relector antennas

12008 2008

First edition

Ahmed M. AlaaAhmed M. Alaa

2

F I r s t e d I t I o n

Fundamental

Types of AntennasTypes of Antennas

By Ahmed M.Alaa

3

Contents Contents

Introduction …. 8 Chapter 1 : Basic antenna terminology ………..9

1.1 Radiation pattern1.2 Directivity 1.3 Gain 1.4 Efficiency

1.5 Types of antennas

Chapter 2 : Dipole antenna ………..34

2.1 Introduction 2.2 Balanced and Unbalanced Systems 2.3 Image theory

2.4 Monopoles 2.5 Disadvantages

4

Contents Contents

Chapter 3 : Loop antennas………..61

3.1 Introduction 3.1 Introduction 3.2 Design Parameters3.2 Design Parameters3.3 Equivalent Circuits 3.3 Equivalent Circuits 3.4 Loop antenna 3.4 Loop antenna

ConfigurationsConfigurations 3.5 Applications in mobile3.5 Applications in mobile

Communication systemCommunication system

Chapter 4 : Yagi Uda antennas………..77

4.1 Introduction 4.1 Introduction 4.2 Components4.2 Components

4.3 Design procedure4.3 Design procedure4.4 Advantages4.4 Advantages

4.5 The folded dipole4.5 The folded dipole

5

Contents Contents

Chapter 5 : Reflector antennas………..92

5.1 Why Reflectors ? 5.1 Why Reflectors ? 5.2 Types of reflectors5.2 Types of reflectorsAccording to geometryAccording to geometry5.3 Types of Parabolic5.3 Types of Parabolic

SurfacesSurfaces 5.4 Methods of feeding5.4 Methods of feeding

Parabolic reflectorsParabolic reflectors5.5 Using Image theory5.5 Using Image theory

To calculate field To calculate field 5.6 Using GTD to calculate5.6 Using GTD to calculate

The field The field

6

Contents Contents

Chapter 6 : Microstrip antennas………..105

6.1 Components 6.1 Components 6.2 Types of microstrip 6.2 Types of microstrip

AntennasAntennas6.3 Feeding techniques6.3 Feeding techniques6.4 Advantages 6.4 Advantages 6.5 Disadvantages 6.5 Disadvantages

6.6 Techniques to overcome6.6 Techniques to overcomeDisadvantages Disadvantages

6.7 Microstrip arrays 6.7 Microstrip arrays 6.8 Feeding of arrays 6.8 Feeding of arrays

6.9 Microstrip vs. reflectors.6.9 Microstrip vs. reflectors.

7

Contents Contents

Chapter 7 : Fractal antennas………..130

7.1 Definition 7.1 Definition 7.2 Characteristics7.2 Characteristics

7.3 Types of fractals7.3 Types of fractals7.4 Advantages7.4 Advantages

8

Introduction Introduction

This book presents a collection of presentations I gave And tutorials I made previously for basic

concepts of Antenna design , it shows you a conceptual overview for Each type of antennas

and software programs that you Can use to design them , their advantages , Disadvantages and applications they are used in without Involving any complicated equations. The book can be

Considered a quick guide for amateur antenna designers Or readers interested in

understanding how antennas Work with no prerequisites …

9

Chapter 1Chapter 1

Thomas Edison usedAntennas in 1885 !

Basic antenna terminology

10

Basic AntennaBasic Antennaterminologyterminology

OutlineOutline

1. Radiation Pattern 1. Radiation Pattern 2. Directivity2. Directivity

3. Gain3. Gain4. Efficiency 4. Efficiency

5. Types of antennas5. Types of antennas

11

1.1 Radiation Pattern 1.1 Radiation Pattern

The distribution of power or it’s Derivatives ( power density , powerIntensity ) in the space around theAntenna , relative to the maximum Magnitude , i.e. : Radiation patternIs concerned with the proportion

Of magnitudes and not their values..The pattern varies according to

Different and .

An example to a radiation pattern in Cartesian coordinates

12

Radiation Pattern Radiation Pattern

An example to a radiation pattern in Polar coordinates

Azimuth plane

Elevation plane

13

Radiation Pattern Radiation Pattern

An example to a 3DRepresentation of a

Radiation pattern.

14

Radiation Pattern : Radiation Pattern : Half power beam widthHalf power beam width

The beam width is the angle included between two angles in which u (, ) Is equal to half Umax , where U is the power intensity . The half power beam

Width = 1 -2 . Where 1 and 2 are the angles where U is half its Max value , the same for the elevation angle .

The Half power beam widths are : a – Azimuth plane beam width b – Elevation plane beam width

15

Radiation Pattern : Radiation Pattern : Half power beam widthHalf power beam width

When the pattern’s mathematical formula is independent on phi , the patternIs symmetric about the z – axis , then the Azimuth plane beam width is equal

To the elevation plane beam width .

Calculating Azimuth plane beam width

Putting = / 2 , we can calculate Phi 1 and Phi 2

Putting =/ 2 , we can calculate Theta 1 and Theta 2

Calculating elevation plane beam width

16

Radiation Pattern : Radiation Pattern : Azimuth plane half power beam widthAzimuth plane half power beam width

17

Radiation Pattern : Radiation Pattern : Elevation plane half power beam widthElevation plane half power beam width

18

Radiation Pattern : Radiation Pattern : First Null beam width First Null beam width

The beam included by angles where the power is ZERO , usually the firstNulls bound the major lobe of the radiation pattern , the first null beam width

Is calculated by estimating the angles where the power intensity isZero .

19

Radiation Pattern : Directive AntennasRadiation Pattern : Directive Antennas

Some Applications we need the receiving or transmitting process to be Directed in a certain direction , the radiation pattern then have a major lobe

With most of the power concentrated in a certain beam .

20


Side lobes : lobesThat have lower

Power than major Lobes ( also called

Minor lobes ) .

Back lobe : TheLobe directed To the earth in

3D representation

Major lobes : theLobes with highest

Power concentration( usually present inDirective antennas)

The decart plot of a directive antenna

21


The 3D plot of a directive antenna

22

Radiation Pattern : Radiation Pattern : Omindirectional AntennasOmindirectional Antennas

Antennas are said to be omindirectional when the power is distributed Equally around the antenna without being concentrated within a certain

Beam .

23


The decart plot of an omindirectional antennaThe distribution of power

Around the antennaIs nearly equal .

24


The 3D plot of an omindirectional antenna

25

1.2 . Directivity1.2 . Directivity

Directivity : The measure of how much power , power density or powerIntensity is concentrated in a certain beam

D = Umax / Uo Where Uo is the average power intensity and Umax is maximum intensity

When Umax = Uo , the antenna is omindirectional & D = 1 = 0 dB .

26

DirectivityDirectivity

The directivity is usually inversely proportional with the half power beam width D ( 1 / HPBW )

U ( ,)

U ( ,)

Ideal case D = Infinity , and HPBW

= 0 . ( a Pulse where ALL

Power is concentratingAt one point .)

Omindirectional

27

1.3 . Gain1.3 . Gain

Gain : The directivity after considering the antennas efficiency .

G = D * Usually measured in dB .

28

1.4 . Efficiency1.4 . Efficiency

The Efficiency of an Antenna is divided into three parts :a – Radiation Efficiency

b – Mismatch c – Polarization losses .

29

Efficiency : Radiation Efficiency Efficiency : Radiation Efficiency

Radiation Efficiency : The efficiency of the antenna itself , regardless ofThe antenna system , and the polarization mismatch , it is related to the

Material of the antenna .

Radiation Efficiency =

( Radiated Power )/ ( Radiated Power +

Lost Power ) .

Sometimes called = ecd

30

Efficiency : Reflection Mismatch Efficiency : Reflection Mismatch

When an antenna is connected to a generator , the transmission line used causesa reflection in the impedance of the antenna if the characteristic impedance ofThe transmission line ( Zo ) differs from the input impedance of the antenna

( Z in ) . The input impedance is transformed by Zin = ( Zo * Zo ) / Zold .

= | ( Zin – Zo ) / ( Zin + Zo ) |

er = 1 - | | 2

Reflection Coefficient

ReflectionEfficiency

31

Efficiency : Reflection Mismatch Efficiency : Reflection Mismatch

~

Zo

Zin

An equivalent circuit for an Antenna attached to a Generator , the input

Impedance of the load ( antenna ) is not equal toZin but the transmission

Line transforms it accordingTo its characteristic

Impedance Zo .

32

Efficiency : Polarization losses Efficiency : Polarization losses

If the Polarization of the incident wave is not matching with the polarization ofThe antenna , losses results in and measured by polarization loss factor

PLF .

Antenna Polarization Received Signal

Cross -Polar Component

Co – Polar Component

Lost Component

PLF = Cos

33

1.5 . Types of Antennas1.5 . Types of Antennas

1 – Wire Antennas

3 – Microstrip Antennas

5 – Reflector Antennas

2 – Aperture Antennas

4 – Array Antennas

6 – Lens Antennas .

34

Chapter 2Chapter 2

C.A.Balanis is one ofThe most important

antenna scientists , andContributed with a

famous book “Antenna theory”.

Dipole antenna

35

Dipole AntennaDipole AntennaOutlineOutline

1. Introduction2. Balanced and

Unbalanced Systems3. Image theory

4. Monopoles5. Disadvantages

Practical Example

36

2.1. Introduction2.1. Introduction

The dipole antenna is the simplest antenna , despite of not being used Practically in applications , it is used to test antenna labs ( so it is consideredThe reference antenna ) , a dipole antenna consists of 2 wires ( lambda /4 for

Its length ) , the two wires are separated by a gap and their terminals are Connected to the transmitter or the receiver

/ 4

/ 4

This type of dipoles is calledHalf wave length dipole as the

Total length is lambda / 2 .

+-

37

Introduction : Geometry Introduction : Geometry

38

Introduction : dipole configurationIntroduction : dipole configuration

39

IntroductionIntroduction :: CharacteristicsCharacteristics

The directivity is nearly equal to 1.6 1.6 dimensionless and about 2 -> 2.2 dB2.2 dB ,The input impedance is usually 73 + 42.5 j73 + 42.5 j ohms and the radiation resistance

Is nearly 7373 ohm .

40

Introduction : Radiation PatternIntroduction : Radiation Pattern II

The dipole is an Electric field Antenna , that means that the magnetic field isZero at the near field . The radiation pattern is like a donut cake with the maximum

Perpendicular to the dipole , and a null along it .The polarization is along the dipole .

The 3D plot of the radiation Pattern of a dipole antenna .The 3D plot of the radiation Pattern of a dipole antenna .

41

Introduction : Radiation PatternIntroduction : Radiation Pattern II

The radiation pattern for the Electric field for a folded dipole

antenna

The radiation pattern for the Electric field for a folded dipole

antenna

42

IntroductionIntroduction : Radiation Pattern II: Radiation Pattern II

The radiation pattern of the dipole , all the field is electric as shown .The radiation pattern of the dipole , all the field is electric as shown .

43

The radiation pattern of the dipole , the magnetic field equals zero .The radiation pattern of the dipole , the magnetic field equals zero .

No radiationNo radiationPattern for thePattern for theMagnetic fieldMagnetic field

“ “ H “ !! H “ !! This means thatThis means that

A dipole is anA dipole is anElectric field Electric field Antenna … Antenna …

IntroductionIntroduction : Radiation Pattern III: Radiation Pattern III

44

IntroductionIntroduction : Radiation Pattern IV: Radiation Pattern IV

When the length of the dipole exceeds lambda the radiation pattern takes A new shape due to the appearance of the grating lobesgrating lobes where the major

Lobes divides into multiple lobes .

When the length of the dipole exceeds lambda the radiation pattern takes A new shape due to the appearance of the grating lobesgrating lobes where the major

Lobes divides into multiple lobes .

45

A system with two input terminals , a positive and negative terminals , the Dipole antenna is a balanced system because it has two terminals and this

Is why it is not widely used in applications .

2.2 . Balanced and Unbalanced Systems2.2 . Balanced and Unbalanced Systems

Balanced System

Balanced System

+-

2 input terminals

46

Balanced and Unbalanced SystemsBalanced and Unbalanced Systems

Unbalanced System

A system with one input terminal , having a single pole and a ground plane , we desire an unbalanced system because when mounting an antenna in a

Device only one input will is used for each component and all components haveA common ground .

Unbalanced System 1 input terminal

47

Balanced and Unbalanced Systems : Balanced and Unbalanced Systems : BalunsBaluns

48

2.3 . Image theory2.3 . Image theory

When a single pole is near an infinite plane conductor , virtual sources ( images )Will be introduced to account for their reflections , the plane conductor can be

Considered a ground and thus we can construct an antenna that have the sameBehavior of a dipole but having a single pole , this type of antennas is called

Monopoles Monopoles , and have the advantage of being an unbalanced system .

ConductorsConductors FieldsFields

Electric conductorPECPEC

Magnetic ConductorsPMCPMC

Electric field

Magnetic field

49

Image theoryImage theory

= infinity = infinity

When electric and magnetic fields are near electric and magnetic fields their Images are in the following directions :

PECPECPMCPMC

50

2.4 . Monopoles 2.4 . Monopoles

When combining actual and image sources , an equivalent system of a dipoleIs resulted and actually resembles the behavior of a dipole but with using a

Single pole and having the advantage of being an unbalanced system , this isWhy monopoles are more practically used than dipoles .

A direct ray from the Actual source to theObservation point

Represents the firstPole of a dipole .

A reflected ray from theGround plane to the Same observation

Point , has the same Effect of a virtual source Representing the second

Pole .

51

Monopoles Monopoles

52

Monopoles Monopoles

MonopoleMonopole DipoleDipole

Zin = 36.5 + 21.25j

Zin = 73+ 42.5j

53

Monopoles Monopoles

The radiation pattern of a monopole is half the radiation pattern of a dipole If we imagined that the radiation pattern of a dipole is a donut cake , the Monopole’s radiation pattern is a half eaten donut !! . In a dipole theta is

Defined from 0 to 180 , in monopoles theta is defined from 0 to 90 .

54

Monopoles : Coaxial cables ( Coax )Monopoles : Coaxial cables ( Coax )

Co – axial cables consists of a central and a ground plane , it is used to connectThe monopole to the load ( ex: a TV ) .

Ground plane

Central cable

Dielectric material

55


We benefit from the ground plane of cable by welding it to the ground of monopoleAnd welding it to the ground of monopoles and welding the central cable to the

Wire ( the monopole ) .

Ground plane

Central cable

56


We can even make a monopole from just a co – axial cable !

Central cable And the pole ofThe monopole Antenna at the

Same time..

Ground plane Of the monopole And the ground

Plane of the coaxAt the same time..

~

Equivalent toEquivalent to

57

Monopoles : Baluns Monopoles : Baluns

When we use a dipole instead of a monopole , we should use a balunbalun , whichIs a device that converts a balanced system to an unbalanced system , the

Word balun is the abbreviation of “ BalBalanced to UnUnbalanced converter “.

Balanced System Balun

58

2.5 . Disadvantages2.5 . Disadvantages

An Electric field antenna , this means that the magnetic field “ H “ isZero at near field , this makes dipoles incompatible with portable

Combination .

Dipoles are balanced systems , this makes it difficult to mount themOn any device without the use of baluns .

59

Practical Example Practical Example

Try connecting a terminal of a cable like the one shown in the figure to a port in your TV , the other terminal acts as a monopole ( but with a bad

Performance ) , and you can enjoy watching your TV …!!

60

Practical Example Practical Example

When designing your dipole or monopole , you can reduce the length of your

Design by covering it with a dielectric material with permittivity , the length

Is reduced then by 1 /

Dielectric coverMaterial…

Dielectric coverMaterial…Antenna with

Reduced length .Antenna with

Reduced length .

61

Chapter 3Chapter 3

C.A.Balanis is one ofThe most important

antenna scientists , andContributed with a

famous book “Antenna theory”.

Loop antenna

62

Loop AntennasLoop AntennasOutlineOutline

1. Introduction 1. Introduction 2. Design Parameters2. Design Parameters3. Equivalent Circuits 3. Equivalent Circuits

4. Loop antenna 4. Loop antenna ConfigurationsConfigurations

5. Applications in mobile5. Applications in mobileCommunication systemCommunication system

Practical ExamplePractical Example

63

3.1. Introduction3.1. Introduction

As the dipole is the reference ( conventional ) electric field antenna , loopsAre the reference magnetic field antenna . Loop antennas can take different shapes

Like square , circle , triangle , ellipse or any other closed shape.

In dipoles currentMoves till

discontinuity occurs

And then radiates( Electric field ).

When current Circulates in the Loop it is obviousThat a magnetic Field is produced.

i

i

64

IntroductionIntroduction : Geometry : Geometry

65

Introduction : Radiation Pattern Introduction : Radiation Pattern

A small loop is equivalent to an infinitesimal magnetic dipole , whose axis Perpendicular to the plane of the loop.

The elevation and azimuth Plane radiation pattern of a

Loop antenna .

66

Introduction : Radiation PatternIntroduction : Radiation Pattern

The 3D radiationPattern of loop

Antenna , showing The geometry ofThe loop in blue.

67

IntroductionIntroduction : Radiation Pattern : Radiation Pattern

The radiation patternOf a loop for magneticField , the dominant

Radiation is magneticAnd this is why

Loops are magneticField antennas .

68


Types of loops are :

Electrically Small Electrically large

C < / 10C : circumference C ~

69

3.2. Design Parameters3.2. Design Parameters

The radiation resistanceradiation resistance of loop antennas is very small and sometimesLess than the loss resistance , this makes them receivers rather than

Transmitters where signal to noise ratio is more important than efficiency .signal to noise ratio is more important than efficiency .

Methods of increasing radiation resistance :

1 – Increasing its perimeter (electrically)2 – Increasing number of turns

3 – Inserting a ferrite core with highPermeability ( ferrite loops ).

70

Design ParametersDesign Parameters

Design parameters :

1 – 1 – Perimeter of the loop ( circumference).

3 – 3 – Spacing between turns .

2 – 2 – Increasing number of turns.

4 – 4 – Thickness .

5 – 5 – Presence of a ferrite core .

71


The effect of design parameters on added resistanceadded resistance :

Ron : Normalized Added resistance.

N : Number of turns

N = 8N = 7

N = 6

1.0 1.5 2.0 2.5 3.0

Ron

Spacing

We seek a design with theMinimum spacing and

Maximum turns to satisfy Maximum radiation resistance.

72


Resistance

Inductance

Capacitance

Reactance

Resonance occurs When the capacitance

And inductance Vanishes and

resistance is maximumThis is the

Area we select theDesign within

ImpedanceImpedance

Thickness to circumference ratioThickness to circumference ratio

73

3.3. Equivalent Circuits 3.3. Equivalent Circuits

As we saw the transmitting mode can bemodeled by a parallel resonance circuit

Transmitting mode

Rr

RlZg

Vg

++

XaXa

CC

--

74

Equivalent Circuits Equivalent Circuits

Receiving mode

Vg

Zg

Zload

++

--

75

3.4. Loop Antenna Configurations3.4. Loop Antenna Configurations

Top – driven triangularTop – driven triangular Base – driven triangularBase – driven triangular

RectangularRectangular CircularCircular

~ ~

~~

76

3.5. Loops in mobile communication3.5. Loops in mobile communication

1 – Loops are alternative to monopoles , the most widelyUsed element for hand held portable mobile

Communication.

2 – Loops are used in portable pagers , but very few inTransceivers due to high resistance and inductance.

3 – Loops are very immune to noise , having low noiseTo signal ratio makes them suitable for interfering

And fading environment.

77

Chapter 4Chapter 4

The Yagi Antenna is a The Yagi Antenna is a directionaldirectional

antenna invented byantenna invented by Dr. Hidetsugu Dr. Hidetsugu Yagi of Tohoku Yagi of Tohoku

Imperial Imperial University and hisUniversity and his

assistant, Dr. Shintaro Uta.assistant, Dr. Shintaro Uta.

Yagi antenna

78

Yagi – UdaYagi – Uda AntennasAntennas

OutlineOutline

1 – Introduction1 – Introduction2 – Components2 – Components

3 – Design procedure3 – Design procedure4 – Advantages4 – Advantages

5 – The folded dipole5 – The folded dipole

79

4.1 . Introduction 4.1 . Introduction

One of the most popular antennas used in home TV is the yagi uda array , it is A very practical radiator in the HF ( 3 – 30 MHz ) , VHF ( 30 – 300 MHz) and

UHF ( 300 – 3000 MHz ) ranges .

The Yagi – uda antenna is primarily an array of linear dipoles with one elementServing as the feed while the others act as parasitic elements .

80


This arrangement extends for arrays of loops , an antenna that is very popular Among ham radio operators is the quad antenna .

~

Driven Driven

Reflectors Reflectors

81

4.2 . Components 4.2 . Components

The yagi uda antenna consists of a number of linear dipole elements :

-One of which is energized directly by a feed transmission line while the others actas parasitic radiators whose currents are induced by mutual coupling .

-Parasitic radiators are divided into reflectors and directors. -The feed element is usually a type of dipoles called a folded dipole used

For operation in the end fire mode .

~Driven Driven

Reflector Reflector Directors Directors

82

Components : geometry Components : geometry

83

Components : 3D display Components : 3D display

84

4.3 . Design procedure4.3 . Design procedure

To achieve the end fire mode the design is characterized by :To achieve the end fire mode the design is characterized by :

Parasitic elements in the direction of the beam are smaller than feed element ( directors )

The driven element is slightly less than / 2 ( ~ 0.45 – 0.49 )

The directors should be about ( ~ 0.4 – 0.45 ) ; less than the feed element

85

Design procedureDesign procedure

The separation between the directors is between 0.3 to 0.4 lambda .

A yagi uda array of 6 lambda total length was found to have an overall gainIndependent on the directors’ separation

The length of the reflector is somewhat greater than the feed element

The directors are not necessarily of the same length or diameter !

86


Most antennas has from 6 to 12 directors .

The separation between the feed element and the reflector is less than that ofThe feed and the nearest director ( nearly 0.25 lambda )

87


The 3D radiation pattern

88


The 2D radiation pattern

89


The SWR plot of the yagi uda

90

4.4 . Advantages 4.4 . Advantages

Light weightedLight weighted

Simple to buildSimple to build

Low cost .Low cost .

91

4.5 . The folded dipole 4.5 . The folded dipole

~The folded dipole is frequently used as the feeding element

As it has good directional characteristics , it is Recommended that the width << lambda .

92

Chapter 5Chapter 5

The first cassegrain The first cassegrain Reflector was designedReflector was designedBy Laurent cassegrain By Laurent cassegrain

In 1672 .In 1672 .

Reflector antenna

93

ReflectorReflector AntennasAntennas

OutlineOutline

1- Why Reflectors ?1- Why Reflectors ?

2 –2 – Types of reflectorsTypes of reflectorsAccording to geometryAccording to geometry

3 – Types of Parabolic3 – Types of ParabolicSurfacesSurfaces

4 – Methods of feeding4 – Methods of feedingParabolic reflectorsParabolic reflectors

5 – Using Image theory5 – Using Image theoryTo calculate field To calculate field

6 – Using GTD to calculate6 – Using GTD to calculateThe field The field

94

5.1. Why Reflectors ? 5.1. Why Reflectors ?

While using aperture antennas we always need to increase the apertureArea to increase its directivity ,but as this is not practical , instead of usingLarge apertures we place a reflecting surface face to face with the aperture

( or any other antenna ) , the reflecting surface collimates radiation toThe small aperture and thus we satisfied high directivity with a small

Aperture , and overcame space limitations.

A side view ofA side view ofAn aperture ofAn aperture ofA large area A large area

A side view ofA side view ofAn aperture ofAn aperture ofA small area A small area

And a reflectingAnd a reflectingSurface used.Surface used.

95

5.2. Types according to geometry 5.2. Types according to geometry

Plane reflectorsPlane reflectors Corner reflectors Corner reflectors

Curved reflectorsCurved reflectors

96

Types according to geometry : Types according to geometry : 90 degree corner90 degree corner

To better collimate the energy in the forward direction , the geometrical shapeOf the plane reflector must be changed to prohibit radiation in the back and

Side directions .The 90 degree – corner reflector has a unique property , the ray incident on

It reflects exactly in the same direction , so it is not used in military applicationsTo prevent radars from detecting airplanes positions.

97

Types according to geometry Types according to geometry

The most important software used for simulating reflector antennas is “Grasp”.The most important software used for simulating reflector antennas is “Grasp”.

An example for an openGL plot for all

objects of a reflector Antenna using Grasp 9 .

An example for an openGL plot for all

objects of a reflector Antenna using Grasp 9 .

98

5.3.5.3. Types of parabolic surfacesTypes of parabolic surfaces

Parabolic CylinderParabolic Cylinder Parabola Parabola Hyperbola Hyperbola

Focus is a lineFocus is a line Focus is a point Focus is a point

99

5.4. Methods of feeding parabolic reflectors5.4. Methods of feeding parabolic reflectors

Dual offsetDual offsetFront – fed reflectors Front – fed reflectors Offset reflectorsOffset reflectors Cassegrain fedCassegrain fed

100

Methods of feeding parabolic reflectorsMethods of feeding parabolic reflectors

Why we use Offset reflectors ( single and dual ) ? Why we use Offset reflectors ( single and dual ) ?

To avoid blockageavoid blockage caused by struts , we use half a dish and adjust the Feeding element in a way that makes the antenna equivalent to a single

Reflector .

Why we use cassegrain fed reflectors ? Why we use cassegrain fed reflectors ?

This increases the focal length and thus increases the directivity .

101

5.5.Using Image theory in calculating fields5.5.Using Image theory in calculating fields

We use the image theory to find a system of fields but The GTD is more accurate because here we assume

Virtual sources .

2n : number of images , = 180 / n .

= 180 = 90 = 60

102

Using Image theory in calculating fieldsUsing Image theory in calculating fields

E1

E2

E3

E4

En

Total field : E = E1 + E2 + E3 + E4 + ……………….. En

103

5.6 . Using GTD in calculating fields5.6 . Using GTD in calculating fields

Using GTD instead of the image theory results in more accuracyAs we don’t assume virtual sources . The GTD (geometrical Theory of diffraction) accounts for reflection and diffraction of

Rays after calculating the reflection and diffraction coefficients .

104

A satellite dish is a parabolicA satellite dish is a parabolic reflector antennareflector antenna

105

Chapter 6Chapter 6

Microstrip antennas Are considered the

most practical antennasFor mobile communication !

Microstrip antenna

106

MicrostripMicrostrip AntennasAntennas

OutlineOutline

1- Components 1- Components 2- Types of microstrip 2- Types of microstrip

AntennasAntennas3- Feeding techniques3- Feeding techniques

4- Advantages 4- Advantages 5- Disadvantages 5- Disadvantages

6- Techniques to overcome6- Techniques to overcomeDisadvantages Disadvantages

7- Microstrip arrays 7- Microstrip arrays 8- Feeding of arrays 8- Feeding of arrays

9- Microstrip vs. reflectors. 9- Microstrip vs. reflectors.

107

6.1. Components 6.1. Components

A microstrip antenna consists of : A microstrip antenna consists of :

Patch ( radiating Element ) FeedFeed

DielectricDielectric

Ground planeGround planecoppercopper

The patch ( radiating element ) may be circular , rectangular or any other shape . The patch ( radiating element ) may be circular , rectangular or any other shape .

108

Components : Design parameters Components : Design parameters

Design parameters : ( W , L , f , ) , o = c / f , g = / Design parameters : ( W , L , f , ) , o = c / f , g = /

The microstrip antennas have a main radiating edge , the other edge is weaker . The microstrip antennas have a main radiating edge , the other edge is weaker .

W W

L L

109

6.2 . Types of microstrip antennas6.2 . Types of microstrip antennas

Open circuit microstripOpen circuit microstrip Short circuit microstripShort circuit microstrip

-The patch is totally isolatedFrom the ground plane

-Higher efficiency than shortCircuit microstrip antennas .-Side length of the patch is

g / 2.

-The patch is totally isolatedFrom the ground plane

-Higher efficiency than shortCircuit microstrip antennas .-Side length of the patch is

g / 2.

-The patch is connected toThe ground

-Have only one radiating Edge .

- Side length is g / 4 .

-The patch is connected toThe ground

-Have only one radiating Edge .

- Side length is g / 4 .

110

Types of microstrip antennasTypes of microstrip antennas

As it is difficult to manufacture a short circuit microstrip antenna , we use shortingshortingPostsPosts instead .

As it is difficult to manufacture a short circuit microstrip antenna , we use shortingshortingPostsPosts instead .

Shorting posts have :-Inductance in each one

-Capacitance between them > As number of posts increaseResonant frequency increase .

Shorting posts have :-Inductance in each one

-Capacitance between them > As number of posts increaseResonant frequency increase . ShortingShorting

PostsPosts

111

6.3.6.3. Feeding techniques Feeding techniques

Direct feeding by coaxialDirect feeding by coaxialFeed line ( probe ) Feed line ( probe )

Microstrip line Microstrip line Feed Feed

Feeding by coupling Feeding by coupling

ApertureAperture coupledcoupled

feedfeed

Proximity Proximity coupledcoupled

feedfeed

112

Feeding techniques : Feeding techniques : Direct feed by Direct feed by coaxial fees linecoaxial fees line

The inner ( central ) of the coax is attached to the patch while The outer ground is welded to the ground of the microstrip

( like the monopole ) .

The inner ( central ) of the coax is attached to the patch while The outer ground is welded to the ground of the microstrip

( like the monopole ) .

PatchPatch

Coaxial Coaxial

Equivalent circuit Equivalent circuit

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Feeding techniques : Feeding techniques : Microstrip feed lineMicrostrip feed line

It is a conducting strip of much smaller width compared to thePatch , it is easy to fabricate and simple to match ..

It is a conducting strip of much smaller width compared to thePatch , it is easy to fabricate and simple to match ..

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Feeding techniques : Feeding techniques : feeding by couplingfeeding by coupling

ApertureAperture coupledcoupled

feedfeed

Proximity Proximity coupledcoupled

feedfeed

The most difficult to fabricate And has a narrow band ,

Depends on two substrates andA ground with a slot .

The most difficult to fabricate And has a narrow band ,

Depends on two substrates andA ground with a slot .

Has a band width of 13% , however it is difficult to fabricate.

Has a band width of 13% , however it is difficult to fabricate.

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6.4 . Advantages 6.4 . Advantages

1 – 1 – High accuracy in manufacturing , the design is executed byPhoto etching

1 – 1 – High accuracy in manufacturing , the design is executed byPhoto etching

2 – 2 – Easy to integrate with other devices 2 – 2 – Easy to integrate with other devices

3 – 3 – An array of microstrip antennas can be used to form a Pattern that is difficult to synthesize using a single element.

3 – 3 – An array of microstrip antennas can be used to form a Pattern that is difficult to synthesize using a single element.

4 – 4 – We can obtain high directivity using microstrip arrays 4 – 4 – We can obtain high directivity using microstrip arrays

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Advantages Advantages

5 – 5 – Have a main radiating edge , this makes it useful for mobilePhones to avoid radiation inside the device .

5 – 5 – Have a main radiating edge , this makes it useful for mobilePhones to avoid radiation inside the device .

6 – 6 – Small sized applicable for handheld portable communication 6 – 6 – Small sized applicable for handheld portable communication

7 – 7 – Smart antennas when combined with phase shifters . 7 – 7 – Smart antennas when combined with phase shifters .

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6.5 . Disadvantages 6.5 . Disadvantages

4 – 4 – An array suffers presence of feed network decreasing Efficiency , also microstrip antennas are relatively expensive .4 – 4 – An array suffers presence of feed network decreasing Efficiency , also microstrip antennas are relatively expensive .

1 – 1 – Narrow band width ( 1% ) , while mobiles need ( 8% ) 1 – 1 – Narrow band width ( 1% ) , while mobiles need ( 8% )

2 – 2 – Low efficiency , especially for short circuited microstrip antenna

2 – 2 – Low efficiency , especially for short circuited microstrip antenna

3 – 3 – Some feeding techniques like aperture and proximity Coupling are difficult to fabricate

3 – 3 – Some feeding techniques like aperture and proximity Coupling are difficult to fabricate

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6.6 . Techniques for overcoming6.6 . Techniques for overcoming disadvantagesdisadvantages

Conventional techniquesConventional techniques Non conventional techniquesNon conventional techniques

1- Decreasing dielectric Constant

2- Increasing thickness 3- Increasing width .

1- Decreasing dielectric Constant

2- Increasing thickness 3- Increasing width .

1- Aligned parasitic elements2- Using stacked parasitic

Elements.

1- Aligned parasitic elements2- Using stacked parasitic

Elements.

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Techniques for overcomingTechniques for overcoming disadvantages : disadvantages : Aligned parasitic elementsAligned parasitic elements

Feeding one patch by coaxProbe and the other two

Patches are fed by coupling ,This makes the antenna has

Three resonating frequencies And the ultimate resonance

Is of a wider band width.

Feeding one patch by coaxProbe and the other two

Patches are fed by coupling ,This makes the antenna has

Three resonating frequencies And the ultimate resonance

Is of a wider band width.

Patch #1 : Patch #1 : Fed by coax Fed by coax

Feed lineFeed line

Patch #2 , 3 : Patch #2 , 3 : Fed byFed by

Coupling.Coupling.

Single element Single element Parasitic elements Parasitic elements

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Techniques for overcomingTechniques for overcoming disadvantages : disadvantages : Stacked parasitic elementsStacked parasitic elements

Rather than aligning them , We can even combine the two

Methods and modulate the Patch’s shape to yield widest

Band width .

Rather than aligning them , We can even combine the two

Methods and modulate the Patch’s shape to yield widest

Band width .

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6.7 . Microstrip Arrays 6.7 . Microstrip Arrays

2 ^ n2 ^ n

2 ^ n2 ^ n

Feed Network

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Microstrip Arrays Microstrip Arrays

The optimum spacing is 0.8, length must be <= o to avoidMultiple grating lobes and also must be >= lambda / 2 .

The optimum spacing is 0.8, length must be <= o to avoidMultiple grating lobes and also must be >= lambda / 2 .

Advantages of microstrip arrays Advantages of microstrip arrays

1 – 1 – Used to synthesize a required pattern difficult to achieve with A single element.

1 – 1 – Used to synthesize a required pattern difficult to achieve with A single element.

3 – 3 – Increases directivity . 3 – 3 – Increases directivity .

2 – 2 – Used to scan the beam of an antenna system 2 – 2 – Used to scan the beam of an antenna system

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Microstrip Arrays Microstrip Arrays

Disadvantages of microstrip arrays Disadvantages of microstrip arrays

1 – 1 – Narrow bandwidth ( 1 % ) . 1 – 1 – Narrow bandwidth ( 1 % ) .

2 – 2 – Low efficiency 2 – 2 – Low efficiency

3 – 3 – If the separation is more than lambda , grating lobes appear 3 – 3 – If the separation is more than lambda , grating lobes appear

4 – 4 – Feed network decreases efficiency . 4 – 4 – Feed network decreases efficiency .

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6.8 . Feeding of arrays 6.8 . Feeding of arrays

A microstrip antenna uses feed network which may be either : A microstrip antenna uses feed network which may be either :

2 – Corporate feed . 2 – Corporate feed .

1 – Series feed 1 – Series feed

Sometimes feed networks are synthesized with the antenna ! Sometimes feed networks are synthesized with the antenna !

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Feeding of arrays : Series feed Feeding of arrays : Series feed

Series feed Series feed

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Feeding of arrays : Corporate feed Feeding of arrays : Corporate feed

Corporate feed Corporate feed

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6.9 . Microstrip vs. Reflectors 6.9 . Microstrip vs. Reflectors

Preferred for low directivity applications Performed for high directivity

applications as the effect of blockage

Is less

Lower efficiency Higher efficiency

Suffers low efficiency caused by

Feed network for arrays Suffers blockage caused by fixation

Struts

Microstrip AntennasMicrostrip Antennas Reflector Antennas Reflector Antennas

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Microstrip vs. Reflectors Microstrip vs. Reflectors

Smart antennas , uses electronic scanning when combined with phase

Shifters

Uses mechanical scanning .

More accurate manufacturing by

photo etching

Less accuracy , sometimes parabolic

Surfaces are rough

Feeding is by coupling or coax feed

Lines Uses other antenna ( dipole , monopole , apertures , …..etc) as

A feed

Microstrip AntennasMicrostrip Antennas Reflector Antennas Reflector Antennas

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Flat plane Microstrip AntennaFlat plane Microstrip Antenna

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Chapter 7 Chapter 7

Fractal antennas areVery compact as they

Utilize the same Physical area of classicAntennas but with an

Electrically large length !

Fractal antenna

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FractalFractal AntennasAntennas

OutlineOutline

1 – Definition 1 – Definition 2 – Characteristics2 – Characteristics

3 – Types of fractals3 – Types of fractals4 – Advantages 4 – Advantages

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7.1 - Definition7.1 - Definition

A fractal antennafractal antenna is an antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter

(on inside sections or the outer structure), of material that can receive or transmit electromagnetic signals within a given

total surface area or volume. [ source : wikipedia ]

A fractal antennafractal antenna is an antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter

(on inside sections or the outer structure), of material that can receive or transmit electromagnetic signals within a given

total surface area or volume. [ source : wikipedia ]

A fractalfractal is : a recursively generated geometry that has fractional Dimensions.

A fractalfractal is : a recursively generated geometry that has fractional Dimensions.

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Definition : fractal generationDefinition : fractal generation

Some software productscan generate fractals And fractal maps , the Opposite figure shows

A koch loop after severalIterations .

Some software productscan generate fractals And fractal maps , the Opposite figure shows

A koch loop after severalIterations .

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7.2 – Characteristics 7.2 – Characteristics

A fractal antenna's response differs markely from traditional antenna designs, in that it is capable of operating with good-to-excellent performance at many

different frequencies simultaneously. Normally standard antennas have to be "cut" for the frequency for which they are to be used—and thus the standard

antennas only work well at that frequency. This makes the fractal antenna an excellent design for wideband and multiband applications.

A fractal antenna's response differs markely from traditional antenna designs, in that it is capable of operating with good-to-excellent performance at many

different frequencies simultaneously. Normally standard antennas have to be "cut" for the frequency for which they are to be used—and thus the standard

antennas only work well at that frequency. This makes the fractal antenna an excellent design for wideband and multiband applications.

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Characteristics Characteristics

Fractal antennas satisfies the requirements of wireless communication Systems :

Fractal antennas satisfies the requirements of wireless communication Systems :

1 – Wideband 1 – Wideband

2 – Multiband2 – Multiband

3 – Low profile3 – Low profile

4 – Small antenna4 – Small antenna

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The band width of an antenna can be improved as the geometry of theThe antenna best utilizes the available planar area of a circle of radius r

That encloses the antenna .

The band width of an antenna can be improved as the geometry of theThe antenna best utilizes the available planar area of a circle of radius r

That encloses the antenna .

Fractal antennas utilizes the available space in a sphere of radius r in an Efficient way

Fractal antennas utilizes the available space in a sphere of radius r in an Efficient way

The quality factor Q is inversely proportional with the band width.The quality factor Q is inversely proportional with the band width.

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The concept of fractals is frequently used in electromagnetism , and also usedTo represent nature .

The concept of fractals is frequently used in electromagnetism , and also usedTo represent nature .

A Fern fractal Represents a plant

138

7.3 – Types of fractals 7.3 – Types of fractals

Fractals may be:

Deterministic Random

-Von Koch snowflakeVon Koch snowflake- Sierpinski gaskets Sierpinski gaskets - Minkowski island Minkowski island

139

Types of fractals : Koch loop Types of fractals : Koch loop

Fractals that begin with a basic geometry (initiator) and uses a recursiveAlgorithm t produce copies of themselves .

Fractals that begin with a basic geometry (initiator) and uses a recursiveAlgorithm t produce copies of themselves .

Initiator Generator

140

Types of fractals : Koch loop Types of fractals : Koch loop

Iterations Iterations 2 31

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Types of fractals : Minkowski islandTypes of fractals : Minkowski island

A Minkowski islandA Minkowski island A Minkowski island after more iterationsA Minkowski island after more iterationsAs plotted by the directx display of 4nec2As plotted by the directx display of 4nec2

Software ( by Arie voor )Software ( by Arie voor )

142

Types of fractals : Sierpinski gasketsTypes of fractals : Sierpinski gaskets

Determined by the nodes of a Pascal triangle which are numbered by Determined by the nodes of a Pascal triangle which are numbered by the excitation coefficients of the binomial array decided by J.S.stonethe excitation coefficients of the binomial array decided by J.S.stone

( 1 + x ) ^ ( m – 1 ) = 1 + ( m -1 ) * x + ( ( m – 1 ) ( m – 2 ) ( x ^ 2 ) ) / 2! + ( ( m – 1 ) ( m – 2 ) ( m – 3 ) ( x ^ 3 ) ) / 3! +….

( 1 + x ) ^ ( m – 1 ) = 1 + ( m -1 ) * x + ( ( m – 1 ) ( m – 2 ) ( x ^ 2 ) ) / 2! + ( ( m – 1 ) ( m – 2 ) ( m – 3 ) ( x ^ 3 ) ) / 3! +….

1 element1 element2M + 1 = 1

M = 0A1 = 1

2 elements2 elements2M = 2M = 1

A1 = 1 , A2 = 1

3 elements3 elements2M +1 = 3

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The Pascal triangleThe Pascal triangle

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If the nodes with numbers divisible by a prime number p ( p = 2 , 3 , 5 , ………)is deleted the result is a sierpinski gasket of mod-p

If the nodes with numbers divisible by a prime number p ( p = 2 , 3 , 5 , ………)is deleted the result is a sierpinski gasket of mod-p

145

Types of fractals : Random fractalsTypes of fractals : Random fractals

146

7.4 – Advantages 7.4 – Advantages

Fractal antennas results in more compact antennas , but can resonateAnd has input resistance that are much greater than classic geometries

Of loops and dipoles

Fractal antennas results in more compact antennas , but can resonateAnd has input resistance that are much greater than classic geometries

Of loops and dipoles

The first resonance for a linear dipole occurs at lambda / 2 overall lengthWhich can be physically large for some frequencies

The first resonance for a linear dipole occurs at lambda / 2 overall lengthWhich can be physically large for some frequencies

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Advantages Advantages

The higher iterative geometries , the lower resonant frequencies becauseIts overall length becomes electrically large .

The higher iterative geometries , the lower resonant frequencies becauseIts overall length becomes electrically large .

relector antennas

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