CHAPTER -1 INTRODUCTION The antenna was first invented by Marconi in 1906 and his work provided an aisle for many forthcoming developments up to date in the stream of communication and he also drafted a law which is popularly known as Marconi law and it states that the maximum distance of separation depends on the square of the height of the antenna

CHAPTER -1
INTRODUCTION

The antenna was first invented by Marconi in 1906 and his work provided an aisle for many forthcoming developments up to date in the stream of communication and he also drafted a law which is popularly known as Marconi law and it states that the maximum distance of separation depends on the square of the height of the antenna. Antennas are generally used to radiate energy into space from source to the destination and till today there are many developments in the antennas to meet the demands of the present day technology and all the developments in the antennas mainly depends upon varying different parameters of the antennas and antennas are used in every communication system and in many applications the major design constraint is the size of the antenna so many new techniques are being used for reducing antenna size.

Fig 1.1.1 Marconi antenna
Antennas are used to scatter energy into space from the source to the destination and till today there are many developments in the antennas to meet the requirements till the present day technology and all the developments in the antennas mainly depends upon fluctuating different parameters of the antennas and antennas are used in almost each and every communication system and in many applications. The major design constraint is the size of the antenna so many modern techniques are being used to scale down the size of the antenna. Antennas are mainly used for the propagation of waves in the electromagnetic region. In late 19th century, antennas came into existence, at that time there are only very less number of antennas in the world. From the time of Second World War, antennas have been used widely due to their vast applications. From the beginning of the 21st century antennas are being started to use in mobile phones. When the GPS is activated in the mobile phone then it represents everyone is carrying an antenna. Antennas are widely used in wireless communications. Generally the antenna can transmitter or a receiver. Transmitter will supply the power at radio frequency, while the receiver receives the power and generates voltage across receiver. Antenna is used in many of wireless applications. Antenna used in the satellite communication is the dish antenna. These dish antennas are operating at only microwave frequencies.

1.1 Antenna Parameters:
Generally, antenna characteristics can be determined by its parameters such as radiation pattern, beam width, radiation, power density, radiation intensity, directivity, efficiency, gain and polarization
1.1.1 Beam Width:
The average performance of an antenna reduces when it radiates in undesirable directions because of the number of side lobes. In war zones if the opponent is going to targeting another one,the beam width is an important factor which makes a difference between the sources within that neighbourhood. The beam width is often expressed as
• First null beam width
• Half power beam width
• First side lobe half power beam width
• Second major side lobe beam width

1.1.2 Efficiency:
Suppose if the transmitting antenna radiates certain amount of power and if the receiving antenna captured power is equals to power transmitted, then antenna is said to be perfect aperture generally it is defined as the ratio of the aperture area and its physical area.
?R=Pradiated/Pinput
1.1.3 Radiation pattern:
Radiation pattern depicts the radiation capability of a particular antenna with respect to the space coordinates and it is the main parameter by which a user can adopt that particular antenna to meet the present needs and it is generally used to describe the behavior of the antenna in the far field region.

1.1.4 Directivity:
Generally, an isotropic radiator radiates the power in equal amount in all the directions and the directivity is defined as “the ratio of the power density radiated by the transmitting antenna or the antenna under test to the power density radiated by the isotropic radiator”.
D(?,?)=U(?,?)/Uavg=4? U(?,?)/Prad

1.1.5 Power Density:
Every parameter of the antenna is generally measured at the far field and the power pattern is obtained by having the average power density radiated by that antenna as a function of the direction. Observations are made over a sphere of constant radius extends into the far field.
P=E x H

Fig 1.1.2 Sphere of finite radius
1.1.6 Gain of the antenna:
The gain of the antenna under test or transmitting antenna is much similar to the directivity of the antenna. Directivity deals with the directional abilities of that particular antenna whereas the gain also deals with the efficiency in addition to the directional abilities of the antenna and impedance mismatches and polarization losses are not considered into account while gain is obtained for the given antenna. The gain is a dimensionless quantity.
G(?,?)=U(?,?)/(Pin/4? )=4? U(?,?)/Pin
1.1.7 Polarization:
Polarization gives the direction of the instantaneous electric field. Generally polarization is divided into linear, circular or elliptical. If the electric field at a particular point is along a straight line, then it is called as linear polarization and elliptical polarization and circular polarization are cases of the elliptical polarization. If the instantaneous electric field traces an ellipse, then it is known as elliptical polarization. Polarization can be clockwise or anticlockwise and the field must be observed in the direction in which the energy is propagating.

Fig:1.1.3 Polarization
1.1.7.1 Linear polarization:
The linear polarization can be expressed as polarization of electromagnetic wave remains in the same direction, whenever the vector is placed at the fixed point, although there is a change in magnitude. Generally there are two types of linear polarization.One is the vertical polarization, whenever the electric field is perpendicular to the ground then it is called as vertical polarization

Fig.1.1.4 Horizontal linear polarization
. The other one is when the electric field is along the earth’s surface then is called horizontal polarization. We can consider the linear polarization whenever the equipment is of low cost.

Fig 1.1.5Vertical linear polarization
1.1.7.2 Circular polarization:
In circular polarization, the polarization plane will be in a rotating manner. The plane will complete its full revolution for each wavelength. Similar to the linear polarization, circular polarization will also cover vertical and horizontal planes during the polarization.

Fig 1.1.6 Circular polarization
There are two types of circular polarization one of them is Right Hand Circular (RHC) polarization. It monitors a clockwise pattern, and LeftHand Circular (LHC) polarization which monitors a anti clockwisepattern.
1.1.8 Voltage standing wave ratio:
These are considered to be the factors for maximum power transfer between the transmitter and receiver and therefore the antenna should perform efficiently. This happens only if the ohmic resistance Zin is matched to the transmitter ohms resistance, Zs.
1.1.9 Return loss:
The return loss can be calculated by using Scattering Parameters (S11 and S22).This is the simplest and user friendly methodology to calculate the input signal and output signal of the given sources. It may be same that once the load is not matched the full power is not obtained by the load, there is a charm of the facility which is named loss, and the loss that comes back is the Return loss.
RL=10log(PR/PI)
The return loss is given by:
Pi is the power from the source and Pr is force reflected. In the event that Vi is the plentifulness of the episode wave and Vr the reflected wave, then the arrival misfortune can be communicated as far as the reflection coefficient ? as:
RL=-20log(?)
For a reception apparatus to emanate viably, the arrival misfortune ought to be less than?10 ??.

1.2 Antenna Types:
1.2.1 Patch Antenna
A patch receiving wire is a narrow band, wide reception apparatus obtained by carving the radio wire component design in metal follows attached to a dielectric substrate which protects. Normal micro strip receiving wire shapes are rectangle or square, roundabout and curved, yet any constant shape is conceivable. Some patch radio wires don’t utilize a dielectric substrate and rather made of a metal patch mounted over a ground plane utilizing dielectric spacers; the subsequent structure is less tough yet has a wider bandwidth. Since such reception apparatuses have a position of safety, are mechanically rough and can be molded to adjust to the bending skin of a vehicle, they are regularly mounted on the outside of air ship and the shuttle, or are consolidated into portable radio specialized gadgets.
1.2.2 Microstrip Antenna:
A Micro-strip patch radio wire comprises of an emanating patch on one side of a dielectric substrate which has a ground plane on the other side. Also known as “Printed Antennas”. A micro strip Antenna (Application particular Antenna) is a directional receiving wire, which transmit more power in some specific headings than the others. The directivity is diverse in various bearings.

Fig 1.2.1 Shapes of patches
1.2.2.1 Features of Rectangular Patch Antenna:
• The basic form of rectangular patch antenna consists of a radiating patch on one side of a dielectric substrate which has a ground plane on the other side.
• The patch is generally made of conducting material such as copper or gold and can take any possible shape.
• The radiating patch and feed lines are usually photo etched on the dielectric substrate.
• The thickness of the patch is very thin compared to the free space wavelength.
• Permittivity range should be in between 1.2 to 2.2.

1.2.2.2 Features of circular patch antenna:
• Resonates at dual frequencies.
• When the substrate thickness changes the resonant frequency and antenna parameters are changed.
• Gain increases and then decreases with the increase in the thickness.
• The radiation efficiency increases and then decreases with the increase in the thickness.
• Peak gain increases and then decreases with the increase in the thickness.
• Peak directivity also first increases and then decreases with the increase in the thickness.
• Stability is more in circular patch antenna.

1.2.3 Monopole antenna:
It is a radio antenna in which a conductor of rod shape is mounted perpendicularly on a conducting surface called as called ground plane. Basically monopole antenna is known as resonating antenna as its characteristics are depending on the length. So for this case we need to know the length of the antenna and there are methods to find length of antenna. One method is it can be measured by using the wavelength of radio waves that the antenna has been using. The fundamental form of monopole antenna is quarter-wave monopole in which its length is ¼ of the radio waves wavelength it has been using A monopole antenna can be viewed as unlike the dipole antenna here the bottom half of vertical dipole is replaced by conducting plane i.e ground plane at right angles to the remaining half. There are many types of monopole antennas in which ground plane used may be actual earth or any other. When multiple antennas are used for controlling the direction of radiation frequency propagation, then those antennas are called directional antenna arrays. The radiation example of monopole radio wires over a ground plane are additionally known from the dipole result.
1.2.4 Spiral antenna:
Spiral antennas are well known for their wide band usage. These are travelling wave structures, in these antennas stability in input impedance can be achieved easily. Spiral antennas have very small structure due to reducing size with its windings. Broadband performance are allowed by travelling wave which is formed on spiral arms, fast wave is formed due to mutual coupling phenomenon occurring between arms of spiral. Working principle of spiral antenna is explained by ring theory which is also known as band theory which states that the antenna radiates active region spiral have equal wavelength. Normally we can obtain different designs of spiral antennas by just changing the no of turns and width of arms. Dielectric substrates like Rogers RT Duroid are used. Here the direction of theantenna polarization depends on the direction of the rotation of spiral and additional spirals also can be included to make multi-spiral structure. This spiral has a cavity which may be a vacuum or of air or conductive material where it manipulates the antenna pattern to a unidirectional shape. One of the applications of spiral antennas includes wideband applications and monitoring frequency spectrum.

Fig 1.2.2 Spiral antenna
Generally pair of spiral antennas of identical parameters except polarization is used in some applications which come under above mentioned. These are also used in microwave direction finding.
1.2.5 Slot Antenna:
An example for aperture antenna is a slot antenna. These slots can be of different shapes and sizes. They are fabricated on a conducting sheet. These slot antennas can be fabricated by making a cut on the surfaces where they are mounted.

Fig 1.2.3Slot antenna
The working and analysis of a slot antenna can be clearly explained with the aid of Babinets principle. This principle is related to optics, but can be used in the analysis of a slot antenna. When an infinite conducting sheet is supplied with cots and excited with a high field, a radiation of the field is observed. It involves a cut in a screen and a complementary pair of screen. It states that when a field behind a screen with an opening is added to a field of a structure complementary to it, it is equal to the field when the screen is absent, that means the overall effect of the screen is nullified.
1.2.6 Array Antenna:
A collection of similar or different kinds of elements is known as an array. Antenna arrays are a collection of different or the same kind of antennas grouped together to work for the specified parameters. The parameters specified are generally the directional characteristics. Antenna arrays are an assembly of radiating elements in a specified electrical and geometrical configuration. In general all the elements are identical. The controls can be as follows:
• Geometrical arrangement
• Spacing between elements
• Excitation amplitude
• Excitation phase
• Element pattern
1.2.6.1 Broad Side Array:
If the direction of maximum is along ?=90 degrees, then it is called a broadside array.
To have the maximum direction along ?=90 degrees, we require
• Element pattern having maximum along ?=90 degrees.
• Array factor having maximum along ?=90 degrees.
1.2.6.2 End Fire Array:
If the direction of maximum radiation is either along ?=0 or 180 degreesthen it is called end fire array.

Fig 1.2.4 Field patterns of end fire and broad side arrays

1.3 Antenna Working:
Generally, an antenna is a structure that radiates the information that is to be transmitted from the transmitter to the receiver in the form of electromagnetic waves which can be propagated in the free space and an antenna is made up of metal which contains the electrons that can be excited when the antenna is fed with a voltage then according to the universal truth that electric field is present with the charged particles.

Fig1.3.1 Electric field around the negative charge
Electric field is a vector quantity that implies that it contains both direction and magnitude and if the voltage is applied then the particle travels with a constant velocity and then the electric field gets disturbed.

1.4 Feeding Techniques:
There are different types of feeding techniques used to design an antenna co-axial cable feed coupled feed ,aperture feed ,micro strip feed etc. We can analyze the results of the antenna depending on the feeding technique. There are numerous arrangements that can be utilized to sustain microstrip antennas. Microstrip reception apparatuses are moderately economical to make and plan as a result of the basic two-dimensional physical geometry. They are used normally at Ultra High Frequencies and at higher frequencies in light of the fact that the span of the receiving wire is straightforwardly addicted to the wavelength at the thunderous recurrence. utilizes lithographic methods. The patch clusters may give much higher increases than a A solitary patch receiving wire shows a most extreme order increase of around 6-9 db. It is moderately simple to print a variety of patches on a solitary (extensive) substrate which solitary patch at least extra cost; coordinating and stage conformity can be performed with printed microstrip sustain structures, again in the same operations that shape the emanating patches. The capacity to make high pick up clusters in a position of safety radio wire is one reason that fix exhibits are basic on planes and in other military applications.
1.4.1 Co-Axial Cable Feed:
One of the most common techniques used for the design of any antenna is co-axial feed technique. In this type of feeding technique the patch is placed at the top of the substrate and at the bottom of the substrate ground plane is attached. This type of technique uses a connector called co-axial connector which is passed through the ground plane and is attached to the patch antenna. There are having some advantages by using this technique like inside the patch the feed can be placed at any position so it corresponds with its input impedance. It also offers some disadvantages like it offers narrow bandwidth, to connect with the patch a hole must be made so it increase some complexity. Its bandwidth ranges in between 2-5%. It has poor reliability when compared with the other feeding techniques.

Fig:1.4.1 Coaxial feed
1.4.2 Coupled Feed:
This is considered as indirect feed technique as it will not touch the antenna directly. It also offers some advantages like as it is not directly touching the antenna there should be some gap between the feed and the patch and this gap will produces some capacitance which will not allow the inductance to be entered into the feed. Its bandwidth ranges in between 2-5%. It is having good reliability compared to other feeding techniques.
1.4.3 Aperture Feed:
This is the one of the feeding techniques that is used to design an antenna. In this type of feeding technique the patch antenna which is radiating and the feed that is used is separated by the ground plane and by using a slot coupling between them takes place. The slot that is responsible for coupling is placed at the center position and the amount of coupling that takes place will depends on some parameters like size, shape, position. In this type of feeding techniques radiation is less compared to the other feeding techniques as both the patch and the feed is separated by a ground plane, as the layers are increasing one by one in becomes complex to design this is the main disadvantage in this type of feeding technique. It is having bandwidth in the order of 2-5%. It is having good reliability compared to other feeding techniques.

Fig: 1.4.2 Aperture coupled feed
1.4.4 Micro-strip Line Feed:
In this type of feeding technique a strip which is conducting is placed at one of the edges of the patch antenna.

Fig: 1.4.3 Strip-line feed
It also offers some advantages over other feeding techniques like the feed that is attached to the patch antenna can be removed to obtain some other form of structures for example: planar structure and comparing the patch and the strip that is conducting the strip is very small in terms of width. This type of feeding technique is very easy to fabricate compared to other feeding techniques. Its bandwidth ranges in between 2-5%. It has better reliability compared to other feeding techniques.
1.4.5 Proximity Coupled Feed:
Proximity coupled feed is also called as near coupling or electro magnetical coupling scheme. Two dielectric substrates are used and a feed line is in between substrates and a radiating patch is on the upper substrate. The advantage of proximity coupled feed is it eliminates spurious oscillations, provides high bandwidth and helps in the optimization of individual performances. The main disadvantage is it is very difficult to fabricate due to presence of two layers and it requires proper alignment and arrangement and the thickness is more.

Fig:1.4.4 Proximity coupled feed

CHAPTER 2
LITERATURE REVIEW

2.1Statement of purpose:
The design of particular antenna gives description for the use of UWB applications by using meta-materials for fabrication under required cut off frequencies. It also provides solution for how the antenna works under specific frequency for the gain improvements. The overview of this paper describes the use of VIVALDI antenna for UWB applications using metamaterials and unit layout techniques. By using metamaterial unit layouts the transmission characteristics of tapered slot antennas are analyzed.

2.2 Literature Survey:
These days, scientists in the field of remote correspondence have concentrated their exploration on the artificial materials which could be connected in 4G portable correspondence, 4G applications, Bluetooth framework etc., Various researches have contributed to enhance this design. First the different techniques for design of tapered slot antennas are studied. But achieving linearity phase center with tapered slot antenna is difficult. Wideband circularly polarized curved antipodal slot antennas were studied. These can also be used for 5G applications but the gain obtained is in the range of 8dcib. So gain improvement techniques are necessary to enhance the standard of this design. One of the approaches is air filled antipodal linear slot antenna but this was useful only in Ka band of frequency. Another approach was using LCP substrate.
A better gain improvement was observed. But liquid crystal polymer is very costly to implement and they can’t tolerate damages and they are useful only in E and W bands. So other approaches are to be analyzed to improve gain at resonant frequencies with less cost. One of the solutions presented here is the use of metamaterial unit layouts which are cost efficient and are easy to implement. They have negative refractive index. A basic Vivaldi antenna is designed with an end-fire pattern and the tapered slot antennas are used to improve the pattern in end-fire direction.
Balanced antipodal Vivaldi antenna using strip-line technology is designed having linear polarization. The operating band is observed to be UWB (1.3-20GHz) with references to 10 dB impedances and the cross-polarization level is observed to be less than -17 dB 1. Vivaldi antennas can be designed on different kinds of substrates depending on the operating bands they serve and the preferred requirements.
Reference 2 demonstrates the Vivaldi antennas on FR4 and RO3006 and comparisons between them. FR4 is more advantageous as it can be easily integrated with circuits. As the antennas proposed here are not showing the gain of 10- 15 dB they can be used in mobile electronics consuming low power and short-range applications. Pulse response as low as 1ns can be designed on Rogers RT6010LM which operates in the UWB band. Front to back ratio greater than 16 dB with resultant peak gain of 10.2 dBi is designed this is suitable to use in imaging and precision ranging applications 3.
Vivaldi notch antennas are end fire radiators and can be of two types namely single and dual polarized radiators. A single notch antenna with a triangular lattice structure avoiding the formation of grating lobes. Wide angle scanning along with suitable cross polarization levels over wide band is observed 4. Bandwidth of Vivaldi antenna can be improved with a higher range of about 40 GHz. This can be accomplished by modifying the loading structure to match load. Circular shaped load and slot load are proposed and a performance up to 46 GHz is observed. The Vivaldi antenna loaded with circular shape is observed to have low return loss and antenna loaded with slot structure shows 2 GHz wider bandwidth and return loss Save As or pressing Ctrl+S shortcut. We can open already saved project using the File-;Open command or pressing Ctrl+O shortcut.

Fig 4.1.1 Flow chart of HFSS design
4.1.2 Insert an HFSS design into a project:
1) On the menu bar opt Project, opt Insert HFSS Design from the dropbox.
2) The new design option appears in the project dropbox.
3) It is named as HFSS Design by default in the system, and m is the order in which the design is being involved in the project. The 3D modeler menu appears to right of the Project Manager on the menu bar. You can create the geometry of the required model as per the specifications.

Fig 4.1.2 Inserting HFSS design into project

Before you are drawing the model, do specify the design’s solution type.
1) On the menu bar select HFSS menu, click on Solution type in the dropbox. The solution type dialogue box can be seen

Fig 4.1.3 Specifying solution type
2)Opt the Driven Model option in the listed solution types.
We generally opt the Driven Model as our design to be done is a waveguide and driven model is the best option for it and mode based S parameters of the passive, high-frequency structures such as waveguides and micro-strip patches which are mainly driven by the sources.
You can then opt to show the modals dimensions in the selected new units or we can rescale the modals dimensions to the selected new units.
4.1.3 To select the model’s measurement units:
1) On the menu bar opt 3D modeler menu, select units. The Set Model Unit dialog box pops up.
2) Opt the new unit model from the Select Unit’s pull down tree.

Fig 4.1.4 Selecting model units
3) You can change the size of the design by opting the rescale to new unit option to rescale the already used dimensions to the required new units. Unselect the rescale to new unit option to convert the dimensions to the required new units without making any changes in their scale.
4) Opt the Ok option to save the changes.
4.1.4 To Draw a model:
You can easily draw 3D objects by using the HFSS Draw commands. Objects are designed and shaped in the 3D modeler window.
To draw a waveguide rectangular in shape,
1) On the menu bar opt the HFSS option, opt the Draw. The Draw dialog box pops up. As we need to draw a cuboid opt the Box option.

Fig 4.1.5 Drawing a box
2) Then draw the box and change the dimensions in the create box option. We can also change the co-ordinates of the box.
4.1.5 To Assign the Materials:
1) Firstly, Right click the mouse on the 3D modeler Window from the menu bar to get the 3D Modeller dropbox.
2) On the 3D Modeler drop box opt the assign material option.
3) The Select Definiton drop box pops up. Default in the system the entire list of materials in global library of materials available in Ansoft is displayed and we can assign material of our choice.
4) Select air or vaccum for the box.
5) Opt OK
6) The material of your choice is allocated to the object.

Fig 4.1.6 Selecting faces

Fig 4.1.7 Assigning material

4.1.6 Assigning Boundaries:
The Boundary conditions state the behavior of the field at the abyss of the problem region and object interfaces.
1) Firstly Right click with the mouse on the 3D modeler window from menu bar to optfaces.
2) Opt on the faces option to assign which faces are to be allocated to be a perfect conductor.

Fig 4.1.8 Assigning boundaries

Fig 4.1.9 Assigning finite conductivity to box
3) On the menu bar select HFSS menu, opt the Boundaries, choose assign Boundary and opt finite Conductivity.
4.1.7 Assigning excitations:
The Excitations in HFSS design is utilized to specify the sources of electromagnetic fields and surges, currents, voltages in surfaces or objects in the design.
Assigning excitations requires 2 steps:
i) Assigning Ports
ii) Assign the Integration Lines or the Terminal lines discretely for each and every mode.
i)To Assign ports:
1) Opt the object face to which you want to assign the port.
2) Choose HFSS->Assign-> Wave port. The Wave port entitles the surface from which the signals enter or leave the geometry. Hence the 2 ports are required to be given definitions. HFSS makes an assumption that each Wave Port which we are defining is in connection to a semi infinetely long waveguide which is having the same type of cross section and the same material properties as that of the port. The HFSS derives the solutions from the wave ports by exciting them individually.

Fig 4.1.10 Assigning ports
3) The option named wave-port pops up when we select assign excitation option.
4) Give the port a name of your own choice in the Name text box or simply give the default name and then opt next.
5) To specify more number of modes, type a required value in the New number of modes dropbox and choose the update option. The new modes spreadsheet is now changed with the new values.

Fig 4.1.11 Assigning multi modes

4.1.8Solution setup:
Go to the solution set up and add set up

Fig 4.1.12 Adding set up to the solution
4.1.9To validate HFSS design

Fig 4.1.13 Validating the design
4.1.10To analyze the design
1) On the HFSS menu, click Analyze

Fig 4.1.14 Analysis of design
Whenever a simulation is running, you can keep a check on the solution’ in the Progress window

Fig 4.1.15 Simulation running on local machine
You can also view the data in the solution setup being run at any point of time.
Convergence the data- by choosing HFSS-;Analysis Setup-;Convergence.
Matrices computed for the S-parameters, impedances, and propagation constants can be viewed by clicking HFSS;Analysis Setup;Profile.
4.2 Design:
The design procedure for the antenna was analyzed in an iterative procedure starting from Vivaldi antenna and then increasing the unit cells based on the requirements and the performance of the antennas. The top side and flip side are shown in blue and red colors simultaneously. Vivaldi antenna has many applications in ultra wide band. The dimensions of antennas can be changed and used accordingly at different frequencies.

Fig 4.2.1 Iteration 1 (Vivaldi Antenna)
A metamaterial inspired Vivaldi antenna of size 72mm*42mm etched on a FR4 substrate having dielectric constant of 4.4 and loss tangent of 0.02 has been proposed as shown in figure 4.2.1. The proposed antenna demonstrated has a thickness of 1.6mm. Iteration one of the antenna is the basic Vivaldi antenna which works in the range of ultra wide band (3.1GHz-10.6GHz). A peak gain of about 17.4 GHz is observed in the operating band.

Fig 4.2.2 Iteration 2 (Vivaldi antenna with 004 unit cells)

The second iteration of the antenna consists of a metamaterial unit cell at the top and bottom side of the antenna as shown in figure 4.2.2. The peak gain obtained in this case is about 14 dB and the radiation patterns at cutoff frequencies are as shown in figure 4.2.3. Here the antenna frequency band is rejected at 15GHz range.

Fig 4.2.3 Iteration 3 (Vivaldi antenna with 024 unit cells)
A further improvement of adding another row which consists of two metamaterial unit cells has been added to top and flip side of the antenna has been seen in the iteration3.The three iterations of the antenna and proposed model has been designed and simulated using ANSYS Electromagnetic Desktop 17. The unit cell patterns help to improve the performance of the antennas in different frequency bands.
The final design proposed is shown in figure 4.2.4.

Fig 4.2.4 Iteration 4 (Vivaldi antenna with 124 unit cells)

parameter L1 L2 L3 L4 L5 L6 L7 L8 L9
Length in mm 72 42 25.675 1.7 2.13 2.6 58 26 3
Table 4.2.1 Dimensions of antenna

CHAPTER 5
EXPERIMENTAL RESULTS

Fig 5.1 Radiation pattern at 9 Giga hertz for Vivaldi (Iteration 1) antenna

Fig 5.2 Radiation pattern at 17 Giga hertz for Vivaldi (Iteration 1) antenna

Fig 5.3 Polarization pattern at 9 Giga hertz for Vivaldi (Iteration 1) antenna

Fig 5.4 Polarization pattern at 17 Giga hertz for Vivaldi (Iteration 1) antenna

Fig 5.5 Radiation pattern at 9 Giga hertz for 004 (Iteration 2) antenna

Fig 5.6 Radiation pattern at 17 Giga hertz for 004 (Iteration 2) antenna

Fig 5.7 Polarization pattern at 9 Giga hertz for 004 (Iteration 2) antenna

Fig 5.8 Polarization pattern at 17 Giga hertz for 004 (Iteration 2) antenna

Fig 5.9 Radiation pattern at 9 Giga hertz for 024 (Iteration 3) antenna

Fig 5.10 Radiation pattern at 17 Giga hertz for 024 (Iteration 3) antenna

Fig 5.11 Polarization pattern at 9 Giga hertz for 024 (Iteration 3) antenna

Fig 5.12 Radiation pattern at 17 Giga hertz for 024 (Iteration 3) antenna

Fig 5.13 Radiation pattern at 9 Giga hertz for 124 (Iteration 4) antenna

Fig 5.14 Radiation pattern at 17 Ghz for 124 (Iteration 4) antenna

Fig 5.15 Polarization pattern at 9 Giga hertz for 124 (Iteration 4) antenna

Fig 5.16 Radiation pattern at 17Giga hertz for 124 (Iteration 4) antenna

Fig 5.17 E pattern at 9 Giga hertz and 17 Giga hertz for 124 (Iteration 4) antenna

Fig 5.18 J field pattern at 9 Giga hertz for 124 (Iteration 4) antenna

Fig 5.19 J field pattern at 17 Giga hertz for 124 (Iteration 4) antenna

Fig 5.20Comparision of reflection coefficient vs frequency of Iteration 1, 2 and 3

Fig 5.21Comparision of peak gain vs frequency of Iteration 1, 2 and 3

Fig 5.22 Reflection coefficient of Iteration 4

Fig 5.23 Peak gain of Iteration 4

Fig 5.24 Parametric analysis of unit cell length L9
CHAPTER 6
RESULT ANALYSIS

6.1 Results And Discussion:
The reflection coefficient and gain vs frequency of the three iterations has been seen in the fig 5.20 and fig 5.21. Basic Vivaldi antenna i.e., iteration 1 had notch at the higher bands with gain enhancement but by using the metamaterial unit cell the antenna covers good reflection characteristics and standard gain enhancement as shown in the figures. The gain vs frequency plot of the three iterations has been seen in the figure 5.21.
The proposed antenna layout can be viewed in Fig 4.2.4 and its return loss in fig 5.22. In fig 4.2.4 the proposed model which is having 1-2-4 layout of metamaterial unit cells has been seen. The proposed antenna reflection coefficient overs a wide coverage of band up to 24GHz.Illustrated figures 5.22 and 5.23 demonstrate the reflection coefficient and the peak gain obtained respectively. We can tell from the reflection coefficient pattern that the resonant frequencies are obtained at 9GHz and 17 GHz (from the notches obtained). The pattern also ensures that the antenna can be operated in Wide Band as the magnitudes are below -10 dB.
The maximum peak gain of about 14.28 dB is obtained at 20.5 GHz and an average peak gain of 5.7 dB is observed in the operating region. Reflection coefficient as low as -30 dB is observed at frequencies 9GHz and 17 GHz for the antenna proposed in figure 4.2.4.The radiation patterns are shown in the figure at 9 GHz and at 17 GHz. The patterns obtained can be analyzed as directional pattern at 9 GHz and quasi omni-directional at 17 GHz. The E field is represented in red and H field pattern is represented in black.Fig 5.24 shows the parametric analysis of the unit cell length (L9) which analyses the reflection coefficient of antenna with respect to frequency. The unit cell length also plays a major role in the obtained characteristics of antenna.
When L9 is taken as 1.5m we cannot observe any notch in the required frequency band but when L9 is taken as 2mm we can observe notch before 10 GHz but the main aim is to enhance the gain of antenna which is not observed with this measurement. When L9 is taken as 2.5 mm we are not obtaining a sharp notch and a high gain as we obtained in the case when L9 is 3mm. We can observe that all the measurements of L9 provide a good reflection in the required band but a length of 3mm is chosen because it provides the highest gain of about 14.28 dB with a return loss of about -30 dB for the model shown in figure 4.2.4.

6.2 Applications:
• Some of the applications of UWB are there are used in wireless networks and wireless home systems such as computer etc.
• It is used in positioning electronic devices and also mainly it is used in Radar applications.
• Wireless networks such as WPANS and Wi-max are some of the applications of the UWB.
• UWB band requires antennas which are having high gain.
• This antenna can be used in high gain applications.
• They can also serve best in military and civil applications.
• As tapered slots are used,they can be usein covert applications.

CHAPTER 7
CONCLUSION
Vivaldi antenna with metamaterial loaded unit cell which leads to high gain has been designed in this article. The proposed antenna has been illustrated iteration wise. A maximum gain of about 14.5 dB and an average gain of 8.5 dB has been seen throughout the coverage band. A bandwidth of almost 18GHz has been observed in the proposed antenna. The proposed antenna had its applications at high gain devices which are present in the ultra-wide region. The compared results show that the optimized layout can improve obviously the radiation performance especially near the resonance frequency band.

CHAPTER 8
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