Slide 1:1 2008 Fundamental Types of antennas First edition Ahmed M. Alaa


Slide 2:2 F I r s t e d I t I o n Fundamental Types of Antennas By Ahmed M.Alaa


Slide 3:3 Contents Introduction …. 8 Chapter 1 : Basic antenna terminology ………..9 1.1 Radiation pattern 1.2 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


Slide 4:4 Contents Chapter 3 : Loop antennas………..61 3.1 Introduction 3.2 Design Parameters 3.3 Equivalent Circuits 3.4 Loop antenna Configurations 3.5 Applications in mobile Communication system Chapter 4 : Yagi Uda antennas………..77 4.1 Introduction 4.2 Components 4.3 Design procedure 4.4 Advantages 4.5 The folded dipole


Slide 5:5 Contents Chapter 5 : Reflector antennas………..92 5.1 Why Reflectors ? 5.2 Types of reflectors According to geometry 5.3 Types of Parabolic Surfaces 5.4 Methods of feeding Parabolic reflectors 5.5 Using Image theory To calculate field 5.6 Using GTD to calculate The field


Slide 6:6 Contents Chapter 6 : Microstrip antennas………..105 6.1 Components 6.2 Types of microstrip Antennas 6.3 Feeding techniques 6.4 Advantages 6.5 Disadvantages 6.6 Techniques to overcome Disadvantages 6.7 Microstrip arrays 6.8 Feeding of arrays 6.9 Microstrip vs. reflectors.


Slide 7:7 Contents Chapter 7 : Fractal antennas………..130 7.1 Definition 7.2 Characteristics 7.3 Types of fractals 7.4 Advantages


Slide 8:8 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 …


Slide 9:9 Chapter 1 Thomas Edison used Antennas in 1885 ! Basic antenna terminology


Slide 10:10 Basic Antenna terminology Outline 1. Radiation Pattern 2. Directivity 3. Gain 4. Efficiency 5. Types of antennas


Slide 11:11 1.1 Radiation Pattern The distribution of power or it’s Derivatives ( power density , power Intensity ) in the space around the Antenna , relative to the maximum Magnitude , i.e. : Radiation pattern Is concerned with the proportion Of magnitudes and not their values.. The pattern varies according to Different w and u . An example to a radiation pattern in Cartesian coordinates


Slide 12:12 Radiation Pattern An example to a radiation pattern in Polar coordinates u w Azimuth plane Elevation plane


Slide 13:13 Radiation Pattern An example to a 3D Representation of a Radiation pattern.


Slide 14:14 Radiation Pattern : Half power beam width The beam width is the angle included between two angles in which u ( u , w ) Is equal to half Umax , where U is the power intensity . The half power beam Width = u1 - u2 . Where u1 and u2 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


Slide 15:15 Radiation Pattern : Half power beam width When the pattern’s mathematical formula is independent on phi , the pattern Is 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 u = p / 2 , we can calculate Phi 1 and Phi 2 Putting w = p / 2 , we can calculate Theta 1 and Theta 2 Calculating elevation plane beam width


Slide 16:16 Radiation Pattern : Azimuth plane half power beam width


Slide 17:17 Radiation Pattern : Elevation plane half power beam width


Slide 18:18 Radiation Pattern : First Null beam width The beam included by angles where the power is ZERO , usually the first Nulls bound the major lobe of the radiation pattern , the first null beam width Is calculated by estimating the angles where the power intensity is Zero .


Slide 19:19 Radiation 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 .


Slide 20:20 Radiation Pattern : Directive Antennas Side lobes : lobes That have lower Power than major Lobes ( also called Minor lobes ) . Back lobe : The Lobe directed To the earth in 3D representation Major lobes : the Lobes with highest Power concentration ( usually present in Directive antennas) The decart plot of a directive antenna


Slide 21:21 Radiation Pattern : Directive Antennas The 3D plot of a directive antenna


Slide 22:22 Radiation Pattern : Omindirectional Antennas Antennas are said to be omindirectional when the power is distributed Equally around the antenna without being concentrated within a certain Beam .


Slide 23:23 Radiation Pattern : Omindirectional Antennas The decart plot of an omindirectional antenna The distribution of power Around the antenna Is nearly equal .


Slide 24:24 Radiation Pattern : Omindirectional Antennas The 3D plot of an omindirectional antenna


Slide 25:25 1.2 . Directivity Directivity : The measure of how much power , power density or power Intensity 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 .


Slide 26:26 Directivity The directivity is usually inversely proportional with the half power beam width D a ( 1 / HPBW ) U ( u , w ) u U ( u , w ) u Ideal case D = Infinity , and HPBW = 0 . ( a Pulse where ALL Power is concentrating At one point .) Omindirectional


Slide 27:27 1.3 . Gain Gain : The directivity after considering the antennas efficiency . G = D * h Usually measured in dB .


Slide 28:28 1.4 . Efficiency h The Efficiency of an Antenna is divided into three parts : a – Radiation Efficiency b – Mismatch c – Polarization losses .


Slide 29:29 Efficiency : Radiation Efficiency Radiation Efficiency : The efficiency of the antenna itself , regardless of The 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


Slide 30:30 Efficiency : Reflection Mismatch When an antenna is connected to a generator , the transmission line used causes a reflection in the impedance of the antenna if the characteristic impedance of The transmission line ( Zo ) differs from the input impedance of the antenna ( Z in ) . The input impedance is transformed by Zin = ( Zo * Zo ) / Zold . G = | ( Zin – Zo ) / ( Zin + Zo ) | er = 1 - | G | 2 Reflection Coefficient Reflection Efficiency


Slide 31:31 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 to Zin but the transmission Line transforms it according To its characteristic Impedance Zo .


Slide 32:32 Efficiency : Polarization losses If the Polarization of the incident wave is not matching with the polarization of The antenna , losses results in and measured by polarization loss factor PLF . Antenna Polarization Received Signal Cross -Polar Component Co – Polar Component Lost Component c PLF = Cos c


Slide 33:33 1.5 . Types of Antennas 1 – Wire Antennas 3 – Microstrip Antennas 5 – Reflector Antennas 2 – Aperture Antennas 4 – Array Antennas 6 – Lens Antennas .


Slide 34:34 Chapter 2 C.A.Balanis is one of The most important antenna scientists , and Contributed with a famous book “Antenna theory”. Dipole antenna


Slide 35:35 Dipole Antenna Outline 1. Introduction 2. Balanced and Unbalanced Systems 3. Image theory 4. Monopoles 5. Disadvantages Practical Example


Slide 36:36 2.1. 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 considered The 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 l / 4 l / 4 This type of dipoles is called Half wave length dipole as the Total length is lambda / 2 . + -


Slide 37:37 Introduction : Geometry


Slide 38:38 Introduction : dipole configuration


Slide 39:39 Introduction : Characteristics The directivity is nearly equal to 1.6 dimensionless and about 2 -> 2.2 dB , The input impedance is usually 73 + 42.5 j ohms and the radiation resistance Is nearly 73 ohm .


Slide 40:40 Introduction : Radiation Pattern I The dipole is an Electric field Antenna , that means that the magnetic field is Zero 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 .


Slide 41:41 Introduction : Radiation Pattern I The radiation pattern for the Electric field for a folded dipole antenna


Slide 42:42 Introduction : Radiation Pattern II The radiation pattern of the dipole , all the field is electric as shown .


Slide 43:43 The radiation pattern of the dipole , the magnetic field equals zero . No radiation Pattern for the Magnetic field “ H “ !! This means that A dipole is an Electric field Antenna … Introduction : Radiation Pattern III


Slide 44:44 Introduction : 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 lobes where the major Lobes divides into multiple lobes .


Slide 45:45 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 Systems Balanced System Balanced System + - 2 input terminals


Slide 46:46 Balanced 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 have A common ground . Unbalanced System 1 input terminal


Slide 47:47 Balanced and Unbalanced Systems : Baluns


Slide 48:48 2.3 . 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 same Behavior of a dipole but having a single pole , this type of antennas is called Monopoles , and have the advantage of being an unbalanced system . Conductors Fields Electric conductor PEC Magnetic Conductors PMC Electric field Magnetic field


Slide 49:49 Image theory s = infinity s = infinity When electric and magnetic fields are near electric and magnetic fields their Images are in the following directions : PEC PMC


Slide 50:50 2.4 . Monopoles When combining actual and image sources , an equivalent system of a dipole Is 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 is Why monopoles are more practically used than dipoles . A direct ray from the Actual source to the Observation point Represents the first Pole of a dipole . A reflected ray from the Ground plane to the Same observation Point , has the same Effect of a virtual source Representing the second Pole .


Slide 51:51 Monopoles


Slide 52:52 Monopoles Monopole Dipole Zin = 36.5 + 21.25j Zin = 73+ 42.5j


Slide 53:53 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 .


Slide 54:54 Monopoles : Coaxial cables ( Coax ) Co – axial cables consists of a central and a ground plane , it is used to connect The monopole to the load ( ex: a TV ) . Ground plane Central cable Dielectric material


Slide 55:55 Monopoles : Coaxial cables ( Coax ) We benefit from the ground plane of cable by welding it to the ground of monopole And welding it to the ground of monopoles and welding the central cable to the Wire ( the monopole ) . Ground plane Central cable


Slide 56:56 Monopoles : Coaxial cables ( Coax ) We can even make a monopole from just a co – axial cable ! Central cable And the pole of The monopole Antenna at the Same time.. Ground plane Of the monopole And the ground Plane of the coax At the same time.. ~ Equivalent to


Slide 57:57 Monopoles : Baluns When we use a dipole instead of a monopole , we should use a balun , which Is a device that converts a balanced system to an unbalanced system , the Word balun is the abbreviation of “ Balanced to Unbalanced converter “. Balanced System Balun


Slide 58:58 2.5 . Disadvantages An Electric field antenna , this means that the magnetic field “ H “ is Zero at near field , this makes dipoles incompatible with portable Combination . Dipoles are balanced systems , this makes it difficult to mount them On any device without the use of baluns .


Slide 59:59 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 …!!


Slide 60:60 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 e , the length Is reduced then by 1 / e Dielectric cover Material… Antenna with Reduced length .


Slide 61:61 Chapter 3 C.A.Balanis is one of The most important antenna scientists , and Contributed with a famous book “Antenna theory”. Loop antenna


Slide 62:62 Loop Antennas Outline 1. Introduction 2. Design Parameters 3. Equivalent Circuits 4. Loop antenna Configurations 5. Applications in mobile Communication system Practical Example


Slide 63:63 3.1. Introduction As the dipole is the reference ( conventional ) electric field antenna , loops Are the reference magnetic field antenna . Loop antennas can take different shapes Like square , circle , triangle , ellipse or any other closed shape. In dipoles current Moves till discontinuity occurs And then radiates ( Electric field ). When current Circulates in the Loop it is obvious That a magnetic Field is produced. E H i i


Slide 64:64 Introduction : Geometry


Slide 65:65 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 .


Slide 66:66 Introduction : Radiation Pattern The 3D radiation Pattern of loop Antenna , showing The geometry of The loop in blue.


Slide 67:67 Introduction : Radiation Pattern The radiation pattern Of a loop for magnetic Field , the dominant Radiation is magnetic And this is why Loops are magnetic Field antennas .


Slide 68:68 Introduction Types of loops are : Electrically Small Electrically large C < l / 10 C : circumference C ~ l


Slide 69:69 3.2. Design Parameters The radiation resistance of loop antennas is very small and sometimes Less than the loss resistance , this makes them receivers rather than Transmitters where 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 high Permeability ( ferrite loops ).


Slide 70:70 Design Parameters Design parameters : 1 – Perimeter of the loop ( circumference). 3 – Spacing between turns . 2 – Increasing number of turns. 4 – Thickness . 5 – Presence of a ferrite core .


Slide 71:71 Design Parameters The effect of design parameters on added resistance : Ron : Normalized Added resistance. N : Number of turns N = 8 N = 7 N = 6 1.0 1.5 2.0 2.5 3.0 Ron Spacing We seek a design with the Minimum spacing and Maximum turns to satisfy Maximum radiation resistance.


Slide 72:72 Design Parameters Resistance Inductance Capacitance Reactance Resonance occurs When the capacitance And inductance Vanishes and resistance is maximum This is the Area we select the Design within Impedance Thickness to circumference ratio


Slide 73:73 3.3. Equivalent Circuits As we saw the transmitting mode can be modeled by a parallel resonance circuit Transmitting mode Rr Rl Zg Vg + Xa C -


Slide 74:74 Equivalent Circuits Receiving mode Vg Zg Z load + -


Slide 75:75 3.4. Loop Antenna Configurations Top – driven triangular Base – driven triangular Rectangular Circular ~ ~ ~ ~


Slide 76:76 3.5. Loops in mobile communication 1 – Loops are alternative to monopoles , the most widely Used element for hand held portable mobile Communication. 2 – Loops are used in portable pagers , but very few in Transceivers due to high resistance and inductance. 3 – Loops are very immune to noise , having low noise To signal ratio makes them suitable for interfering And fading environment.


Slide 77:77 Chapter 4 The Yagi Antenna is a directional antenna invented by Dr. Hidetsugu Yagi of Tohoku Imperial University and his assistant, Dr. Shintaro Uta. Yagi antenna


Slide 78:78 Yagi – Uda Antennas Outline 1 – Introduction 2 – Components 3 – Design procedure 4 – Advantages 5 – The folded dipole


Slide 79:79 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 element Serving as the feed while the others act as parasitic elements .


Slide 80:80 Introduction This arrangement extends for arrays of loops , an antenna that is very popular Among ham radio operators is the quad antenna . ~ Driven Reflectors


Slide 81:81 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 act as 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 Reflector Directors


Slide 82:82 Components : geometry


Slide 83:83 Components : 3D display


Slide 84:84 4.3 . Design procedure 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 l / 2 ( ~ 0.45 l – 0.49 l ) The directors should be about ( ~ 0.4 l – 0.45 l ) ; less than the feed element


Slide 85:85 Design 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 gain Independent 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 !


Slide 86:86 Design procedure Most antennas has from 6 to 12 directors . The separation between the feed element and the reflector is less than that of The feed and the nearest director ( nearly 0.25 lambda )


Slide 87:87 Design procedure The 3D radiation pattern


Slide 88:88 Design procedure The 2D radiation pattern


Slide 89:89 Design procedure The SWR plot of the yagi uda


Slide 90:90 4.4 . Advantages Light weighted Simple to build Low cost .


Slide 91:91 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 .


Slide 92:92 Chapter 5 The first cassegrain Reflector was designed By Laurent cassegrain In 1672 . Reflector antenna


Slide 93:93 Reflector Antennas Outline 1- Why Reflectors ? 2 – Types of reflectors According to geometry 3 – Types of Parabolic Surfaces 4 – Methods of feeding Parabolic reflectors 5 – Using Image theory To calculate field 6 – Using GTD to calculate The field


Slide 94:94 5.1. Why Reflectors ? While using aperture antennas we always need to increase the aperture Area to increase its directivity ,but as this is not practical , instead of using Large apertures we place a reflecting surface face to face with the aperture ( or any other antenna ) , the reflecting surface collimates radiation to The small aperture and thus we satisfied high directivity with a small Aperture , and overcame space limitations. A side view of An aperture of A large area A side view of An aperture of A small area And a reflecting Surface used.


Slide 95:95 5.2. Types according to geometry Plane reflectors Corner reflectors Curved reflectors


Slide 96:96 Types according to geometry : 90 degree corner To better collimate the energy in the forward direction , the geometrical shape Of 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 applications To prevent radars from detecting airplanes positions.


Slide 97:97 Types according to geometry 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 .


Slide 98:98 5.3. Types of parabolic surfaces Parabolic Cylinder Parabola Hyperbola Focus is a line Focus is a point


Slide 99:99 5.4. Methods of feeding parabolic reflectors Dual offset Front – fed reflectors Offset reflectors Cassegrain fed


Slide 100:100 Methods of feeding parabolic reflectors Why we use Offset reflectors ( single and dual ) ? To avoid 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 ? This increases the focal length and thus increases the directivity .


Slide 101:101 5.5.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 , c = 180 / n . C = 180 C = 90 C = 60


Slide 102:102 Using Image theory in calculating fields E1 E2 E3 E4 En Total field : E = E1 + E2 + E3 + E4 + ……………….. En


Slide 103:103 5.6 . Using GTD in calculating fields Using GTD instead of the image theory results in more accuracy As 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 .


Slide 104:104 A satellite dish is a parabolic reflector antenna


Slide 105:105 Chapter 6 Microstrip antennas Are considered the most practical antennas For mobile communication ! Microstrip antenna


Slide 106:106 Microstrip Antennas Outline 1- Components 2- Types of microstrip Antennas 3- Feeding techniques 4- Advantages 5- Disadvantages 6- Techniques to overcome Disadvantages 7- Microstrip arrays 8- Feeding of arrays 9- Microstrip vs. reflectors.


Slide 107:107 6.1. Components A microstrip antenna consists of : Patch ( radiating Element ) Feed Dielectric Ground plane copper The patch ( radiating element ) may be circular , rectangular or any other shape .


Slide 108:108 Components : Design parameters Design parameters : ( W , L , f , e ) , lo = c / f , lg = l / e The microstrip antennas have a main radiating edge , the other edge is weaker . e W L


Slide 109:109 6.2 . Types of microstrip antennas Open circuit microstrip Short circuit microstrip The patch is totally isolated From the ground plane Higher efficiency than short Circuit microstrip antennas . Side length of the patch is lg / 2. The patch is connected to The ground Have only one radiating Edge . - Side length is lg / 4 .


Slide 110:110 Types of microstrip antennas As it is difficult to manufacture a short circuit microstrip antenna , we use shorting Posts instead . Shorting posts have : Inductance in each one Capacitance between them > As number of posts increase Resonant frequency increase . Shorting Posts


Slide 111:111 6.3. Feeding techniques Direct feeding by coaxial Feed line ( probe ) Microstrip line Feed Feeding by coupling Aperture coupled feed Proximity coupled feed 1 2 3


Slide 112:112 Feeding techniques : Direct feed by coaxial 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 ) . Patch Coaxial Equivalent circuit


Slide 113:113 Feeding techniques : Microstrip feed line It is a conducting strip of much smaller width compared to the Patch , it is easy to fabricate and simple to match ..


Slide 114:114 Feeding techniques : feeding by coupling Aperture coupled feed Proximity coupled feed The most difficult to fabricate And has a narrow band , Depends on two substrates and A ground with a slot . Has a band width of 13% , however it is difficult to fabricate.


Slide 115:115 6.4 . Advantages 1 – High accuracy in manufacturing , the design is executed by Photo etching 2 – Easy to integrate with other devices 3 – An array of microstrip antennas can be used to form a Pattern that is difficult to synthesize using a single element. 4 – We can obtain high directivity using microstrip arrays


Slide 116:116 Advantages 5 – Have a main radiating edge , this makes it useful for mobile Phones to avoid radiation inside the device . 6 – Small sized applicable for handheld portable communication 7 – Smart antennas when combined with phase shifters .


Slide 117:117 6.5 . Disadvantages 4 – An array suffers presence of feed network decreasing Efficiency , also microstrip antennas are relatively expensive . 1 – Narrow band width ( 1% ) , while mobiles need ( 8% ) 2 – Low efficiency , especially for short circuited microstrip antenna 3 – Some feeding techniques like aperture and proximity Coupling are difficult to fabricate


Slide 118:118 6.6 . Techniques for overcoming disadvantages Conventional techniques Non conventional techniques 1- Decreasing dielectric Constant 2- Increasing thickness 3- Increasing width . 1- Aligned parasitic elements 2- Using stacked parasitic Elements.


Slide 119:119 Techniques for overcoming disadvantages : Aligned parasitic elements Feeding one patch by coax Probe 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 : Fed by coax Feed line Patch #2 , 3 : Fed by Coupling. Single element Parasitic elements


Slide 120:120 Techniques for overcoming disadvantages : Stacked parasitic elements Rather than aligning them , We can even combine the two Methods and modulate the Patch’s shape to yield widest Band width .


Slide 121:121 6.7 . Microstrip Arrays 2 ^ n 2 ^ n Feed Network


Slide 122:122 Microstrip Arrays The optimum spacing is 0.8lo , length must be = lambda / 2 . Advantages of microstrip arrays 1 – Used to synthesize a required pattern difficult to achieve with A single element. 3 – Increases directivity . 2 – Used to scan the beam of an antenna system


Slide 123:123 Microstrip Arrays Disadvantages of microstrip arrays 1 – Narrow bandwidth ( 1 % ) . 2 – Low efficiency 3 – If the separation is more than lambda , grating lobes appear 4 – Feed network decreases efficiency .


Slide 124:124 6.8 . Feeding of arrays A microstrip antenna uses feed network which may be either : 2 – Corporate feed . 1 – Series feed Sometimes feed networks are synthesized with the antenna !


Slide 125:125 Feeding of arrays : Series feed Series feed


Slide 126:126 Feeding of arrays : Corporate feed Corporate feed


Slide 127:127 6.9 . Microstrip vs. Reflectors Microstrip Antennas Reflector Antennas


Slide 128:128 Microstrip vs. Reflectors Microstrip Antennas Reflector Antennas


Slide 129:129 Flat plane Microstrip Antenna


Slide 130:130 Chapter 7 Fractal antennas are Very compact as they Utilize the same Physical area of classic Antennas but with an Electrically large length ! Fractal antenna


Slide 131:131 Fractal Antennas Outline 1 – Definition 2 – Characteristics 3 – Types of fractals 4 – Advantages


Slide 132:132 7.1 - Definition A fractal 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 is : a recursively generated geometry that has fractional Dimensions.


Slide 133:133 Definition : fractal generation Some software products can generate fractals And fractal maps , the Opposite figure shows A koch loop after several Iterations .


Slide 134:134 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.


Slide 135:135 Characteristics Fractal antennas satisfies the requirements of wireless communication Systems : 1 – Wideband 2 – Multiband 3 – Low profile 4 – Small antenna


Slide 136:136 Characteristics The band width of an antenna can be improved as the geometry of the The 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 The quality factor Q is inversely proportional with the band width.


Slide 137:137 Characteristics The concept of fractals is frequently used in electromagnetism , and also used To represent nature . A Fern fractal Represents a plant


Slide 138:138 7.3 – Types of fractals Fractals may be: Deterministic Random Von Koch snowflake Sierpinski gaskets Minkowski island


Slide 139:139 Types of fractals : Koch loop Fractals that begin with a basic geometry (initiator) and uses a recursive Algorithm t produce copies of themselves . Initiator Generator


Slide 140:140 Types of fractals : Koch loop Iterations 2 3 1


Slide 141:141 Types of fractals : Minkowski island A Minkowski island A Minkowski island after more iterations As plotted by the directx display of 4nec2 Software ( by Arie voor )


Slide 142:142 Types of fractals : Sierpinski gaskets Determined by the nodes of a Pascal triangle which are numbered by the 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 element 2M + 1 = 1 M = 0 A1 = 1 2 elements 2M = 2 M = 1 A1 = 1 , A2 = 1 3 elements 2M +1 = 3


Slide 143:143 Types of fractals : Sierpinski gaskets The Pascal triangle 1 1 1 1 2 1 1 3 3 1 1 4 6 4 1 m=1 m=2 m=3 m=4 m=5


Slide 144:144 Types of fractals : Sierpinski gaskets 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


Slide 145:145 Types of fractals : Random fractals


Slide 146:146 7.4 – Advantages Fractal antennas results in more compact antennas , but can resonate And 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 length Which can be physically large for some frequencies


Slide 147:147 Advantages The higher iterative geometries , the lower resonant frequencies because Its overall length becomes electrically large .