Free Space And A Guiding Device Biology Essay

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An antenna is considered as transitional structure between free space and a guiding device. Antenna is a key component in wireless communication systems where it serves as a radiating as well as a receiving device for the signals. In modern world where everything is getting smaller in size, this size reduction and enhanced bandwidth of antenna is the major demand today. To fulfill this demand, microstrip patch antennas are widely used. They have the properties such as light weight, small size and easy manufacturability. Patch antennas have a disadvantage of narrow bandwidth which can be enhanced using several techniques; some of them would be discussed in this report.

1.2 Problem Statement

Ultra wideband technology is used in low power, short range and high bandwidth communication. In UWB information can be transmitted by spreading over a larger bandwidth and also the spectrum is shared with the other users at the same time. Federal Communication Commission (FCC) allocated the band of 3.1GHz-10.6GHz for use in UWB applications. [9] Since then there is an emergent demand of UWB antennas for high data rate applications such as wireless personal area network (WPAN).

1.3 Objective

The objectives of this thesis are to design a microstrip meandered patch UWB antenna and discuss the meandering technique. We will also discuss the return loss and radiation patterns of the designed antenna. Moreover dual behavior of the antenna would be demonstrated in detail.

1.4 Methodology

We have simulated the designed antenna using Ansoft HFSS and CST Microwave Studio both. The simulated results of both simulators are also compared.

1.5 Overview

The report is broken down into 8 chapters. Chapter 1 contains the introduction, background, problem statement, objective and methodology. Chapter 2 contains the fundamental antenna concepts. Chapter 3 is limited to the different types of antennas whereas Chapter 4 has information related to microstrip patch antennas, their different feeding methods and properties of patch antennas. Chapter 5 elaborates the meandered geometry, meandered patch UWB antenna and its various properties. Chapter 6 explains the return loss and radiations patterns of the designed antennas. Chapter 7 is about the fabrication of simulated UWB antenna and Chapter 8 is about conclusion and recommendations.

Chapter 2

2. Antenna Fundamentals

2.1 Radiation Pattern

Radiation pattern is a mathematical function or graphical representation of the radiation properties of an antenna as a function of space coordinates. [1] In most of the cases, radiation pattern is measured in far field. [1] Radiation pattern is represented in 3-D but for the sake of simplicity it can also be represented in 2-D.

Figure-2.1: Radiation Pattern

Radiation properties of an antenna depend on [1]

Power flux density.

Radiation intensity.

Field strength.

Directivity.

Phase or polarization.

The θ and Φ components of electric field and the phases of these fields as a function of θ and Φ completely specify the radiation pattern. [2]

Different parts of radiation pattern are called its lobes and they are classified as

Main or Major Lobe.

Minor Lobe.

Side Lobe.

Back Lobe.

2.1.1 Major Lobe

It is the lobe which contains maximum concentration of radiations.

Minor Lobe

Any other lobe except the major lobe is minor lobe. They represent the radiations in unwanted directions normally.

Side Lobe

A side lobe is adjacent to the main lobe and contains less power as compared to the main lobe.

Back Lobe

The lobe making a 180° angle with the beam of the antenna is known as back lobe.

2.2 Surrounding Fields

Surrounding space around an antenna is termed as field and is classified into [1]

Near field.

Far field.

2.2.1 Near Field

The region just close to the antenna is near field of the antenna. The portion of the near field which immediately surrounds the antenna is called reactive near field while the portion of the near field between the far field and the reactive near field is called radiative near field or Fresnel region. [1]

2.2.2 Far Field

The distance that is larger as compared to the size of the antenna and larger than the wavelength is known as far field region. It is the region where the angular field is independent of the distance from the antenna. [1]

2.3 Directivity and Gain

Directivity of an antenna is the ratio of maximum radiation intensity to average intensity value of the radiations. [2]

D = 4π/ ΩA

ΩA = ΩM + Ωm

Also ΩA = ΦHP. θHP

ΩA is the total beam area and ΦHP, θHP are half power beam widths in two principal planes. Gain is related to the radiation intensity in a particular direction and intensity of radiations by an isotropic antenna. [1]

Gain = (4Ï€ x radiation intensity)/ input power.

An antenna can have maximum gain equal to 1. Gain can be calculated by comparing the maximum power density of antenna under test (AUT) with a reference antenna of known gain.

2.4 Beam width

Beam width is the angle between the direction in which there is maximum intensity of beams and the direction containing half of the maximum intensity of beams. [1] It is also described as angle between two points on the radiation pattern. As the beam width decreases, the side lobes increase. [1] Beam width can be categorized as

Half power beam width (HPBW)

First null beam width (FNBW)

HPBW is the angular beam width at a level when power is half or when E-field level is -3 dB. And the beam width between first nulls is known as FNBW.

Figure-2.2: Half Power & First Null Beam Width

2.5 Bandwidth

Bandwidth is the range of frequencies over which an antenna works efficiently. [1]

For some classes of antenna, bandwidth is taken as ratio of upper to lower frequencies of acceptable operation. [1]

2.6 Polarization

It is orientation of oscillations of electromagnetic waves in space. Polarization is the property of electromagnetic waves which describes the time varying direction and magnitude of the electric field vector.

Polarization phenomenon is categorized into

Linear polarization.

Circular polarization.

Elliptical polarization.

Linear polarization is further classified into

Horizontal polarization.

Vertical polarization.

2.6.1 Linear Polarization

In linear polarization, electric field at point in space as a function of time is directed along a line.

2.6.1.1 Horizontal Polarization

If the polarization direction is along the x-axis, the wave is said to be horizontally polarized. A horizontally polarized wave is expressed as a function of time and E-field position as in [2].

2.6.1.2 Vertical Polarization

When a wave is traveling along y-direction, it is said to be vertically polarized. A vertically polarized wave traveling in positive z direction can be expressed as a function of time and E-field. [2]

Following figure illustrates vertically polarized E-field.

Figure-2.3: Vertically Polarized E-field

2.6.2 Circular Polarization

A wave is circularly polarized if its components have same magnitude but have a phase difference which is odd multiple of π/2. Wave moving in clockwise rotation is said to be left circularly polarized and the one propagating in counterclockwise rotation is right circularly polarized. Circular polarization is mathematically expressed as [2].

E1 is amplitude of wave linearly polarized in x direction.

E2 is amplitude of wave linearly polarized in y direction.

δ is the phase difference by which Ey leads Ex.

Figure-2.4: Circularly Polarized E-field

2.6.3 Elliptical Polarization

A wave is elliptically polarized if its components have unequal magnitude and a phase difference of odd multiple of π/2.

Figure-2.5: Elliptically Polarized E-field

2.7 Beam Efficiency

Beam efficiency of the major lobe is the ratio of beam area of the main lobe to the total beam area of the antenna. [1]

Beam efficiency of minor lobe is the ratio of the beam area of the minor lobe to the beam area of the antenna. It is also known as stray factor. [2]

Chapter 3

3. Antenna Types

3.1 Types of Antennas

Following are the types of antennas

Wire antennas

Aperture antennas

Microstrip Patch antennas

Array antennas

Reflector antennas

Lens antennas

3.1.1 Wire Antennas

Wire antennas are of various forms such as straight wire, loop and helix. These antennas are used in space vehicles, automobiles, ships, on buildings etc. shapes of the wire loop antennas can be square, rectangle, circular, ellipse or any other geometrical shape.

Figure-3.1: Circular loop antenna

3.1.2 Aperture Antennas

These antennas can be easily mounted on the space vehicles and air crafts so they found their wide use in air crafts and space crafts. They can be saved from the harmful effects of the environment by covering them with a layer of some dielectric.

Figure-3.2: Pyramidal horn aperture antenna

3.1.3 Microstrip Patch Antennas

Microstrip patch antennas were developed in 1950's and became popular in 1970's. They are developed on printed circuit technology. They are used for government and commercial applications. In microstrip antennas, a metallic patch is etched on a dielectric substrate. The patch can have different configurations such as rectangular, circular etc. They are famous for their small size, low cost and easy fabrication.

Figure-3.3: Microstrip patch antenna

3.1.4 Array Antennas

Array antennas are used for those applications which need radiation characteristics which cannot be achieved by single radiating component. Array antennas give maximum radiations in one direction and minimum in other directions.

Figure-3.4: Aperture array antenna

3.1.5 Reflector Antennas

These antennas are used in long distance applications where millions of miles are involved. Parabolic reflector and corner reflectors are examples of reflector antennas. These antennas have diameters as large as 305m.

Figure-3.5: Parabolic Reflector Antenna

3.1.6 Lens Antennas

Lens antennas are used to focus energy at the desired points and prevent the energy from spreading in undesired directions. They convert divergent energy to plane waves.

Figure-3.6: Lens Antenna

Chapter 4

4. Microstrip Patch Antennas

4.1 Introduction

Microstrip patch antennas are low profile, small size, and light weight, inexpensive, easy to fabricate, easy to install and have aerodynamic profile. They are mostly used in mobile radio and wireless communication systems. [1]

These antennas inherently have narrow bandwidth, and to enhance their bandwidth is the main demanded for their applications. Size reduction is required for miniaturization of mobile units. [3]

Figure-4.1: Microstrip Antenna

4.2 Properties of Microstrip Antennas

Microstrip antennas are [1]

Small size, light weight and inexpensive.

Low profile and conformable to planar and non-planar surfaces.

Mechanically robust when mounted on rigid surfaces.

Can operate at a band of 100MHz to 100GHz

Versatile in frequency, impedance and polarization patterns.

Can operate at multiple frequency bands.

Ability of rejecting undesired bands by proper designing.

Wideband and ultra wide band operations.

Multiple feeding methods can be used.

4.3 Feeding Methods

Following feeding methods are used with microstrip antennas

Microstrip line feed

Coaxial probe feed

Aperture coupled feed

Proximity coupled feed

These methods are either contacting or non-contacting. [4,5] Contacting methods are those in which there is a direct contact between the transmission line and the radiating surface whereas in non-contacting methods, electromagnetic field coupling method is used to transfer the power. [4]

4.3.1 Microstrip Line Feed

In this feeding method, the line feed is a conducting strip of smaller width. It is easy to fabricate, simple to model. [1] The radiating strip is placed at the edge of the radiating patch. If length of the strip is greater than the wavelength, losses will be generated. A line feed of dimensions 17x3mm is used to obtain 50Ω input resistance.

Figure-4.2: Microstrip Line Feed

4.3.2 Coaxial Probe Feed

As coaxial cable is made up of two conducting wires, in coaxial probe feed one conductor is connected to the radiating surface and the other with ground. In this feeding method, feed can be placed at any point inside the for impedance match. Coaxial probe feed is easy to fabricate and has lower spurious radiations. It is difficult to make and has narrow bandwidth.

Figrue-4.3: Coaxial Probe Feed

4.3.3 Aperture Coupled Feed

Aperture coupled feed consists of two substrates which are separated by a dielectric. The energy is coupled to the patch through a slot on the ground plane through the substrate. There is a feed line on the bottom side of the lower substrate. It is easy to model and has moderate spurious radiations. [6]

Figure-4.4: Aperture Coupled feed

4.3.4 Proximity coupled feed

In proximity coupled feeding method, a microstrip line is placed between two substrates. Radiating patch is placed on the upper substrate. Its capacitive natured coupling is result of open ended line feed. Proximity coupling although difficult to fabricate, has largest bandwidth, easy to model and has low spurious radiations.

Figure-4.5: Proximity Coupled feed

4.4 Disadvantages of Microstrip Antennas

Some of the disadvantages of the microstrip antennas are [1, 4]

They have low gain and efficiency.

Narrow bandwidth.

Poor polarization purity.

Spurious feed radiations.

Poor scan performance.

4.5 Design Procedure

A microstrip antenna consists of a substrate above which a patch is etched using printed circuit technology. Below the substrate there is a ground plate. The patch formed on the top surface, it has several characteristics such as its input impedance varies by varying the width of the patch. A conductive strip is connected to the patch for the feeding purpose. The feed line is thinner in dimension as compared to the patch. The patches can be square, rectangular, square or any other shape. Different substrates can be used for the design of microstrip antennas and their dielectric constant εr varies from 2.2 up till 12. [1]

In case of rectangular patch antenna fringing effects must be taken into account because some waves travel in air and some in the substrate. For this purpose effective dielectric constant εeff is introduced. The following formulae are used to calculate the length L and width W of patch antenna. [1]

Due to the fringing effects the length of the patch increases on either side by a factor ΔL. The formula for calculating effective length is given below. [1]

Leff = L + 2∆L

For this we need the value of ΔL which can be calculated as;

The formula for calculating width W is given below.

For dominant mode TM010 resonant frequency is given as. [1]

4.6 Classification on the basis of bandwidth

Microstrip antennas can be classified on the basis of range of frequency bands on which they operate. Three main classes are

Narrowband antennas

Wideband antennas

Ultra wideband antennas.

Chapter 5

5. Meandered Patch UWB Antenna

5.1 Meandering

The term meander means wandering around or taking an indirect patch. Generally when we talk about meandering a lot of examples come to our minds such as a meander is formed when water moving in a river gradually destroys its banks and widens the entire path. In this way a snake type pattern is created and water takes longer time to pass. This is a natural process which increases the curvature of the path and sinusoidal tracks are created. Following figure demonstrates meanders formed in a river stream.

Figure-5.1: Meanders in river stream

5.2 Meandering in microstrip patch antennas

When we talk about the term "meander" in antenna theory then it has not much difference from the meanders formed in streams. Meandering is done in patch antennas to lengthen the current path so that the current can remain in the patch for a much longer time which causes the antenna to resonate much effectively [3].

Meandering increases the electrical length of the patch as compared to its physical length. This process is done to lower the resonant frequencies and to reduce the antenna size [3]. The resonant frequency is lowered because the current remains for a much longer time in the patch due to the meandering effect.

Meandering is achieved by inserting several narrow slits are at the non-radiating edges if the patch. In this way the current path along the patch is lengthened which results in a lower fundamental resonant frequency [3]. Moreover these slits also introduce a capacitive effect which causes the patch to radiate for a longer time. The position and dimension of the slits determine the resonant frequencies of the patch. Moreover triangular notches can be inserted along the non radiating edges of the patch to form a bow tie geometry which also results in a much lower fundamental resonant frequency. Another important aspect of meandering technique is that it increases the bandwidth.

Figure-5.2: Meandered Patches

5.3 Advantages of using Meandered Geometry

There are several advantages of using meandered geometry in microstrip patch antennas which are; [3]

Lowers the fundamental resonant frequency.

Increases the electrical length of the patch as compared to its physical length.

No hard and fast rule about the slits position.

Increases the bandwidth of the antenna.

It is a simple geometry, no complications involved.

Used in designing small size antennas.

Gain is improved by increasing the width of ground plane and patch.

Impedance bandwidth of the antenna is increased by meandering the ground plane of antenna.

5.4 Previous Work On meandered patch antennas

Some work has been done in past regarding meandered patches. An aperture coupled meandered patch antenna was demonstrated in [7]. The patch was coupled by an H shaped aperture on the ground plane and a high temperature superconductor was used for increasing radiation efficiency. The antenna showed a dual band and multiband behavior. A meandered slot antenna with open ends was also demonstrated in [8]. The purpose of the open ends was to miniaturize the proposed antenna. This antenna also used aperture couple feed and the size was reduced due to the open ends.nna.emonstrated in [B]4848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848 Moreover a planar inverted F antenna (PIFA) with a probe feed was reported in [10]. PIFA is a rectangular patch antenna with meandering technique. It was demonstrated in [10] that bandwidth is increased by inserting slits of suitable dimensions.

All the previous work done on meandered patches either used a probe feed or aperture coupled feed. Moreover the previously designed meandered patches were not for UWB applications. Our aim is to design a UWB antenna using meandered patches with a suitable size and simple geometry.

5.5 Designed Meandered Patch UWB Antenna

As we know that Federal communication system (FCC) allocated frequency band of 3.1GHz to 10.6GHz for use in ultra wideband applications [9]. So a UWB antenna needs to operate within this allocated band. Therefore a meandered patch antenna is designed to operate within this UWB range.

The antenna is fabricated on a dielectric material FR-4 with radiating patch and ground plane made up of copper on the two sides. The dielectric is sandwiched between the ground plane and the patch. FR-4 used has a dielectric constant of 4.7 and height 1.6mm. The length of the patch is 36mm and it has width of 30mm. The length and width of patch were calculated using the formulae mentioned in chapter 4 for rectangular patch using the frequency of 2.45 GHz. Later it was optimized for UWB operation. The antenna is fed using a transmission line of length 16mm and width 2.2mm. Antenna is fed with an asymmetric feed for bandwidth enhancement. The dielectric has a length of 60mm and a width of 70mm. The main hurdle in designing a UWB antenna is bandwidth enhancement. There are several bandwidth enhancement techniques to increase the impedance bandwidth of antenna such as; [11]

Using asymmetrical feed.

Using partial ground plane.

Adjusting the feed gaps.

Inserting a slot in ground plane just beneath the patch.

Using steps to control the impedance.

We have used asymmetrical feed, reduced ground plane and feed gaps technique to enhance the bandwidth of the meandered patch antenna. Good impedance matching is also done by using these methods [11, 12]. All the slits inserted in the non radiating edges have same dimensions with a length of 21mm and width 2mm. the position of slits is adjusted for best return loss. The space between upper edge of reduced ground plane and the lower edge of radiating patch is known as feed gap. A fine adjustment in this gap helps in achieving good impedance matching. The antenna designed has a reduced ground plane with length 14.5mm and width 70mm.

Figure-5.3: Meandered Patch UWB antenna

5.6 Dual behavior of the designed antenna

Primarily this meandered patch antenna was designed with a full ground plane and later on the bandwidth was improved by using the reduced ground plane effect. The bandwidth was also enhanced by controlling the feed gaps. In this way this antenna has a dual behavior due to a reduction in ground plane. It behaves as a multiband antenna with full ground plane whereas UWB operation is achieved by partial ground plane. Figure-5.4(a) (b) shows both the antennas with full and reduced ground plane. The shaded portion in 5.4(b) shows the reduced ground plane where as the white portion in 5.4(a) is the full ground plane. The terms Wp and Lp are the length and width of patch respectively. All other dimensions are the same as mentioned above except the ground plane.

(a) (b)

Figure-5.4: (a) Full Ground and (b) Reduced ground plane antenna

Chapter 6

6. Simulations

The antenna was designed and simulated using both Ansoft HFSS and CST microwave studio. We will discuss the some of the features of HFSS and some from CST.

6.1 Ansoft HFSS

The antenna was first designed and simulated in HFSS (high frequency structure simulator). It is a simulator which gives 3-D design environment. HFSS is an interactive software package for calculating the electromagnetic behavior of a structure. You are expected to draw the structure, specify material characteristics for each object, and identify ports and special surface characteristics. HFSS then generates the necessary field solutions and associated port characteristics and S-parameters. Using HFSS, you can compute:

Basic electromagnetic field quantities and, for open boundary problems, radiated near and far fields.

Characteristic port impedances and propagation constants.

Generalized S-parameters and S-parameters renormalized to specific port impedances.

The Eigen modes, or resonances, of a structure.

Various electromagnetic structures can be designed using this simulator and it has options for different boundary conditions. Ports can be defined using different vector orientations. Moreover polar plots, S11 parameters, 3-D polar plots and many more plots can be viewed using this tool. The most difficult part of using HFSS is defining the port vector which has different effects when defined differently.

6.2 Results

The results of meandered patch UWB antenna are first elaborated then its multiband results are discussed using the same software.

6.2.1 Results of UWB antenna

The return loss of meandered patch UWB antenna is measured first. Antenna is simulated from 1GHz to 16GHz. The antenna designed in HFSS is shown as

Figure-6.1: Meandered Patch UWB antenna in HFSS

The return loss of UWB antenna is obtained at various resonant frequencies. This is the optimized return loss after adjusting the feed gap, reduced ground plane and asymmetric feed. Figure-6-2 shows the return loss of UWB antenna. The point in return loss from 3.8 GHz to 5 GHz shows band rejection characteristics. The return loss shows that the designed antenna works within the UWB range. Moreover the frequency band from 4.4 GHz to 5 GHz is used for military purposes in Europe, so the band rejection characteristic is helpful there. The antenna also satisfies the European UWB range of 6 GHz to 8 GHz.

Figure-6.2: Return loss of UWB antenna

The fractional bandwidth of UWB meandered patch antenna is calculated at different center frequencies and is shown in table.

Resonant Frequency (GHz)

Return loss(dB)

Fractional Bandwidth (%)

3.2

-12.49

31.25

7.5

-21.22

64

12.4

-19.22

13.65

Table 6.1: Resonant frequencies with return loss and fractional bandwidth of UWB antenna.

6.2.2 Results of Multiband antenna

The same antenna works as multiband antenna when designed with a full ground plane instead of using reduced ground plane.

Figure-6.3: Meandered Patch antenna (Multiband)

Figure-6.4: Return loss multiband antenna

There are 6 resonant frequencies in this multiband antenna. The return loss and fractional bandwidth of some of the resonant frequencies is given below in table.

Resonant Frequency (GHz)

Return loss(dB)

Fractional Bandwidth (%)

5.8

-24.84

6.89

9.2

-16.67

4.34

10.5

-14.56

2.86

11.4

-14.57

1.75

Table 6.2: Resonant frequencies with return loss and fractional bandwidth of multiband antenna

6.3 CST Microwave Studio

CST is a very complicated but at the same times a much accurate simulator for electromagnetic structures. It is fast and memory efficient. It has following characteristics.

Extremely good performance due to Perfect Boundary Approximation for solvers using hexahedral grids.

The structure can be viewed either as a 3D model or as a schematic. The latter allows for easy coupling of the EM simulation with circuit simulation.

Feature based hybrid modeler allows quick structural changes  

Transient solver for efficient calculation for loss-free and lossy structures. The solver does a broadband calculation of S-parameters from one single calculation.

Frequency domain solver with adaptive sampling.

Besides the general purpose solver, the frequency domain solver also contains two solvers being specialized on strongly resonant structures (hexahedral meshes only). The first of these solvers does only calculate S-parameters whereas the second one also calculates fields which requires some additional calculation time.

Calculation of 3D Eigen modes.

Expert system based automatic mesh generation with 3D adaptive mesh refinement.

Import and Export of SAT, Step, Autodesk Inventor, VDA-FS CATIA, Pro/E, IGES or STL 3D CAD data.

Import and Export of DXF 2D CAD data.

Import GDSII and Gerber 2D CAD data.

Far field (2D, 3D, gain, angular beam width and more) and radar cross section (RCS) calculation.

6.3.1 Results of UWB antenna

Same UWB antenna is designed in CST using same dimensions to verify the results of HFSS. The return loss f UWB antenna is calculated in CST and the results of both simulators are compared.

Figure-6.5: Meandered Patch UWB antenna in CST

Figure-6.6: A comparison of return loss from CST and HFSS (UWB antenna)

The dashed line return loss is the one from HFSS and the solid line is the CST return loss. Both the simulators show almost the same result. CST simulated antenna also satisfies the UWB frequency range criteria. There is a band rejection characteristic in the solid line return loss but it ranges from 4.2 GHz to 4.7 GHz.

6.3.2 Results of Multiband antenna

Similarly the multiband antenna is also designed and simulated in CST and the return loss is compared which almost the same as was the case in UWB antenna. The dashed line graph is the one from HFSS and the solid line graph is from CST microwave studio. Both the return loss graphs are almost the same which verifies our results.

Figure-6.7: A comparison of return loss from CST and HFSS (Multiband antenna)

6.4 Radiation Pattern

We would be discussing the radiations pattern of meandered patch UWB antenna in detail as shown.

6.4.1 Radiation pattern at 2.4 GHz

The plots show the theta and phi plot radiation patterns of the UWB meandered patch antenna. There is more rotation in theta plane as compared to phi plane. So it is co- polarized at 2.4 GHz. Gain is also very good in phi plot which is 4.8 dBi. The radiation pattern also shows the hag power beam width.

(a)

(b)

Figure-6.8: Radiation patterns at 2.4 GHz. (a) Theta plot (b) Phi plot

6.4.2 Radiation pattern at 5.2 GHz

The phi plot shows the directional pattern with a peak main lobe magnitude of 7 dBi. The antenna shows a very good gain with phi plot showing more cross polarization characteristics.

(a)

(b)

Figure-6.9: Radiation patterns at 5.2 GHz (a) Theta plot (b) Phi plot

6.4.3 Radiation pattern at 8 GHz

The phi plot shows an omnidirectional pattern at the center frequency. But the gain is not very good at 8GHz. Phi plot shows more variation in phi plane rather than theta plane so the antenna shows cross-polarization at 8GHz.

(a)

(b)

Figure-6.10: Radiation patterns at 8 GHz (a) Theta plot (b) Phi plot

6.4.4 Radiation pattern at 13 GHz

The phi plot shows a peak gain of 5.7 dBi. The radiation pattern shows better co-polarization.

(a)

(b)

Figure-6.11: Radiation patterns at 13 GHz (a) Theta plot (b) Phi plot

6.5 Gain of Meandered Patch UWB antenna

The gain vs. frequency plot is shown in figure. It shows that the UWB antenna has a gain that is much better and this is due to the wider patch and ground plane.

Figure-6.12: Gain vs. Frequency plot for UWB antenna

6.6 Gain of Meandered Patch Multiband antenna

Gain vs. frequency plot for meandered patch multiband antenna is shown in figure and this antenna also has a good gain at various frequencies.

Figure-6.13: Gain vs. Frequency plot for Multiband antenna

Chapter 7

7. Fabrication of Simulated UWB Antenna

7.1 Introduction

We fabricated the meandered patch UWB antenna ourselves. There were few steps involved in the fabrication of this antenna. Care should be taken during the fabrication because it is a very delicate process. Any slight human error may cause the results to vary abruptly. The dielectric used should be double sided copper coated with dielectric sandwiched between the copper. The fabrication steps are discussed below.

7.2 Cutting the Dielectric Sheet

The first and foremost step of fabrication is cutting the required dimensions of dielectric from the dielectric sheet. We marked the dimensions on the dielectric sheet and cut it to take out our desired element.

7.3 Marking the Required area on the Dielectric

After cutting the desired element from the sheet

We have to mark the patch area on the front side and ground plane area on the back side of dielectric.

After marking the required area we covered it so that the next step is carried out perfectly.

The marking process can be done by;

Taking the prints of patch and ground plane on butter paper sheet, then ironing the butter paper on the substrate that was cut earlier. This will deposit the image of patch that was printed in black ink. So the patch area will be covered up by ink and later it will not react with Ferric Chloride (FeCl3). Similarly we can cover the patch area for the reduced ground plane.

Another way is to make the boundaries of the patch by taking a print on the paper and taking out the patch, ground plane area by cutting it with paper cutter. After that place the printed patch on the substrate sheet and make the patch area with lead pencil. Then cover the marked area with a permanent marker. In this way the copper will be covered up and it will not react with FeCl3.

We used the latter process by covering the patch and ground plane area with permanent marker.

7.4 Reaction with Ferric Chloride Powder

After covering the required area follow these steps.

Take some hot water in a deep bowl; it should be enough to immerse the sliced dielectric.

Add 3-4 table spoons of ferric chloride powder into hot water. It will mix up with water quickly.

The spoon and bowl should not be made up of any metal otherwise the ferric chloride solution will react with them.

Immerse the sliced dielectric into the solution and stir it for some time. The reaction will start and FeCl3 solution will react with copper on both sides of the substrate.

The copper will be removed from the substrate due to reaction with the FeCl3 solution. Now take out the fabricated substrate and wash it with water.

Copper will retain its position only on the covered area.

Now you can remove the permanent marker ink by cleaning it with perfume or body spray or petrol.

The next step is to solder the connector.

7.5 Soldering the SMA Connector

The final step of fabrication is soldering the SMA 50-Ω connector. Solder the pin of the connector with the transmission line and the back side with the ground plane. Now the antenna is fabricated and ready to be tested. Figure 7.1 and 7.2 show the fabricated meandered patch UWB antenna.

Figure-7.1: Fabricated UWB antenna (Top side)

Figure-7.2: Fabricated UWB antenna (Back side)

Chapter 8

8. Conclusion and Future Recommendations

8.1 Conclusion

In this thesis antenna for UWB applications has been presented. The antenna has a minimum return loss of -10dB over the UWB range set by FCC. It has been shown that by properly selecting the slits dimension multiband behavior with bandwidth enhancement can be achieved. The UWB characteristics can be achieved by understanding of partial ground and feed gap. These techniques help in obtaining high impedance matching and improved impedance bandwidth. The line feed used to excite the patch makes fabrication process easier. Small size of the antenna makes it suitable for applications which demand miniaturization of the antenna structure.

8.2 Future Work

The antenna mentioned in this thesis can be further modified and improved by using several techniques such as.

The UWB antenna operates in the frequency range of 3.1-10.6 GHz. The WLAN IEEE 802.11 operates at 5.1-5.825 GHz. Moreover some other networks also operate near 3.5 GHz such as fixed broad wideband access. This can cause interference in the UWB range. So to overcome this issue, a band reject filter can be designed that rejects the frequency range which causes interference. Several band notched filters have been demonstrated earlier in [13-16] using techniques such as parasitic patches, slot ring resonators, inserting inverted L and C shaped slits in the patch. One of these methods can be applied to design a band reject filter in the proposed antenna.

Another modification can be made in this design by using the antenna diversity to overcome the fading effect. It is achieved by integrating multiple antennas in mobile terminals and then combining the received signal. This results in high data rate transmissions over wireless communication systems [17, 18].

Appendix A

How to Use CST Microwave Studio

When CST design Environment is opened, select CST microwave Studio option for creating a new project as shown;

After that select the template "Antenna (on planar substrate)" for designing microstrip patch antenna.

After that click the drop down menu "edit" and adjust your working plane properties accordingly as shown;

Size = 100

Width = 2 Auto checked

Snap width = 0.01 Snap checked

*You can adjust these properties according to your own requirements as well.

1. Drawing the Substrate

Go to the objects drop down menu and select Brick from basic shapes option or simply click brick from the basic shapes given in the main window as shown.

Then a window will open to enter the starting point of your substrate.

After entering the starting point, enter the ending point and the height by pressing the tab key. Onwards the brick properties will open with all the dimensions as shown.

Selecting the material for substrate

In the properties window of the substrate, click the drop down menu of material and click on "New material".

You can rename the material name, and change the parameters as shown in figure.

2. Drawing the Patch and Transmission line

Draw the patch and transmission line by drawing the bricks in the similar manner as done above. But Select the material PEC for the patch and transmission line with thickness 0.035.

Afterwards select the patch from components and press ctrl key and click on transmission line. Then used the Boolean Add option to join the patch with transmission line as shown.

3. Defining a wave port

The following calculation of S-parameters requires the definition of ports through which energy enters and leaves the structure. You can do this by simply selecting the corresponding faces before entering the ports dialog box.

For the definition of the first port, perform the following steps:

Set the structure in a position from where you can select the transmission line face and define wave port for excitation.

Select ObjectPickPick Face () from the main menu.

After selecting the face, click on the wave guide port option and give the dimensions of the port as follows.

Width of port = 4.5 x width of transmission line

Length of port = 4.5 x height of substrate

The window for defining port dimension is shown below.

4. Defining Frequency Range

Define the frequency range for the designed antenna by clicking the drop down tab Solve and then choosing the frequency option.

5. Selecting boundary conditions

Choose the appropriate boundary conditions for the designed antenna as it would we influenced by outer atmosphere. Therefore selecting proper boundary conditions is necessary.

Select the Boundary Conditions menu from the solve drop down tab.

You can also define far field monitors by selecting it from the Solve tab.

6. Start the Simulation

After defining all necessary parameters, you are ready to start your first simulation. Start the simulation from the transient solver control dialog box: SolveTransient Solver. As shown.

Apply these settings and start the transient solver. CST will automatically generate all the results required.

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