave. Alternately (inverse class F), the voltage can

approximate a half sine wave and the current a square wave. As the number of harmonics

increases, the theoretical efficiency increases from 50% toward 100% (e.g., 70.7, 81.65,

86.56, 90.45 for two, three, four, and five harmonics, respectively). The required

harmonics arise naturally from non-linearity and saturation in the transistor. While class

F requires a more complex output filter than other PA’s, the impedances at the “virtual

drain” must be correct at only a few specific frequencies. A variety of modes of operation

in-between classes C, E, and F are possible.

5.2 REGULATED POWER SUPPLY

The micro controller IC requires a 5v of regulated voltage for its function.

To provide regulated voltage we go for R.P.S. It consists of a step down transformer and

a rectifier circuit and a filter circuit and a regulator circuit.

Fig5.2 Regulated Power supply

Working:

Power supply circuit provides a required constant voltage to a load. The circuit

consists of step down transformer which takes the input from AC mains and down

converts it to 12V (which is required). The bridge rectifier circuit converts AC signal to

DC signal of 12V. IC 78XXis a three terminal positive voltage regulator and XX

indicates the output voltage of the regulator. The capacitor acts as filter that allows only

DC signal to pass. IC 7812 regulates the voltage of 12V which is required by the stepper

motor to overcome initial torque. IC 7805 regulates the voltage to 5V.when the switch is

ON, the LED glows and 5V is given to the load. A resistor placed in series with the LED

in order to protect the LED, which requires only 2V.The remaining 3V is dropped across

the resistor. The final 5V is given to 31st and 40Th pin of 8051 microcontroller, stepper

motor and LCD display.

5.2.1 Transformer

A transformer makes use of Faraday's law and the ferromagnetic properties of an

iron core to efficiently raise or lower AC voltages. It of course cannot increase power so

that if the voltage is raised, the current is proportionally lowered and vice versa.

Fig5.2.1 Transformer

Transformers with primary and secondary windings of identical inductance, give

approximately equal voltage and current levels in both circuits. Equality of voltage and

current between the primary and secondary sides of a transformer, however, is not the

norm for all transformers. If the inductances of the two windings are not equal, something

interesting happens:

This is a very useful device, indeed. With it, we can easily multiply

or divide voltage and current in AC circuits. Indeed, the transformer has made long-

distance transmission of electric power a practical reality, as AC voltage can be "stepped

up" and current "stepped down" for reduced wire resistance power losses along power

lines connecting generating stations with loads. At either end (both the generator and at

the loads), voltage levels are reduced by transformers for safer operation and less

expensive equipment. A transformer that increases voltage from primary to secondary

(more secondary winding turns than primary winding turns) is called a step-up

transformer. Conversely, a transformer designed to do just the opposite is called a step-

down transformer.

5.2.2 RECTIFIERS

A d.c. power supply is used for operating all digital circuit applications using BJTS ,or

FETS .The d.c voltage needed are in the range of +18V to -18V.In digital circuits,

particularly for the TTL gates the d.c voltage required is +5V. Use batteries is an solution

for supplying power to the transistor circuits, and in fact in large number of applications

they are .Unfortunately batteries run down very fast when currents are drawn and the

only convenient source of power is the 230V, 50Hz a.c supply mains. The a.c. signal is

stepped down, rectified, filtered and regulated to give the required d.c voltage.

Semiconductor diodes are invariably used as rectifiers for lower voltages in the transistor

circuits.

HALF WAVE RECTIFIER

The circuit consists of a diode with the load resistance R in series

Fig5.2.3 Half Wave Rectifier

The 230V,50Hz a.c is stepped down to Vac by a transformer and applied to the

diode. The diode conducts only when the voltage at its anode is positive with respect to

the cathode. In most of the analysis to follow we shall neglect the small cut-in voltage of

the diode in comparison to the Vac.the diode current Id ,is positive and unidirectional.

The output voltage Vo across the load resistance will be IdR. The output voltage will

have the same wave shape as the signal for the positive half cycle and zero otherwise.

FULLWAVE RECTIFIER

The circuit arrangement in the half wave rectifier is such that the current is driven into

the load only during half the cycle. By the full wave rectifier arrangement it is possible to

get this difficulty and drives the load during the positive and negative half cycles of the

input. The circuit consists of a centre tapped transformer. During the positive half cycle,

the diode D1 conducts and the current flows into the load R. The voltage at the anode of

diode D2 is negative throughout this positive cycle and hence it is cut-off. During the

negative half cycle the voltage at the anode of D2 is positive and it conducts. Thus, the

load current and hence the voltage across R is unidirectional.

Between the two rectifier circuits, the half wave and the full wave –the voltage output,

ripple factor and the efficiency of the full wave rectifier is superior. An additional factor

in favour of the full wave rectifier circuit is that equal current flows through the two

halves of the centre tapped secondary of the transformer and consequently d.c.

saturation of the core is avoided. Half wave rectifier has the advantage of a simpler

circuitry and lower cost.

The frequency components other than the zero frequency must be reduced by some

method in order to provide a useful d.c. voltage at the output .The simplest technique will

be to filter out the unwanted frequencies by a low pass filter.

BRIDGE RECTIFIER

As the name suggests the four diodes are connected in a bridge and circuit is a full wave

rectifier. One of the main feature of the bridge rectifier is that it does not require a centre

tap transformer. On the positive half of the cycle, the current flows from A through

D1,R,D2 and back to B. During the negative half cycle the current flows from B through

D3,R,D4 and back to A. The current through the load R is in the same direction the two

half cycles. When D1 and D2 conduct the diodes D3 and D4 are reverse biased and vice-

versa. The peak inverse voltage across the diode is Vm only whereas it was 2Vm in the

full wave rectifier circuit. The current flows all the time in the secondary of the

transformer of the bridge rectifier , as against the full wave rectifier where the current

flows half the time in each winding of the centre-tapped transformer. The current rating

of the transformer in the bridge rectifier is thus about 2/3 of the rating of the same

transformer in the full wave circuit.

5.2.3 FILTER CIRCUIT

Low-Pass Filter

Figure  3.2 shows one possible low-pass filter. The circuit is essentially a

frequency-sensitive voltage divider. At high frequencies the output behaves as if it

is shorted while at low frequencies the output appears as an open circuit.

Fig5.2.3 (a)RC low-pass filter

Mathematically we have

High-Pass Filter

Fig 5.2.3 (b):  RC high-pass filter.

At low and high frequencies

At the corner frequency we have

5.3 RECEIVER

5.3.1 TUNED CIRCUIT

To understand tuned circuits, we first have to understand the phenomenon of self-

induction. And to understand this, we need to know about induction.The first discovery

about the interaction between electric current and magnetism was the realization that an

electric current created a magnetic field around the conductor. It was then discovered that

this effect could be enhanced greatly by winding the conductor into a coil. The effect

proved to be two-way: If a conductor, maybe in the form of a coil was placed in a

changing magnetic field, a current could be made to flow in it; this is called induction.

So imagine a coil, and imagine that we apply a voltage to it. As current starts to flow, a

magnetic field is created. But this means that our coil is in a changing magnetic field, and

this induces a current in the coil. The induced current runs contrary to the applied current,

effectively diminishing it. We have discovered self-induction. What happens is that the

self-induction delays the build-up of current in the coil, but eventually the current will

reach its maximum and stabilize at a value only determined by the ohmic resistance in the

coil and the voltage applied. We now have a steady current and a steady magnetic field.

During the buildup of the field, energy was supplied to the coil, where did that energy

go? It went into the magnetic field, and as long as the magnetic field exists, it will be

stored there.

Now imagine that we remove the current source. Without a steady

current to uphold it, the magnetic field starts to disappear, but this means our coil is again

in a variable field which induces a current into it. This time the current is in the direction

of the applied current, delaying the decay of the current and the magnetic field till the

stored energy is spent. This can give a funny effect: Since the coil must get rid of the

stored energy, the voltage over it rises indefinitely until a current can run somewhere!

This means you can get a surprising amount of sparks and arching when coils are

involved. If the coil is large enough, you can actually get an electric shock from a low-

voltage source like an ohmmeter.

Self-inductance is measured in henry (H or Hy). A henry is almost as enourmous value as

a Farad, and coils are often measured in milli, micro and even nanohenry.

An LC circuit is a resonant circuit or tuned circuit that consists of an

inductor, represented by the letter L, and a capacitor, represented by the letter C. When

connected together, an electric currentcan alternate between them at the circuit's resonant

frequency.

LC circuits are used either for generating signals at a particular

frequency, or picking out a signal at a particular frequency from a more complex signal.

They are key components in many applications such as oscillators, filters, tuners and

frequency mixers. An LC circuit is an idealized model since it assumes there is no

dissipation of energy due to resistance. For a model incorporating resistance see RLC

circuit.

Operation:

An LC circuit can store electrical energy vibrating at its resonant frequency. A capacitor

stores energy in the electric field between its plates, depending on the voltage across it,

and an inductor stores energy in itsmagnetic field, depending on the current through it.

If a charged capacitor is connected across an inductor, charge will start to flow through

the inductor, building up a magnetic field around it, and reducing the voltage on the

capacitor. Eventually all the charge on the capacitor will be gone and the voltage across it

will reach zero. However, the current will continue, because inductors resist changes in

current, and energy will begin to be extracted from the magnetic field to keep it flowing.

The current will begin to charge the capacitor with a voltage of opposite polarity to its

original charge. When the magnetic field is completely dissipated the current will stop

and the charge will again be stored in the capacitor, with the opposite polarity as before.

Then the cycle will begin again, with the current flowing in the opposite direction

through the inductor.

The charge flows back and forth between the plates of the

capacitor, through the inductor. The energy oscillates back and forth between the

capacitor and the inductor until (if not replenished by power from an external circuit)

internal resistance makes the oscillations die out. Its action, known mathematically as a

harmonic oscillator, is similar to a pendulum swinging back and forth, or water sloshing

back and forth in a tank. For this reason the circuit is also called a tank circuit. The

oscillations are very fast, typically hundreds to billions of times per second.

LC Tuned Circuit

An LC circuit is a resonant circuit or tuned circuit that consists of an inductor,

represented by the letter L, and a capacitor, represented by the letter C. When connected

together, an electric currentcan alternate between them at the circuit's resonant frequency.

LC circuits are used either for generating signals at a particular frequency, or picking out

a signal at a particular frequency from a more complex signal. They are key components

in many applications such as oscillators, filters, tuners and frequency mixers. An LC

Fig5.3.1 LC oscillator

circuit is an idealized model since it assumes there is no dissipation of energy due

to resistance. For a model incorporating resistance 

An LC circuit can store electrical energy vibrating at its resonant frequency. A capacitor

stores energy in the electric field between its plates, depending on the voltage across it,

and an inductor stores energy in itsmagnetic field, depending on the current through it.

If a charged capacitor is connected across an inductor, charge will start to flow through

the inductor, building up a magnetic field around it, and reducing the voltage on the

capacitor. Eventually all the charge on the capacitor will be gone and the voltage across it

will reach zero. However, the current will continue, because inductors resist changes in

current, and energy will begin to be extracted from the magnetic field to keep it flowing.

The current will begin to charge the capacitor with a voltage of opposite polarity to its

original charge. When the magnetic field is completely dissipated the current will stop

and the charge will again be stored in the capacitor, with the opposite polarity as before.

Then the cycle will begin again, with the current flowing in the opposite direction

through the inductor.

The charge flows back and forth between the plates of the capacitor,

through the inductor. The energy oscillates back and forth between the capacitor and the

inductor until (if not replenished by power from an external circuit)

internal resistance makes the oscillations die out. Its action, known mathematically as

a harmonic oscillator, is similar to a pendulum swinging back and forth, or water sloshing

back and forth in a tank. For this reason the circuit is also called a tank circuit. The

oscillations are very fast, typically hundreds to billions of times per second.

5.3.2 DETECTOR

A detector is a device that recovers information of interest contained in

a modulated wave. The term dates from the early days of radio when all transmissions

were in Morse code, and it was only necessary to detect the presence (or absence) of a

radio wave using a device such as a coherer without necessarily making it audible. A

more up-to-date term is "demodulator", but "detector" has a history of many decades of

use, even if it is a misnomer.

Envelope detector

One major technique is known as envelope detection. The simplest form of envelope

detector is the diode detector that consists of a diode connected between the input and

output of the circuit, with a resistor and capacitor in parallel from the output of the circuit

to the ground. If the resistor and capacitor are correctly chosen, the output of this circuit

will approximate a voltage-shifted version of the original signal.

An early form of envelope detector was the cat's whisker, which was used in the crystal

set radio receiver.

Product detector

A product detector is a type of demodulator used for AM and SSB signals. Rather than

converting the envelope of the signal into the decoded waveform like an envelope

detector, the product detector takes the product of the modulated signal and a local

oscillator, hence the name. At least partially, it multiplies the signal by the output of the

local oscillator. This can be accomplished by heterodyning. The received signal is mixed,

in some type of nonlinear device, with a signal from the local oscillator, to produce

an intermediate frequency, referred to as the beat frequency, from which the modulating

signal is detected and recovered.

5.3.3 Amplitude demodulation

Amplitude modulation, AM, is one of the most straightforward ways of modulating a

radio signal or carrier. The process of demodulation, where the audio signal is removed

from the radio carrier in the receiver is also quite simple as well. The easiest method of

achieving amplitude demodulation is to use a simple diode detector. This consists of just

a handful of components:- a diode, resistor and a capacitor.

 

Fig5.3.3 AM Diode Detector

In this circuit, the diode rectifies the signal, allowing only half of the alternating

waveform through. The capacitor is used to store the charge and provide a smoothed

output from the detector, and also to remove any unwanted radio frequency components.

The resistor is used to enable the capacitor to discharge. If it were not there and no other

load was present, then the charge on the capacitor would not leak away, and the circuit

would reach a peak and remain there.

5.3.4 AUDIO AMPLIFIER

An audio amplifier is an electronic amplifier that amplifies low-power

audio signals (signals composed primarily of frequencies between 20 hertzto 20,000

hertz, the human range of hearing) to a level suitable for driving loudspeakers and is the

final stage in a typical audio playback chain.

The preceding stages in such a chain are low power audio amplifiers which perform tasks

like pre-amplification, equalization, tone control,mixing/effects, or audio sources

like record players,CD players, and cassette players. Most audio amplifiers require these

low-level inputs to adhere toline levels.

While the input signal to an audio amplifier may measure only a few hundred microwatts,

its output may be tens, hundreds, or thousands of watts.

5.3.5 SPEAKER

A speaker driver is an individual transducer that converts electrical energy to sound

waves, typically as part of a loudspeaker, television, or other electronics device.

Sometimes the transducer is itself referred to as a speaker, particularly when a single one

is mounted in an enclosure or as surface-mounted device (as in a wall-mounted

speaker, car audio speaker, and so on). There are many different types of speaker drivers.

The most common ones are the woofer, mid-range and tweeter, as well

as subwooferswhich are becoming very common. Less common types of speaker drivers

are supertweeters and rotary woofers, a new technology that is

still proprietary of Eminent Technology.

Description and operation

Cut-away view of a dynamic loudspeaker

Fig5.3.5 Speaker

Speaker drivers include a diaphragm that moves back and forth to create pressure

waves in the air column in front, and depending on the application, at some angle to the

sides. The diaphragm is typically in the shape of a cone or, less commonly, a ribbon or a

dome, and is usually made of coated or uncoated paper or polypropylene plastic.[1] More

exotic materials are used on some drivers, such as woven fiberglass, carbon

fiber, aluminum, titanium, and a very few use PEI, polyimide, PET film plastic film as

the cone, dome or radiator.

All speaker drivers have a means of electrically inducing back-and-forth motion.

Typically there is a tightly wound coil of insulated wire (known as a voice coil) attached

to the neck of the driver's cone. In a ribbon speaker the voice coil may be printed or

bonded onto a sheet of very thin paper, aluminium, fiberglass or plastic. This cone, dome

or other radiator is mounted to a rigid chassis which supports a permanent magnet in

close proximity to the voice coil. For the sake of efficiency the relatively lightweight

voice coil and cone are the moving parts of the driver, whereas the much heavier magnet

remains stationary. Other typical components are a spider or damper, used as the rear

suspension element, simple terminals or binding posts to connect the audio signal, and

possibly a compliant gasket to seal the joint between the chassis and enclosure.

Drivers are almost universally mounted into a rigid enclosure of wood, plastic, or

occasionally metal. This loudspeaker enclosure or speaker box isolates the acoustic

energy from the front of the cone from that of the the back of the cone. A horn may be

employed to increase efficiency and directionality. A grille, fabric mesh, or other

acoustically neutral screen is generally provided to cosmetically conceal the drivers and

hardware, and to protect the driver from physical damage.

In operation, a signal is delivered to the voice coil by means of electrical wires. The

current creates a magnetic field that causes the diaphragm to be alternately attracted to,

and repelled by, the fixed magnet as the electrical signal varies. The resulting back-and-

forth motion drives the air in front of the diaphragm, resulting in pressure differentials

that travel away as sound waves.

Speaker drivers may be designed to operate within a broad or narrow frequency range.

Small diaphragms are not well suited to moving the large volume of air that is required

for satisfying low frequency response. Conversely, large drivers may have heavy voice

coils and cones that limit their ability to move at very high frequencies. Drivers pressed

beyond their design limits may have high distortion. In a multi-way loudspeaker system,

specialized drivers are provided to produce specific frequency ranges, and the incoming

signal is split by a crossover.[1] Drivers can be sub-categorized into several types: full-

range, tweeters, super tweeters, mid-range drivers, woofers, and subwoofers.

CHAPTER: 6LOG PERIODIC DIPOLE ARRAY (LPDA)

6.1 INTRODUCTION

The log-periodic dipole array (LPDA) consists of a system of driven elements, but not all

elements in the system are active on a single frequency of operation. Depending upon its

design parameters, the LPDA can be operated over a range of frequencies having a ratio

of 2:1 or higher, and over this range its electrical characteristics — gain, feed-point

impedance, front-to-back ratio, etc. - will remain more or less constant. This is not true of

any Multielement Directive Array Antenna, for either the gain factor or the front-to-back

ratio, or both, deteriorate rapidly as the frequency of operation departs from the design

frequency of the array. And because the antenna designs discussed earlier are based upon

resonant elements, off-resonance operation introduces reactance which causes the SWR

in the feeder system to increase.

The log-periodic array consists of several dipole elements which each are of different

lengths and different relative spacings. A distributive type of feeder system is used to

excite the individual elements. The element lengths and relative spacings, beginning from

the feed point for the array, are seen to increase smoothly in dimension, being greater for

each element than for the previous element in the array. It is this feature upon which the

design of the LPDA is based, and which permits changes in frequency to be made

without greatly affecting the electrical operation. With changes in operating frequency,

there is a smooth transition along the array of the elements which comprise the active

region.

A good LPDA may be designed for any band, hf to uhf, and can be built to meet the

amateur’s requirements at nominal cost: high forward gain, good front-to-back ratio, low

VSWR, and a boom length equivalent to a full sized three-element Yagi. The LPDA

exhibits a relatively low SWR (usually not greater than 2 to 1) over a wide band of

frequencies. A well-designed LPDA can yield a 1.3-to-l SWR over a 1.8-to-1 frequency

range with a typical directivity of 9.5 dB. (Directivity is the ratio of maximum radiation

intensity in the forward direction to the average radiation intensity from the array.

Assuming no resistive losses in the antenna system, 9.5 dB directivity equates to 9.5 dB

gain over an isotropic radiator or approximately 7.4 dB gain over a half-wave dipole.

6.2 DESIGN AND CONSTRUCTION OF THE LPDA

The design principles of the LPDA are well established. The LPDA is an array of dipoles

connected to a common transmission line fed from the apex of the array.

The transmission line from the feed must alternate which side of the line

connects to which side of the dipole in order to get the correct phasing to create an

antenna that radiates in the direction of the array apex. The transmission line consisted of

two strip conductors, one on

either side of the board. By putting one half of each dipole on either side of the board and

connecting it to the transmission line strip, and alternating which half dipole went on

which

side of the board, the alternating feed connection was obtained.

Fibre-glass board (r = 4.5) 1/16 inch thick was used to construct the LPDA. The

required frequency range of the LPDA was 900 MHz to 3GHz which meant that the

dipole elements, based on a free space wavelength could easily be accommodated on the

200 mm by 300 mm printed circuit board used.

Fig 6.2 . LPDA AntennaThe LPDA is frequency independent in that the electrical properties such as the mean

resistance level, RO , characteristic impedance of the feed line ZO , and driving-point

admittanceYO , vary periodically with the logarithm of the frequency. As the frequency f1

is shifted to another frequency f2 within the passband of the antenna, the relationship is f2

= f1 /

= a design parameter, a constant; <l.0. Also

f1= lowest frequency fn= highest frequency

The design parameter is a geometric constant near 1.0 which is used to determine the

element lengths, l , and element spacings, d , as shown in Fig. That is,

Where ln= shortest element length, and

Where = spacing between elements 2 and 3.

Where , l = element length

h = element half length

d = element spacing

= design constant

= relative spacing constant

S = feeder spacing

Zo = characteristic impedance of antenna feeder

Each element is driven with a phase shift of 180° by switching or alternating element

connections, as shown in Fig. 1. The dipoles near the input, being nearly out of phase and

close together nearly cancel each others’ radiation. As the element spacing, d, expands

there comes a point along the array where the phase delay in the transmission line

combined with the 180° switch gives a total of 360°. This puts the radiated fields from

the two dipoles in phase in a direction toward the apex. Hence a lobe coming off the apex

results.

This phase relationship exists in a set of dipoles known as the “active region.” If we

assume that an LPDA is designed for a given frequency range, then that design must

include an active region of dipoles for the highest and lowest design frequency. It has a

bandwidth which we shall call ar (bandwidth of the active region).

Assume for the moment that we have a 12-element LPDA. Currents flowing in the

elements

are both real and imaginary, the real current flowing in the resistive component of the

impedance of a particular dipole, and the imaginary flowing in the reactive component.

Assume that the operating frequency is such that element number 6 is near to being

halfwave

resonant. The imaginary parts of the currents in shorter elements 7 to 12 are capacitive,

while those in longer elements 1 to 6 are inductive. The capacitive current components in

shorter elements 9 and 10 exceed the conductive components hence, these elements

receive little power from the feeder and act as parasitic directors. The inductive current

components in longer elements 4 and 5 are dominant and they act like parasitic reflectors.

Elements 6, 7 and 8 receive most of their power from the feeder and act like driven

elements. The amplitudes of the currents in the remaining elements aresmall and they

may be ignored as primary contributors to the radiation field. Hence, we have a

generalized Yagi array with seven elements comprising the active region. It should be

noted that this active region is for a specific set of design parameters ( = 0.93, =

0.175). The number of elements making up the active region will vary with and .

Adding additional elements on either side of the active region cannot significantly modify

the circuit or field properties of the array.

This active region determines the basic design parameters for the array, and sets the

bandwidth for the structure, s. That is, for a design frequency coverage of bandwidth ,

there exists an associated bandwidth of the active region such that

fig:6.3

ar varies with and as shown in Fig. 2. Element lengths which fall outside ar play

an insignificant role in the operation of the array. The gain of an LPDA is determined by

the design parameter and the relative element spacing constant . There exists an

optimum value for, opt , for each in the range 0.8 < < 1.0, for which the gain is

maximum; however, the increase in gain achieved by using opt and near 1.0 (i.e., =

0.98) is only 3 dB above isotropic (3 dBi) when compared with the minimum ( min

= .05) and = 0.9, shown in Fig.

An increase in means more elements and optimum means a long boom. A high-gain

(8.5

dBi) LPDA can be designed in the hf region with = 0.9 and s = .05. The relationship of

, , and is as follows:

where 1/2 the apex angle= design constant= relative spacing constant

The method of feeding the antenna is rather simple. As shown in Fig. , a balanced feeder

is required for each element, and all adjacent elements are fed with a 180° phase shift by

alternating element connections. In this section the term antenna feeder is defined as that

line which connects each adjacent element. The feed line is that line between antenna and

transmitter. The characteristic impedance of the antenna feeder, Z O, must be determined

so that the feed-line impedance and type of balun can be determined. The antenna-feeder

impedance Z O depends on the mean radiation resistance level R O (required input

impedance of the active region elements - see Fig. 4) and average characteristic

impedance of a dipole, Z a. ( Z a is a function of element radius a and the resonant element

half length, where h 4. The relationship is as follows:

where Z O = characteristic impedance of feeder

R O = mean radiation resistance level or required input impedance of the active

region.

Z O = average characteristic impedance of a dipole

h = element half lengtha = radius of element

From Fig. we can see that R O decreases with increasing and increasing . Also the

VSWR with respect to R O has a minimum value of about 1.1 to 1 at optimum, and a

value of 1.8 to 1 at = .05. These SWR values are acceptable when using standard

RG8/U 52-ohm and RG-11/U 72-ohm coax for the feed line. However, a one-to-one

VSWR match can be obtained at the transmitter end using a coax-to-coax Transmatch. A

Transmatch will enable the transmitter low-pass filter to see a 52-ohm load on each

frequency within the array passband. The Transmatch also eliminates possible harmonic

radiation caused by the frequency-independent nature of the array.

Once the value of Z O has been determined for each band within the array

passband, the

balun and feed line may be chosen. That is, if Z O = 100 ohms, a good choice for the

balun would be 1 to 1 balanced to unbalanced, and 72-ohm coax feed line. If Z O = 220

ohms, choose a 4 to 1 balun, and 52-ohm coax feed line, and so on. The balun may be

omitted if the array is to be fed with an open-wire feed line.

The terminating impedance, Z t , may be omitted. However, if it is used, it should

have a length no longer than max/8. The terminating impedance tends to increase the

front-tobac ratio for the lowest frequency used. For hf-band operation a 6-inch shorting

jumper wire may be used for Z t . When Z t is simply a short-circuit jumper the longest

element behaves as a passive reflector. It also might be noted that one could increase the

frontto- back ratio on the lowest frequency by moving the passive reflector (No. 1

element) a distance of 0.15 to 0.25 behind element No. 2, as would be done in the case

of an ordinary Yagi parasitic reflector. This of course would necessitate lengthening the

boom. The front-to-back ratio increases somewhat as the frequency increases. This is

because more of the shorter inside elements form the active region, and the longer

elements become additional reflectors.

6.3 DESIGN PROCEDURE

A systematic step-by-step design procedure of the LPDA follows. This procedure may be

used for designing any LPDA for any desired bandwidth.

1) Decide on an operating bandwidth between f1, lowest frequency and fn, highest

Frequency.

2) Choose and to give a desired gain

The value of opt may be determined

3) Determine the apex half-angle

4) Determine the bandwidth of the active group ar

5) Determine the structure (array) bandwidth s

6) Determine the boom length, L, number of elements, N, and longest element length, l1.

where max = longest free-space wavelength = 984/1. Examine L, N and l1, and

determine whether or not the array size is acceptable for your needs. If the array is too

large, increase by 5° and repeat steps 2 through 6.

7) Determine the terminating stub Z t . (Note: For hf arrays short out the longest

element with a 6-inch jumper. For vhf and uhf arrays use: Z t = max 8

8) Once the final values of and are found, the characteristic impedance of the feeder Z

O must be determined so the type of balun and feed line can be found. Determine R O from

Fig. , Z a from Fig. and . Note: Values for h /a, Z a, and Z O must be determined for each

amateur band within the array passband. Choose the element half-length h nearest h =

/4, at the center frequency of each amateur band. Once Z O is found for each band,

choose whatever combination of balun and feed line will give the lowest SWR on each

band.

9) Solve for the remaining element lengths

l0) Determine the element spacing from

and the remaining element-to-element spacings

FIGURE 6.3 RADIATION PATTERNFig. — Measured radiation pattern for the lowest frequency band (14 MHz) of a 12-

element 13-30 MHz log-periodic dipole array. For its design parameters, = 0.9 and

= .05. The measured front-to-back ratio is 14.4 dB at 14 MHz, and increases to 21 dB at

28 MHz. This completes the design. The measured radiation pattern for a 12-element

LPDA is shown in Fig.

There are several high-gain array possibilities using this type of antenna as a basis.

Tilting the elements toward the apex will increase the gain 3 to 5 dB. Adding parasitic

directors and a reflector will increase both gun and front-to-back ratio for a specific

frequency within the passband. The LPDA-Yagi combination is very simple. Use the

LPDA design procedures within the set of driven elements, and place parasitic elements

at normal Yagi spacings from the LPDA end elements. Use standard Yagi design

procedures for the parasitic elements. An example of a single-band high-gain LPDA-Yagi

would be a twoor three- element LPDA for 21.0 to 21.45 MHz with the addition of 2 or 3

parasitic directors and one parasitic reflector. The combinations are endless.

CHAPTER: 7

LPDA Antenna Testing

7.1 Network analyzer

A network analyzer is an instrument used to analyze the properties of electrical

networks, especially those properties associated with the reflection and transmission of

electrical signals known as scattering parameters (S-parameters).

Fig 7.1 Network analyser

Network analyzers are used mostly at high frequencies; operating frequencies can range

from 9 kHz to 110 GHz.[1] Special types of network analyzers can also cover lower

frequency ranges down to 1 Hz. These network analyzers can be used for example for the

stability analysis of open loops or for the measurement of audio and ultrasonic

components.[2]

The two main types of network analyzers are

Scalar Network Analyzer (SNA) — measures amplitude properties only

Vector Network Analyzer (VNA) — measures both amplitude and phase

properties

A VNA may also be called a gain-phase meter or an Automatic Network Analyzer. An

SNA is functionally identical to a spectrum analyzer in combination with a tracking

generator. As of 2007, VNAs are the most common type of network analyzers, and so

references to an unqualified “network analyzer” most often mean a VNA

A microwave network analyzer (HP 8720A) showing a Smith chart

A new category of network analyzer is the Microwave Transition Analyzer (MTA) or

Large Signal Network Analyzer (LSNA), which measure both amplitude and phase of

the fundamental and harmonics. The MTA was commercialized before the LSNA, but

was lacking some of the user-friendly calibration features now available with the LSNA

7.2 DIRECTIONAL COUPLER

A directional coupler separates signals based on the direction of signal propagation.

These devices are used to unequally split the signal flowing in the mainline and to fully

pass the signal flowing in the opposite direction. In an ideal situation some portion of the

signal flowing into port A will appear at Port C. Likewise any signal flowing into port C

will be coupled fully to port A. However ports B and C are isolated in that any signal

flowing into port B will not appear at port C but will feed through to port A. The generic

RF directional coupler symbol, shown in Figure 1(a), is usually realized by two

transformers connected as shown in Figure 1(b). Directional couplers of

Fig7.2 . Directional coupler circuit configurations

7.3 VSWR

Voltage Standing Wave Ratio (VSWR) is the ratio of the maximum voltage to the

minimum voltage in the standing wave on a transmission line. Standing waves are the

result of reflected RF energy. As the VSWR approaches 1.00:1, the reflections on the line

approach zero and maximum power may be transmitted.

VSWR READINGS FOR ANTENNA : I

Frequency MHz VSWR

400 2.2

450 1.4

500 1.3

550 1.6

600 1.3

650 2.0

700 1.3

750 1.3

800 1.4

850 1.8

900 2.4

950 2.5

1000 2.5

VSWR READINGS FOR ANTENNA : II

Frequency MHz VSWR

400 1.5

450 1.6

500 1.5

550 1.5

600 1.6

650 1.7

700 1.5

750 1.9

800 1.5

850 2.1

900 2.2

950 1.7

1000 2.3

7.5 OPERATING WAVELENGTH

λmax =c/f(min) = 0.75 m or 75 Cm

σ = 0.08 τ = 0.82

7.6 APEX ANGLE(α)

Cot (α) = 4σ / (1- τ) = 1.77

α = 29.55˚7.7 LENGTH OF ANTENNA

L1 (length of first element) = λ / 2 = 75 / 2 = 37.5 Cm ( on both sides)

(On one side)l1 = L1/2 = 18.75Cm

(length of second element on one side) = l2 = τ* l1

7.8 DISTANCE BETWEEN TWO ELEMENTS

d12 (Distance between 1st and 2nd element) = ½ (L1 - L2)cotα = 5.9 Cm

d23 (Distance between 2nd and 3rd element) = d12*τ = 4.8 Cm

7.9 CONCLUSION

In this report, we have provide an overview of some important issues on wireless

communication using LPDA antenna. Miniaturization is expected to progress until

saturation, which usually occurs after the third or fourth iteration. Additional iterations

provide little benefits when compared to the design effort and to the printed circuit board

fabrication accuracy. As with most antennas, miniaturization comes at an expense. Here,

this expense is reflected upon a) a slightly higher cross-polarization field component,

mostly at nonboresight directions, b) a higher VSWR which is enhanced by the loading

of the feedline and the few elements in the antenna’s active region, and c) a gain reduced

by 0.3 dBi due to the slightly larger beamwidth and the increased VSWR.

The miniaturization concept of such antennas, however, was shown and can be

extended to more wideband and/or directive designs using more radiating elements. Such

designs will have similar levels of cross-polarization (i.e., around 20 dB or less) and

always very low at boresight (around 30 dB or less). Even with these shortcomings, the

miniaturized LPDA performs well and covers the entire frequency range with constant

gain, as expected from a conventional LPDA. This concept enables investigations on

more compact LPDAs. Meander and “zig-zag” dipoles that fill more efficiently the

antenna volume are candidate elements that give potential to this letter. The structure of

the LPDA is planar and relatively simple to fabricate using standard PCB fabrication

techniques. It can also be directly integrated with planar microwave circuits. The design

concept can easily be scaled for applications with different bandwidth and/or directivity

requirements by adjusting the angle and by adding more elements, which shall also

improve the VSWR.

We have keeping in mind the various hurdles in antenna design have

achieved our aim to create a working module of a wireless communication system using

LPDA antenna with the required specifications of high gain and increased bandwidth.

REFERNCES

1.Antenna Theory (3rd edition), by C. Balanis, Wiley, 2005, ISBN 0-471-66782-X;

2.Antenna Theory and Design (2nd edition), by W. Stutzman and G. Thiele, Wiley,

1997, ISBN 0-471-02590-9;

3.Antennas (3rd edition), by J. Kraus and R. Marhefka, McGraw-Hill, 2001, ISBN 0-072-

32103-2;

4.Antennenbuch, by Karl Rothammel, publ. Franck'sche Verlagshandlung Stuttgart,

1991, ISBN 3-440-05853-0; other editions (in German)

5.Antennas for portable Devices, Zhi Ning Chen (edited), John Wiley & Sons in March

2007

6.Broadband Planar Antennas: Design and Applications, Zhi Ning Chen and M. Y. W.

Chia, John Wiley & Sons in February 2006

7.The ARRL Antenna Book (15th edition), ARRL, 1988, ISBN 0-87259-207-5