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Compact Ring Slot Antenna With Multiband Applications

CHAPTER 1

INTRODUCTION

1.1 Introduction

In recent years, the demand for antennas with multiband

operations has been increased rapidly since such antennas play a major role in

combining multiple communications standards in a single compact wireless

system. An antenna is a device that is used to convert guided electromagnetic

waves into electrical signals and vice versa (i.e. either in transmitting mode or in

receiving mode of operation). Antennas are frequency dependent devices. Each

antenna is designed for a certain frequency band and outside of this band, antenna

rejects the signal. Therefore we can say antenna is a band pass filter and

transducer. Antennas are essential part in communication systems therefore

understanding their basics are important. With the advances in tele-

communication, the requirement for compact antenna has increased significantly.

In mobile communication, the requirement for smaller antennas is quite large, so

significant developments are carried out to design compact, minimal weight, low

profile antennas for both academic and industrial communities of

telecommunication. The technologist focused into the design of microstrip patch

antennas. Many varieties in designing are possible with microstrip antenna. A slot

antenna consists of a metal surface, usually a flat plate, with one or more holes or

slots cut out. When the plate is driven as an antenna by a driving frequency, the

slot radiates electromagnetic waves in a way similar to a dipole antenna. The

shape and size of the slot, as well as the driving frequency, determine the radiation

pattern. Slot antennas are used typically at frequencies between 300 MHz and 24

GHz. The slot antenna is popular because they can be cut out of whatever surface

they are to be mounted on, and have radiation patterns that are roughly Omni

directional (similar to a linear wire antenna). The polarization of the slot antenna

is linear. The slot size, shape and what is behind it (the cavity) offer design

variables that can be used to tune performance. The first chapter provides an

introduction to microstrip patch antennas with their advantages and disadvantages.

Then the feeding techniques, analysis method and different parameters of

Department of Electronics and Communication Engineering


microstrip patch antenna are presented.

1.2 Literature Survey

Antennas integrated with both functions of receiving

antenna and low-pass filter simultaneously, can help to eliminate the insertion loss

of filter itself in the microwave power transmission (MPT) systems and then

improve the rectification efficiency [1]. It can also be used in active antenna

systems to effectively suppress harmonic radiation caused by active devices [2].

For microstrip patch antennas with unidirectional radiation characteristics, some

configurations with harmonic suppression have been proposed, such as by cutting

slits in patch elements, or by introducing band-rejected cells in feed structures in

combination with the choice of feed point [3], [4]. For printed slot antennas with

bidirectional radiation, the harmonic suppression can also be implemented based

on the band-notched units in the feed structure. In [2] the DGS structure is placed

at the coupling position between the microstrip feedline and the slot element to

achieve broadband harmonic rejection. Similarly, in [5] a 1/4 wavelength

conductor stub is added in the coupling slot, and in order to achieve the compact

feature the rectangular slot element is further subjected to the bending process.

The introduction of the band-stop structure at the feed side of the antenna is

essentially the same as using the filter, except that it is closer to the antenna

element [6]. To achieve harmonic suppression by adjusting the shape of the slot

element, in [7] the rectangular slot is transformed into a sawtooth shape with the

Bragg reflection. In [8], the harmonic suppression is realized by using both the T-

shaped terminal of the microstrip feedline and the U-shaped conductor in the

coupling slot. The radiating element circumference of the ring slot antenna is

approximately one wavelength of the fundamental resonant mode, and the

harmonic suppression is usually implemented by loading the band-rejected unit in

the feedline or the corresponding ground plane [2], [6]. In this case, the antenna

size is relatively large. For the rectangular slot antenna, the method bending the

narrow slot is applied to achieve miniaturization [5], [9]. However, there are few

reports to miniaturize ring slot antennas at present [10]. In this project, it is

proposed that the square ring slot is miniaturized by the loading of two side slots,

and a slot resonator is introduced at the feed side to realize the multiband



applications.

1.3 Motivation of the Project

In order to overcome the difficulties from the literature

survey, there is an immense need for a compact ring slot antenna which can

exhibit multiband characteristics in order to facilitate the wireless applications.

1.4 Aim of the Project

The aim of the project is to design a compact ring slot

antenna which exhibit multiband characteristics covering four bands of wireless

communication. The design validated by using a simulating software Ansys-

HFSS.

1.5 Organization of the Thesis

This thesis is divided into 6 chapters and organized as

follows:

Chapter 2 deals with the brief description of the proposed antenna and its

parameters.

Chapter 3 proposes the geometry of Compact ring slot antenna with multiband

applications and its theoretical analysis.

Chapter 4 deals with the design analysis of project.

Chapter 5 deals with the fabrication and results obtained.

Chapter 6 ends with the conclusion and future scope.



CHAPTER 2

OVERVIEW

2.1 Introduction

This Chapter aims to give the brief description of the

proposed antenna and its parameters.

2.2 Introduction to Antennas

An antenna is used to radiate electromagnetic energy

efficiently and in desired directions. An antenna act as matching systems between

sources of electromagnetic energy and space. The goal in using antennas is to

optimize this matching.

The properties of antenna are as follows:

Field intensity for various directions (antenna pattern).

Total power radiated when antenna is excited by a current or voltage of

known intensity.

Radiation efficiency which is the ratio of power radiated to the total

power.

The input impedance of antenna for maximum power transfer.

The bandwidth of the antenna or range of frequencies over which the

above properties are nearly constant.

2.3 Microstrip Patch Antenna

Nowadays, in mobile communication systems, the requirement of small sized

antenna for miniaturization purpose of mobile units has been increased. Hence,

reduced size and enhanced bandwidth are the major considerations in micro strip



antennas for practical applications. Therefore, Study regarding small size and

enhanced bandwidth of micro strip antenna has been greatly increased. In the past

few years, great progress in the design of small sized micro strip antenna with

Dual and circular polarization, dual frequency, broadband and gain enhanced

performance has been reported.

Fig 2.1 Patch Antenna

Howell and Munson developed the first antenna which was practical antenna.

Munson showed that the micro strip antenna was a practical antenna to be used in

various antenna system problems by using it in missiles and rockets as a flush

mounted low-profile antenna. Micro strip antenna consists of a conducting patch

on upper side of dielectric substrate and a ground plane on the lower side of

Dielectric substrate. The material of patch is copper or gold and the patch can

have any shape such as rectangular and circular etc. On the dielectric substrate the

feed line and the patch are photo Etched.

Wireless technology provides less expensive alternative and a flexible way for

communication. Antenna is one of the important elements of the wireless

communications systems. According to the IEEE Standard Definitions, the

antenna or aerial is defined as “a means of radiating or receiving radio waves". In

other words, antennas act as an interface for electromagnetic energy, propagating

between free space and guided medium.

Microstrip patch antennas are widely used in the microwave frequency region

because of their simplicity and compatibility with printed-circuit technology,

making them easy to manufacture either as stand-alone elements or as elements of

arrays. The advantages of micro strip antennas make them suitable for various

applications like, vehicle-based satellite link antennas, global positioning systems



(GPS), radar for missiles and telemetry and mobile handheld radios or

communication devices. In its simplest form a micro strip patch antenna consists

of a patch of metal, generally rectangular or circular (though other shapes are

sometimes used) on top of a grounded substrate.

The commonly available shapes of patch antenna are rectangular, circular, dipole,

triangular, square and elliptical with rectangular and circular shapes the most

common planar transmission lines are lines with conductors, or in some

cases dielectric strips, that are flat, ribbon-shaped lines. They are used to

interconnect components on printed circuits and integrated circuits working

at microwave frequencies because the planar format fits in well with the

manufacturing methods for these components. Transmission lines are more than

simple interconnections. With normal interconnections the propagation of

the electromagnetic wave along the wire is fast enough to be considered

instantaneous, and the voltage at each end of the wire can be considered identical.

2.3.1 Advantages of Microstrip Antenna

Microstrip antenna has several advantages compared to

conventional microwave antennas. These antennas are used in many applications

over the broad frequency range from 100MHz to 50GHz.

Low weight, low cost, low profile and conformal

Easy to fabricate and can be integrated with other microstrip

components in monolithic application like RFIC and MMIC.

The antenna can be easily mounted on missiles, rockets and satellite

without major alterations.

The antenna has low scattering cross section.

Dual frequency antenna can be easily made.

Microstrip antennas are compatible with modular designs (Solid state

devices such as oscillators, amplifiers, variable attenuators, mixer,

phase shifters etc., can be added directly to the antenna substrate

board).



2.3.2 Disadvantages

Narrow bandwidth.

Radiation efficiency deteriorates as frequency and antenna array

size increases due to an increase in the feeding network losses.

Lower power handling capacity.

Poor isolation between the feed and the radiating elements.

2.3.3 Applications of Patch Antenna

Satellite communication

Mobile communication

Missile telemetry

Biomedical radiator

Radar system

Radio altimeter

2.3.4 Microstrip Antenna Parameters

In the microstrip antenna the upper surface of the dielectric

substrate supports the printed conducting strip which is suitably contoured while

the lower surface of the substrate is backed by a conducting ground plane . Such

antenna sometimes called a printed antenna because the fabrication procedure is

similar to that of a printed circuit board. Many types of microstrip antennas have

been evolved which are variations of the basic structure. Microstrip antennas can

be designed as very thin planar printed antennas and they are very useful elements

for communication applications.

Fig 2.2 Basic Structure of Microstrip Patch Antenna

So many advantages and applications can be mentioned for microstrip patch

antennas over conventional antennas. There are several undesirable features we



encountered with conventional antennas like they are bulky, conformability

problems and difficult to perform multiband operations so on. The advantages

include planar surface, possible integration with circuit elements, small surface,

generate with printed circuit technology and can be designed for dual and

multiband frequencies. Disadvantages include narrow bandwidth, low RF power

handling capability, larger ohmic losses and low efficiency because of surface

waves etc. For the last two decades, researchers have been struggling to overcome

these problems and they succeeded many times with their novel designs and new

findings.

2.4 Feed Methods

There are mainly four basic methods for the feeding to

these antennas Probe Coupling Method Microstrip Line Feeding Method Aperture

Coupled Microstrip Feed Method Proximity Coupling Method

2.4.1 Probe Coupling Method

Coupling of power to the microstrip patch antenna can be

done by probe feeding method. The inner conductor of the probe line is connected

to patch lower surface through slot in the ground plane and substrate material . To

get perfect impedance matching we need to find out the location of the feed point

over the antenna element.



Fig 2.3 Probe Coupling Method (a) Top view (b) Side view

Design simplicity and input impedance adjustment through feed point positioning,

makes this feeding method popular. But there are some limitations also like larger

lead for thicker substrate, difficulty in soldering for array elements etc.

2.4.2 Microstrip Line feeding Method

Using microstrip line we can give excitation to the antenna as shown in the fig. This method is very simple to design and fabricate. But this technique suffers from some limitations. If substrate thickness is increased in the design then the surface waves and the spurious radiation also increases. Because of that the undesired cross polarization radiation arises. Microstrip line feeding can be used in the conditions where performance of the antenna is not a strict matter. The edge coupled feed can be improved with coplanar wave guide feeding.

Fig 2.4 Geometry Of Direct Microstrip And Feed Microstrip –Patch

Antenna (a) Top view (b) Side view



Fig 2.5 Geometry of Recessed Microstrip Line Feed Patch Antenna

(a) Top view (b) Side view

2.4.3 Proximity Coupled Method

This method can be employed, where two or multilayer

substrate configuration is considered. Generally in this configuration, microstrip

line will be placed on lower substrate and the patch element will be placed on the

upper substrate. Other name for this feeding is electromagnetically coupled feed.

Capacitive nature will appear between feed line and patch in this case. By

choosing thin lower substrate layer and placing patch on top layer will improve

the bandwidth and reduce the spurious radiation. Fabrication of this feeding is

slightly difficult because of alignment problems in feed and patch at proper

location. Peaceful thing is soldering and related problems can be eliminated.

Fig2.6 Geometry of Proximity Coupled Microstrip Feed Patch Antenna




Fig2.7 Geometry Of Patch Antenna Fed By An Adjacent Microstrip Line


2.4.4 Aperture Coupled Feed Method

This method employs ground plane between two substrates. A slot will be placed

on the ground plane and feed line will be placed on lower substrate. This will be

electromagnetically connected to patch on the upper substrate through the ground

plane slot. One should take care about substrate parameters

and they have to choose in a way that feed optimization and independent radiation

functioning can exist. The coupling slot should be nearly cantered so that the

patch magnetic field will be maximum. Coupling amplitude can be calculated by



Fig 2.8 Geometry of Aperture Coupled Feed Microstrip Patch Antenna

(a) Top view (b) Side view (c)Pictorial view

2.5 Substrate-FR4

FR-4 (or FR4) is a NEMA grade designation for glass-

reinforced epoxy laminate material. FR-4 is a composite material composed of

woven fiberglass cloth with an resin binder that is flame resistant (self-

extinguishing)."FR" stands for flame retardant, and denotes that the material

complies with the standard UL94V-0.

The designation FR-4 was created by NEMA in 1968.FR-4 glass epoxy is a

popular and versatile high-pressure thermo set plastic laminate grade with good

strength to weight ratios. With near zero water absorption, FR-4 is most

commonly used as an electrical insulator possessing considerable mechanical

strength. The material is known to retain its high mechanical values and electrical

insulating qualities in both dry and humid conditions. These attributes, along with

good fabrication characteristics, lend utility to this grade for a wide variety of

electrical and mechanical applications. Grade designations for glass epoxy

laminates are: G10, G11, FR4, FR5 and FR6. Of these, FR4 is the grade most

widely in use today. G-10, the predecessor to FR-4, lacks FR-4's self-

extinguishing flammability characteristics.

Hence, FR-4 has since replaced G-10 in most applications.FR-4 epoxy resin

systems typically employ bromine, a halogen, to facilitate flame-resistant

properties in FR-4 glass epoxy laminates. Some applications where thermal

destruction of the material is a desirable trait will still use G-10 non flame

resistant.

FR-4 is a common material for printed circuit boards (PCBs). A thin layer of

copper foil is laminated to one or both sides of an FR-4 glass epoxy panel. These

are commonly referred to as copper clad laminates. When ordering a copper clad

laminate board, the FR-4 and copper thickness can both vary and so are specified

separately. In the USA, copper foil thickness is specified in units of ounces per

square foot (oz/ft2), commonly referred to simply as ounce. Common thicknesses



are 1 oz/ft2 (300 g/m2), 2 oz/ft2 (600 g/m2), and 3 oz/ft2 (900 g/m2).

These work out to thicknesses of 34.1 µm (1.34 thou), 68.2 µm (2.68 thou), and

102.3 µm (4.02 thou), respectively. Some PCB manufacturers refer to

1 oz/ft2 copper foil as having a thickness of 35 µm (may also be referred to as

35 μ, 35 micron, or 35 mic).

1/0 - denotes 1 oz/ft2 copper one side, with no copper on the other side.

1/1 - denotes 1 oz/ft2 copper on both sides.

H/0 or H/H - denotes 0.5 oz/ft2 copper on one or both sides, respectively.

2/0 or 2/2 - denotes 2 oz/ft2 copper on one or both sides, respectively.

2.5.1 PROPERTIES

FR-4 does not specify specific material, but instead a grade

of material, as defined by NEMA LI 1-1998 specification. Typical physical and

electrical properties of FR-4 are as follows. The abbreviations LW (lengthwise,

warp yarn direction) and CW (crosswise, fill yarn direction) refer to the

conventional perpendicular fiber orientations in the XY plane of the board (in-

plane). In terms of Cartesian coordinates, lengthwise is along the x-axis, crosswise

is along the y-axis, and the z-axis is referred to as the through-plane direction.

Keep in mind that the values for the parameters listed below are an example for a

certain manufacturer's material. Each manufacturer will have slightly different

values for the parameters listed below. It's better to check the datasheet of the

specific material being used. Verifying the actual values is very important for high

frequency designs.

Table 2.1 FR4_epoxy actual values



Table 2.2 FR4_epoxy Specifications



2.6 Block Diagram of the Proposed Antenna

The block diagram of compact ring slot antenna with

multiband applications is shown in fig.2.

Fig.2.10 Block Diagram of the Proposed Antenna

For conventional square or annular ring slot antennas fed using microstrip or

coplanar waveguide (CWP), the ring slot can be equivalent to the parallel

connection of two half-wavelength slot dipole antennas and therefore has better

directionality. However, due to the influence of the feed structure, the second

harmonic of the ring slot antenna easily exhibits the dual resonance characteristic.

At the third harmonic, it completely turned into the large bandwidth with weak

resonant radiation [11]. Therefore, when the ring slot antenna is applied to MPT

or active antenna systems, it is more important to suppress the second-order

harmonic. Since the equivalent LC resonators in the feed position can achieve

band-stop characteristics, a narrow slot resonator orthogonal to the feed line is

introduced outside the square ring slot. In this way, the operating band and the

harmonic suppression can be independently adjusted to a certain extent by the



radiating slot element and the band-notched slot unit. This antenna structure is

shown in Fig. 1(a), and referred to as Ant A. At this point the fundamental mode

frequency is completely determined by the slot ring circumference, and the

antenna size is relatively large. If two side slots are symmetrically loaded at both

ends of a narrow transverse slot to form an H-shaped slot antenna, the uniformity

of electric field distribution in the original transverse slot can be increased and the

transverse slot length is shortened [12]. This structure also contributes to the

weakening of high-order mode radiation due to the increase of the antiphase field

components [13]. Inspired by the H-shaped slot antenna and starting from the

reference antenna Ant A, two parallel slits are loaded symmetrically on both sides

of the square ring slot to realize the compact slot antenna with harmonic

suppression. This proposed slot antenna is called Ant B and its structure is shown

in Fig. 1(b). Its structural parameters are shown in Fig. 1(c) which is also used to

characterize Ant A's structural variables. Since the upper and lower halves of the

slot ring are connected in series with the side slots after being connected in

parallel, in order to meet the impedance matching the characteristic impedance of

the side slots should be reduced [12]. Therefore, the width of the side slots should

be larger than that of the ring slot.

2.7 Conclusions

The importance and role of antenna and the introduction to

the project along with block diagram has been explained in this chapter. The

theoretical analysis of the proposed antenna is described in the next chapter.



CHAPTER 3

THEORETICAL ANALYSIS

3.1 Introduction

This Chapter aims to give the brief description of

theoretical analysis of the proposed antenna.

3.2 Geometrical Configuration

For conventional square or annular ring slot antennas fed

using microstrip or coplanar waveguide (CWP), the ring slot can be equivalent to

the parallel connection of two half-wavelength slot dipole antennas and therefore

has better directionality. However, due to the influence of the feed structure, the

second harmonic of the ring slot antenna easily exhibits the dual resonance

characteristic. At the third harmonic, it completely turned into the large bandwidth

with weak resonant radiation. Therefore, when the ring slot antenna is applied to

MPT or active antenna systems, it is more important to suppress the second-order

harmonic. Since the equivalent LC resonators in the feed position can achieve

band-stop characteristics, a narrow slot resonator orthogonal to the feed line is

introduced outside the square ring slot. In this way, the operating band and the

harmonic suppression can be independently adjusted to a certain extent by the

radiating slot element and the band-notched slot unit. This antenna structure is

shown in Fig. 1(a), and referred to as Ant A. At this point the fundamental mode

frequency is completely determined by the slot ring circumference, and the

antenna size is relatively large. If two side slots are symmetrically loaded at both

ends of a narrow transverse slot to form an H-shaped slot antenna, the uniformity

of electric field distribution in the original transverse slot can be increased and the

transverse slot length is shortened.

Table 3.1 Dimensions of the reference and proposed antennas



Fig.3.1 (a) Front view photograph of the reference antenna Ant A,(b) front view photograph of the proposed antenna Ant B, and (c) schematic

illustration of the antenna structure parameters.

This structure also contributes to the weakening of high-order mode radiation due

to the increase of the anti-phase field components. Inspired by the H-shaped slot

antenna and starting from the reference antenna Ant A, two parallel slits are

loaded symmetrically on both sides of the square ring slot to realize the compact

slot antenna with harmonic suppression. This proposed slot antenna is called Ant

B and its structure is shown in Fig. 1(b). Its structural parameters are shown in

Fig. 1(c) which is also used to characterize Ant A's structural variables. Since the

upper and lower halves of the slot ring are connected in series with the side slots

after being connected in parallel, in order to meet the impedance matching the

characteristic impedance of the side slots should be reduced. Therefore, the width

of the side slots should be larger than that of the ring slot.

3.3 Conclusion

To design the antenna we have considered all the parameters mentioned in

this chapter for better performance of it.



CHAPTER 4

DESIGN METHODOLOGY

4.1 Introduction to HFSS

The name HFSS stands for High Frequency Structural

Simulator. HFSS is a high-performance full-wave electromagnetic (EM) field

simulator for arbitrary 3D volumetric passive device modeling that takes

advantage of the familiar Microsoft Windows graphical user interface. It

integrates simulation, visualization, solid modeling, and automation in an easy-to-

learn environment where solutions to 3D EM problems are quickly and accurately

obtained. Ansoft HFSS employs the Finite Element Method (FEM), adaptive

meshing, and brilliant graphics to give unparalleled performance and insight to all

of 3D EM problems. HFSS is an interactive simulation system whose basic mesh

element is a tetrahedron. This allows to solve any arbitrary 3D geometry,

especially those with complex curves and shapes, in a fraction of the time it would

take using other techniques. Ansoft pioneered the use of the Finite Element

Method (FEM) for EM simulation by developing/implementing technologies such

as tangential vector finite elements, adaptive meshing, and Adaptive Lanczos-

Pade Sweep.

The Ansoft HFSS Desktop provides an intuitive, easy-to-use interface for

developing passive RF device models. Creating designs, involves the following:

1. Parametric Model Generation – creating the geometry, Parametric Model

Generation boundaries and excitations

2. Analysis Setup – defining solution setup and frequency sweep Analysis Setup

3. Results – creating 2D reports and field plots Results



4. Solve Loop - the solution process is fully automated Solve Loop.

4.1.1 Application of HFSS

Today, HFSS continues to lead the industry with innovations such as

Modes-to-Nodes and Full-Wave Spice. Ansoft HFSS has evolved over a period of

years with input from many users and industries. In industry, Ansoft HFSS is the

tool of choice for high-productivity research, development, and virtual

prototyping. HFSS finds applications in wide range of areas. Ansoft HFSS can be

used to calculate parameters such as S-Parameters, Resonant Frequency, and

Fields.

Some of applications of HFSS are:

1. Package Modeling–BGA, QFP, Flip-Chip

2. PCB Board Modeling–Power/Ground planes, Mesh Grid Grounds, Backplanes

Silicon/GaAs-Spiral Inductors, Transformers

3. EMC/EMI –Shield Enclosures, Coupling, Near-or Far-Field Radiation

4. Antennas/Mobile Communications–Patches, Dipoles, Horns, Conformal Cell

Phone Antennas, Quadrafilar Helix, Specific Absorption Rate(SAR), Infinite

Arrays, Radar Cross Section(RCS),Frequency Selective Surfaces(FSS)

5. Connectors–Coax, SFP/XFP, Backplane, Transitions

6. Waveguide–Filters, Resonators, Transitions, Couplers

7. Filters–Cavity Filters, Microstrip, Dielectric.

8. Microwave transitions

9. Waveguide components

10. Three-dimensional discontinuities

11. Passive circuit elements

4.1.2 HFSS Features

HFSS has many significant features which attracts the user. Some of the features

of HFSS are:

1. Computes s-parameters and full-wave fields for arbitrarily-shaped 3D passive structures.



2. Powerful drawing capabilities to simplify design entry.

3. Field solving engine with accuracy-driven adaptive solutions.

4. Powerful post-processor for unprecedented insight into electrical performance.

5. Advanced materials.

6. Model Library-including spiral inductors.

7. Model half, quarter, or octet symmetry.

8. Calculate far-field patterns.

9. Wideband fast frequency sweep .

10. Create parameterized cross section models- 2D models .

4.2 Design Procedure for Edge Feed U Slot Circular Microstrip Patch

Antenna

STEP: 1 Launching Ansoft HFSS

To access Ansoft HFSS, click the Microsoft Start button, select Programs

and select the Ansoft > HFSS program group. Click HFSS.

Fig.4.1 The HFSS Environment



STEP: 2 Setting Tool Options

To set the tool options:

1. Select the menu item Tools > Options > HFSS Option

2. HFSS Options Window

i) Click the General General tab

Use Wizards for data input when creating new boundaries:

Checked

Duplicate boundaries with geometry: Checked

ii) Click the OK button

3. Select the menu item Tools > Options > Modeler.

4. 3D Modeler Options Window

i) Click the Operation tab

Automatically cover closed polylines: Checked

ii) Click the Drawing tab

Edit property of new primitives: Checked

iii) Click the OK button

STEP : 3 Opening a New Project

To open a new project:

1. In an Ansoft HFSS window, select the menu item File > New.

2. From the Project menu, select Insert HFSS Design

Fig.4.2 Project Manager Window



STEP : 4 Set Solution Type

To set the solution type:

1. Select the menu item HFSS > Solution

2. Solution Type Window:

Choose Driven Terminal

Click the OK button

Fig.4.3 Solution Type Selection Window

STEP: 5 Creating the 3D Model

Set Model Units

Fig.4.4 Model Unit Window

To set the units

1. Select the menu item Modeler > Unit



2. Set Model Units

Select Units: mm

Click the OK button

STEP: 6 Set Default Material

To set the default material:

1. Using the 3D Modeler Materials toolbar, choose Select.

Fig.4.5 3D Modeler Materials toolbar 2. Select Definition Window:

FR4_eproxy

Click the OK.

Fig.4.6 Definition WindowSTEP: 7 Create Substrate

1) To create the substrate1:

i) Select the menu item Draw > Box

ii) Using the coordinate entry fields, enter the box position shown in window.

iii) Using the coordinate entry fields, enter the opposite corner of the box.

2) To set the name:



1. Select the Attribute tab from the Properties window.

2. For the Value of Name type: Sub1

3. Change the Color to Light Gray

4. Change the Transparency to 0.6

5. Click the OK button

Fig 4.7 Substrate Attributes window

To fit the view:

1. Select the menu item View > Fit All > Active Or press the CTRL+D key

Fig.4.8 Substrate Creation

STEP: 8 Create Ground

1) To create the Ground:



i) Select the menu item Draw >Rectangle

ii) Using the coordinate entry fields, enter the rectangle position shown in

window.

iii) Using the coordinate entry fields, enter the opposite corner of the rectangle

shown in Attributes window.

2) To set the name:


2. For the Value of Name type: GND

3. Change the Color to orange



Fig 4.9 Ground attribute window



Fig.4.10 Ground Creation

To fit the view:


STEP: 9 Create Patch

To create Patch

1. Select the menu item Draw > Rectangle

2. Using the coordinate entry fields, enter the rectangle position shown in

attributes window.

3. Using the coordinate entry fields, enter the opposite corner of the base

Rectangle shown in attributes window.

2) To set the name:


2. For the Value of Name type: GND

3. Change the Color to orange



Fig 4.11 Patch attributes window



Fig 4.12 Patch Creation

STEP: 10 Create Strip line

To Create Strip line



attributes window.


Rectangle as shown in attribute window.

To set the name:


2. For the Value of Name type: Strip line




Fig 4.13 Strip line attribute window

Select Patch + Strip line then right click Edit > Boolean > unite.

Fig 4.14 Strip line creation

To fit the view:

1. Select the menu item View > Fit All > Active View Or press the CTRL+D

key

STEP: 11 Create Slots

To create Slot1 and Slot2



attributes window.




Rectangle as shown in attribute window.

To set the name:


2. For the Value of Name type: Slot1 and Slot2.


Fig 4.15 Slot1 attribute window


Select Patch + Slot1 and Slot2 then right click Edit > Boolean >Substrate.



Fig 4.17 Slots creation

To fit the view:

1. Select the menu item View > Fit All > Active View Or press the CTRL+D

key

STEP: 12 Create Slot3

1) To create the Slot3:


ii) Using the coordinate entry fields, enter the rectangle position as shown in

attribute window.

iii) Using the coordinate entry fields, enter the opposite corner of the

rectangle as shown in attribute window.

2) To set the name:


2. For the Value of Name type: Slot3

3. Change the Color to red






Fig 4.19 Slot3 Creation

To fit the view:

1. Select the menu item View > Fit All > Active Or press the

CTRL+D key

STEP: 13 Create feed

1) To create the feed:


ii) Using the coordinate entry fields, enter the rectangle position as shown in

attribute window.

iii) Using the coordinate entry fields, enter the opposite corner of the rectangle

as shown in attribute window.

2) To set the name:




2. For the Value of Name type: feed

3. Change the Color to blue



Fig 4.20 Feed attribute window

Fig 4.21 Feed creation

To fit the view:


Step: 14 Creation of Radiation Box

Note: Radiation box is used to measure the far field radiation pattern and

is generally created at ¼ wavelength distance all around the patch.



1) To create the radiation box:

Select Draw> Region> Padding type > Percentage offset > 7.389 mm.

2) To set the name:


2. For the Value of Name type: radiation box

3. Change the Color to yellow

4. Change the Trasparency to 5.4


To fit the view:


ASSIGNING BOUNDARIES:

Step: 15 Assign a Perfect E boundary to the Ground

To select the feed:

1. Select the menu item Edit > Select > By Name

2. Select Object Dialog,

i) Select the objects named: Ground


To assign the Perfect E boundary

1. Select the menu item HFSS > Boundaries > Assign > Perfect E

2. Perfect E Boundary window

i) Name: PerfE_Ground

ii) Infinite Ground Plane: Unchecked




Fig.4.22 Perfect E Boundary window

Step: 16 Assign a Perfect E boundary to the Patch

To select the Patch:



i) Select the objects named: Patch


To assign the Perfect E boundary



i) Name: PerfE_Patch





Fig.4.23 Perfect E Boundary window

STEP: 17 Assign Radiation To Radiation Box:

To select the Radiation:



i) Select the objects named: Radiation


To assign the Radiation boundary



i) Name: PerfE_patch



STEP: 18 Create a Radiation Setup

To define the radiation setup

1. Select the menu item HFSS > Radiation > Insert Far Field Setup > Infinite

>Sphere

2. Far Field Radiation Sphere Setup dialog :



Select the Infinite Sphere Tab

i) Phi: (Start: 0, Stop: 90, Step Size: 90)

ii) Theta: (Start: -180, Stop: 180, Step Size: 2)

Click the OK button

Fig.4.24 Far Field Radiation Sphere Setup dialog

Step: 19 Assign Excitation

To select the object Source:



i) Select the objects named: Feed


Note: You can also select the object from the Model Tree

To assign lumped port excitation

1. Select the menu item HFSS > Excitations > Assign > Lumped Port

2. Place Feed in the Conducting Object list and Ground in the Reference

Conductor list

3. Click the OK button.



Fig.4.25 Lumped Port Reference Conductor For Terminal Window

STEP: 20 Creating Analysis Setup

To create an analysis setup

1. Select the menu item HFSS > Analysis Setup > Add Solution HFSS > Analysis

Setup > Add Solution Setup

2. Solution Setup Window:

1. Click the General tab:

Solution Frequency:10.15 GHz

Maximum Number of Passes: 10

Maximum Delta S: 0.02

2. Click the Options tab:

Enable Iterative Solver: Checked




Fig.4.26 HFSS Setup Window

STEP : 23 Adding a Frequency Sweep

To add a frequency sweep:

1. Select the menu item HFSS > Analysis Setup > Add Frequency Sweep

i) Select Solution Setup: Setup1


2. Edit Sweep Window:

1. Sweep Type: Interpolating

2. Frequency Setup Type: Linear Step

Start: 9.0GHz

Stop: 11.0GHz

Step size: 0.1GHz

Save Fields: Checked

4. Click the OK button.



Fig.4.27 Frequency Sweep Window

STEP: 24 Save The Project

STEP: 25 Model Validation

To validate the model:

1. Select the menu item HFSS > Validation

2. Click the Close button.

Analyze:

To start the solution process: Select the menu item HFSS > Analyze All.

Fig.4.28 Validation window



4.3 Conclusion

Using all the above steps we have successfully designed the

proposed antenna.



CHAPTER 5

FABRICATION PROCESS AND RESULTS

5.1 Introduction

During the past four decades, microstrip antennas have

attracted a great deal of attention due to their low profile, ease of fabrication, low

cost, and conformability. Inkjet-printed antennas using highly conducting patterns

can complement and extend the above-mentioned advantages to achieve modern,

clean, fast, and reliable antenna fabrication technologies. Moreover, the use of

nanoscale materials allows for the development of a new generation of modern

printed circuit antennas. Due to the ever-growing demands for printed RF circuits

and antennas to serve different emerging applications such as Radio Frequency

Identification (RFID), wireless sensors, portable health monitoring, and wearable

devices, several eager attempts from different research groups have been

conducted to investigate the use of conductive ink based on different nano-

structural materials to explore low-cost roll-to-roll production, improve wireless

connectivity, structural performance, and flexibility and to reduce the level of

environmental contamination

Fig.5.1 Antenna Fabrication



5.2 Design Flow Chart for Fabrication

Fig.5.2 Flow Chart for Fabrication

5.3 Antenna Measurement Instrumentation

Antenna measurement ranges are general-purpose installations and should

allow measurements over a large band of frequencies. Due to the reciprocity, the



direction of signal propagation does not matter and hence the AUT can be the

transmitting as well as the receiving antenna. The advantage of having the AUT as

the receiving antenna is that the data processing and antenna manipulation can

occur at one site. At short ranges, there may be RF transmission lines between the

towers. The source antenna may be a log-periodic antenna at lower frequencies, a

horn or reflector at higher frequencies.

5.4 TRANSMITTERS AND RECEIVERS

To make accurate pattern measurements, a sufficiently powerful transmitter

and a good receiver is needed. The transmitter is usually close to the source

antenna and is remote controlled. Also, the source antenna polarization is remote

controlled. The transmitter should have a stable frequency and a pure spectrum.

Stable signal allows the use of a narrow receiving bandwidth, which is

prerequisite for a sensitive receiver. Simple signal generators can be used in many

measurements but sophisticated sweeping frequency synthesizers are best for

demanding measurement applications.

The receiver should be sensitive, narrow-band to suppress

interfering signals, linear, and should have a dynamic range. Heterodyne receivers

dedicated for antenna measurements and Vector Network Analyzer (VNA)

systems modified for antenna measurements are available for demanding

measurements.

Often there is a reference antenna at the receiving site to tune the receiver if

the signal frequency drifts during the measurement. The reference antenna also

provides a phase reference. When measuring large signal level variations the

receiver may saturate. A precaution is to insert a known attenuation in the receiver

input path when the main beam peak is measured. Large bandwidth allows higher

data rates but at the cost of sensitivity can be improved by post detection

averaging but again the measurement speed suffers. Time per measurement point

and required angle resolution set also a limit for the speed of rotation.

5.5 DATA PROCESSING

Simple measurements can be made manually, but in more complex



measurements automation is an essential feature because there are large amounts

of data involved. The computer controls the transmitter, receiver and positioner.

The receiver output is fed to a conventional pattern potter, either a rectangular or

polar plotter, or it is converted to digital format and saved to computer memory.

Angle information is obtained from the synchronous. The

use of a computer permits many ways for processing and analyzing the data.

Different plots, e.g., three dimensional or constant contour presentations can be

produced. The measurements can then be compared to the theoretical results. It is

also possible to interpolate between the measured cuts. The power can be

integrated to get the directivity.

5.6 EQUIPMENT USED FOR MEASUREMENT

The equipments used for measurement at the place where project work is

carried out are as follows;

Scalar Network Analyzer, Hewlett Packard 8757E

Digital Pattern Recorder, Flam & Russell Inc-944 (version 2)

2-port Directional Bridge, Hewlett Packard 80027C

5.7 NETWORK ANALYZER

Network analysis is the process of creating a data model of the transfer and/or

impedance characteristics of linear network through stimulus response testing

over a frequency range of interest. At the frequency above 1MHz, lumped

elements actually become circuits, consisting of the basic elements and

parasitic depend on the individual device and its component geometric are

comparable to signal wavelength, intensifying the variance in the circuit

behaviour due to the device instruction.



Fig 5.3 Network analyzer kit

Network Analyzer combines the control of a computer called a controller, with an

accurate, versatile combination of measurement capabilities. It combines signal

source, test equipment, computer and display into a single system. It permits a

wide selection of microwave instruments to be made with a high degree

of accuracy.

The network analyzer provides a large dynamic range of up to 90db

and has an internal microwave swept frequency that will operate a wide range

of frequencies.

Analyzers have the ability to transmit, reflect or absorb incident power. They

can measure both the magnitude and the phase of the reflection and

transmission coefficients. They are capable of separating the reflected wave from

the incident wave.

Simultaneous displays of time and frequency domain are possible. Computer

control of the sequence of testing allows for wide flexibility in the control of both

equipment interaction and the level of data desired. Keyboard control of all the

operations allows data acquisition at various level of operation. The computer

allows for the labeling graphical displays. Due to the high speed operation of

internal computers, results can be considered as occurring in real time and fixture

discontinuities as shown in real time.



5.8 RETURN LOSS TEST SETUP

Equipment Required for Return Loss Measurement:

1) Synthesized Sweeper - 1

Model No. : 83752A

2) Scalar Network Analyzer - 1

Model No. : 83757E

3) HP Laser Jet Printer - 1

Model No. : JET1150

4) Detector - 1

Model No. : 85025A

5) Directional Coupler - 1

Model No. : 18131-10

6) Co-Axial - Waveguide Adapter - 2

Model No. : 18094-SF40



Fig 5.4 Return Loss Test Set Up

A: Antenna under Test

B: Directional Coupler Model No. 18131 -10

C: Coaxial Waveguide Adapter Model No. 18094

D: Detector Model No. 8502A

5.9 TEST PROCEDURE FOR RETURN LOSS MEASUREMENT

Connect the test equipment as shown in the fig.6.2

Switch on Network Analyzer and set the desired band of frequency and

sweep it over the band from 2GHz to 11GHz.

Calibrate the Network Analyzer by connecting standard short/open at the

end of the directional coupler. Set the Network Analyzer vertical scale

calibration at 10 dB/division.

Normalize the feeder cable loss & directional coupler to 0 dB.

Connect the directional coupler other end to the antenna under test.



Fig 5.5 Return Loss

Read the response in Network analyzer over the band which is the return

loss of the antenna.

Return loss may be plotted over the prescribed frequency band.

5.10 VSWR Measurement

The measurement of VSWR was carried out using a scalar

network analyzer in an anechoic chamber.

A scalar network analyzer consists of a sweep frequency

generator and display unit. The sweep oscillator is set to the frequency band

(Start, Stop and markers at required positions) of operation of the AUT. The

return loss of the AUT is measured by sing a two-hole directional coupler and is

sent to display unit. Also, a reference of the sweep is given to the display unit.

This enables the display unit to plot the return loss in dB at different frequencies

in the band of operation. The VSWR is calculated from the return loss.



Fig 5.6 VSWR

5.11 MEASUREMENT OF DIRECTIONAL PATTERN

Measurement of the directional pattern of the antenna reveals a lot about the

functioning of the antenna and gives an overview about its performance. The

pattern is plotted in both the horizontal as well as the vertical plane of the antenna

by using a transmitting antenna operating in the same frequency band of the AUT.

There are three outdoor antenna test ranges installed in

Astra Microwave products Limited. These are 22m, 120m, and 1km. The range

that was selected to perform the testing of the project antenna was the 120m

outdoor elevated range.



Fig 5.7 Block diagram of Antenna Test Set up

The transmitting signal is generated by a sweep oscillator at

the transmit antenna. The transmitted signal is approximately amplified with a

suitable gain to overcome the path losses that are especially prominent in the

microwave frequencies. The received signal is fed to a network analyzer and later

to the digital pattern recorder that plots the received pattern at various points.



Table 5.1 List of Equipments used in Test set up

SNO EQUIPMENT MODEL NO. QUANTITY

1 Synthesized micro sweeper E8257D 1

2 Spectrum Analyzer 8564EC 1

3 Azimuth over elevation positioner AE500 1

4 Positioner controller - 1

5 Positioner cables - 1

6 Digital pattern recorder

a) 80846 DELL Computer

b) Color monitor

c) Laser printer

d) Software Version No.

1.0.0.1

944E

1

1

1

7 Rotary joint - 1

8 Power Amplifier 8601A 1

Fig 5.8 test setup for radiation pattern, gain measurement



Fig 5.9 Radiation pattern of proposed antenna

5.12 GAIN MEASUREMENT

There are two basic methods that can be used to

measure the gain of an antenna: absolute gain and gain comparison techniques.

The absolute gain method requires no a priori knowledge of the transmitting or

receiving antenna gain. If the receiving and transmitting antennas are identical,



one measurement and use of the transmission formula is sufficient to determine

the gain. If the antennas are different, three antennas and three measurements are

required to formulate a set of three equations with three unknowns to determine

the gain of the AUT. In the gain comparison method pre calibrated Standard Gain

Antennas are used to determine the absolute gain of the AUT.

The gain in any direction is power density

radiated in direction divided by power density this would have been radiated at by

a loss less (perfect) isotropic radiator having the same total accepted input power.

If the direction is not specified, the value for gain is taken to mean the maximum

value in they provide useful and simple theoretical antenna patterns with which to

compare real antennas. An antenna gain of 2 (3 dB) compared to an isotropic

antenna would be written as 3 dBi. The resonant half-wave dipole can be a useful

standard for comparing to other antennas at one frequency or over a very narrow

band of frequencies. To compare the dipole to an antenna over a range of

frequencies requires an adjustable dipole or a number of dipoles of different

lengths. An antenna gain of 1 (0 dB) compared to a dipole antenna would be

written as 0 dBi.

5.13 TEST RANGE FACILITIES

There are three outdoor antenna test ranges installed in Astra Microwave Products

Limited with the following salient features.

Ranges: 3 outdoor ranges (22m,120m, and 1km)

Frequencies: 100 MHz to 18 GHz

Measurement type: amplitude

Dynamic ranges: 80 dB

Sensitivity: -124 dBm

Maximum size of the antenna 6m

Positioner: azimuth over elevation.



Two scalar and vector network analyzers test setups are

available with printer/plotter outputs to measure return loss, insertion loss,

isolation measurements, in sweep and CW frequency range of 0.01 to 20 GHz.

Fig.5.10 Fabricated Antenna Front View

5.14 CONCLUSION

The fabrication steps involved in the antenna design and the materials used for the

fabrication of microstrip patch array are discussed and the CAD views given for

fabrication are shown.



CHAPTER 6

CONCLUSION

For printed ring slot antenna with microstrip feedline, the

miniaturization of the radiating slot element can be achieved by loading additional

slots on both sides of the ring slot. By introducing the bottom transverse slot

orthogonal to the microstrip feed line and utilizing the extension part of the

microstrip line, multiband characteristics can be obtained. The fundamental

frequency of the proposed antenna can be adjusted independently, so it is easy to

meet the requirements of the antenna performance. The antenna prototype can be

applied to the microwave rectifier antenna system or active antenna system.



REFERENCES

[1] M. Ali, G. Yang, and R. Dougal, “Miniature circularly polarized rectenna with

reduced out-of-band harmonics,” IEEE Antennas Wireless Propag. Lett., vol. 5,

pp. 107–110, 2006.

[2] C. Y. D. Sim, M. H. Chang, and B. Y. Chen, “Microstrip-fed ring slot antenna

design with wideband harmonic suppression”, IEEE Trans. Antennas Propagat.,

vol. 62, no. 9, pp. 4828–4832, Jun. 2014.

[3] A. F. Sheta, “A novel H-shaped patch antenna,” Microw. Opt. Technol. Lett.,

vol. 29, no. 1, pp. 62–66, Apr. 2001.

[4] J. Y. Park, S. M. Han, and T. Itoh, “A rectenna design with harmonic rejecting

circular-sector antenna,” IEEE Antennas Wireless Propag. Lett., vol. 3, pp. 52–54,

2004.

[5] H. Kim and Y. J. Yoon, “Microstrip-fed slot antennas with suppressed

harmonics,” IEEE Trans. Antennas Propagat., vol. 53, no. 9, pp. 2809–2817, Sep.

2005.

[6] Y. J. Ren, M. F. Farooqui, and K. Chang, “A compact dual-frequency

rectifying antenna with high-orders harmonic-rejection,” IEEE Trans. Antennas

Propagat., vol. 55, no. 7, pp. 2110–2113, Jul. 2007.

[7] S. il Kwak, J. H. Kwon, D. U. Sim, K. Chang, and Y. J. Yoon “Design of the

printed slot antenna using wiggly-line with harmonic suppression,” IEEE

Antennas Wireless Propag. Lett., vol. 9, pp. 741–743, 2010


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