Microwave Antennas Play a Major Role in Today's Wireless Communication Networks - Management Assignment Help

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ABSTRACT
Microwave antennas play a major role in today's wireless communication networks. This thesis is based on the use of various kinds of defected ground structure techniques to design a compact rectangular patch for multiband applications. This work introduces five ways to design and simulate the multiband antennas. A novel rectangular patch antenna with transmission feed for X band application is presented in the first section. The resonant frequencies are shifted by varying the length of the patch using transmission line feeding, and single resonant modes of the patch antenna is simulated. The rectangular patch antenna has an operating frequency of 7.3 GHz with return loss of -26.02 dB. a novel ladder defected ground structure (LDGS) has been proposed to work at dual-band applications. The dual bands are obtained by accommodating the dimensions of slotted ladder DGS in ground. The 10 dB return loss bandwidth percentage of simulated LDGS are 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz) The gain of dual band antennas are between 6 to 8 dB, the LDGS has improved the 10 dB return loss bandwidth, radiation characteristics and max gain. The fabricated antenna is tested experimentally by cross verifying the simulated results. The measurements have been carried out using vector network analyzer in anechoic chamber.
CONTENTS
ChapterNoDescription Page No.
ABSTRACTvii
Chapter 1Introduction01
1.1Methodology 01
1.1.1 Electrmagnetic Simulation Software 01
1.2 Problem Statement 01
1.3 Objective of the thesis 02
1.4 Scopes 03
1.5 Significant of Research 03
1.6 Organization of thesis 04
Chapter 2 Literature Survey
2.1Electromagnetic Spectrum Bands 07
2.2Antenna parameters 10
2.2.1Bandwidth 10
2.2.2Gain 11
2.2.3Radiation Pattern 11
2.2.4Input Impedance 12
2.2.5Directivity 12
2.2.6Polarization and Polarization mismatch 12
2.2.7Beamwidth 13
2.2.8Power density 13
2.3VSWR 13
2.3.1Return loss 14
2.4Wireless Communications 14
2.5Types of Patch Antennas 15
2.6Basic Microstrip Structure 17
2.6.1Advantages 20
2.6.2Disadvantages 21
2.6.3Applications 21
2.7Defected Ground Structures 21
2.8Literature Review 24
2.9 Summary 39

Chapter 3 The analysis of Rectangular Patch Antenna
for X Band Applications
3.1Introduction 41
3.2 Flowcahart of methodology 41
3.3Design of Rectangular Microstrip Antenna42
3.4Design of Circular Microstrip Antenna43
3.5Design of Triangular Microstrip Antenna45
3.6Simulation of Circular Microstrip Antenna47
3.7Simulation of Triangular Microstrip Antenna48
3.8Simulation of Rectangular Microstrip Antenna50
3.9Conclusions59
Chapter 4 The analysis of ladder Shaped DGS for Dual Band
Applications
4.1Introduction 61
4.2The analysis of circular Patch
antenna with ladder shaped DGS63
4.2.1circular Patch antenna with ladder
Shaped Defected Ground Structure63
4.2.2circular ring Patch antenna with ladder
Shaped DGS67
4.2.3The annular ring Patch antenna with ladder Shaped DGS for Dual Band Applications69
Chapter 5 Conclusions and Future scope
5.1 Conclusions 107
5.2 Future scope 108
References 110
List of Figures
Figure NoName of the Figure Page No
Fig.2.1Gain of an antenna11
Fig.2.2Radiation pattern of an antenna
(a) Rectangular plot12
(b) Polar plot12
Fig.2.3Different types of polarization13
Fig.2.4Beamwidth of an atenna13
Fig.2.5VSWR of an antenna14
Fig.2.6Return loss of an antenna14
Fig.2.7Different shapes of Microstrip Patch antenna15
Fig.2.8Microstrip patch antennas with feed from side16
Fig.2.9General Rectangular microstrip patch antenna17
Fig.2.10Basic Microstrip antenna Structure18
Fig.2.11Thickness of substrate vs frequency plot20
Fig.2.12Different geometrics of DGS used in the literature23
Fig.3.1 Flowchart to design rectangular patch antenna 42
Fig.3.2 Basic Rectangular Patch antenna model 42
Fig.3.3Geomentry of Circular Microstrip antenna44
Fig.3.4Triangular patch antenna with field distributions46
Fig.3.5Circular Microstrip Patch antenna47
Fig.3.6Return loss of Circular Patch antenna47
Fig.3.7VSWR of Circular Patch antenna48
Fig.3.8Maximum peak gain of Circular Patch antenna48
Fig.3.9Triangular microstrip Patch antenna49
Fig.3.10Return loss of Triangular Patch antenna49
Fig.3.11VSWR of Triangular Patch antenna50
Fig.3.12Maximum gain of Triangular Patch antenna50
Fig.3.13Rectangular microstrip antenna with insert feed Line51
Fig.3.14Return loss of Rectangular Patch antenna52
Fig.3.15Comparison of return loss between different materials
used for Rectangular Patch antenna53
Fig.3.16Parametric analysis on length (L1) of Rectangular Patch
antenna54
Fig.3.17Parametric analysis on width (W1) of Rectangular Patch
antenna55
Fig.3.18VSWR of Rectangular Patch antenna55
Fig.3.19Maximum gain of Rectangular Patch antenna56
Fig.3.20Radiation characteristics of Rectangular Patch Antenna 56
Fig.3.21Field distributions of Rectangular Patch antenna (a) E field
(b)H field (c) J field58
Fig.3.22Comparison of return loss between Rectangular ring,
Rectangle and Square Patch antennas59
Fig.4.1circular Patch antenna with ladder DGS Slot64
Fig.4.2Retrn loss values of circular Patch antenna with
Ladder DGS 65
Fig.4.3VSWR of circular Patch antenna with ladder DGS
Etching on Ground Plane66
Fig.4.4Radiation Characteristics of circular Patch antenna
with ladder DGS slot (a) E Plane (b) H Plane66
Fig.4.5Peak Gain value of circular Patch antenna with
Ladder DGS Etching on Ground Plane67
Fig.4.6circular Patch antenna with T Sape Slot Etching On Ground Plane68
Fig.4.7Return loss of Rectangular Patch antenna with T Shaped
Slot on Ground Plane68
Fig.4.8VSWR of rectangular patch antenna with T Shape Slot on Ground Plane69
Fig.4.9Radiation Pattern of Rectangular Patch antenna with T
Shaped DGS (a) E Plane (b) H Plane69
Fig.4.10Peak Gain of Rectangular Patch antenna with T Shaped
Slot on Ground Plane70
Fig.4.11Rectangular Patch antenna with U Shaped Slot on Ground Plane71
Fig.4.12Comaparision of return loss for Rectangular Patch antenna between with and without U shaped DGS71
Fig.4.13VSWR of Rectangular Patch antenna with U Shaped DGS72
Fig.4.14Radiation Characteristics of Rectangular Patch antenna
with U shaped DGS antenna at (a) E Plane at 5.7GHz
(b) H Plane at 5.7GHz (c) E Plane at 8.8GHz
(d) H Plane at 8.8GHz73
Fig.4.15Field Distributions of Rectangular Patch antenna with U shaped DGS (a) E Field (b) H Field (c) J Field 74
Fig.4.16The Maximum peak Gain values of Rectangular Patch
antenna with U shaped DGS at (a) 5.7GHz (b) 8.8GHz74
Fig.4.17The rectangular patch antenna with different types of
DGS (a) antenna 1 (b) antenna 2 (c) antenna 375
Fig.4.18Rectangular patch antena with single slot antenna 176
Fig.4.19Parametric analysis on length (L4) of antenna 177
Fig.4.20Parametric analysis on width (W4) of antenna 177
Fig.4.21VSWR of Rectangular Patch antenna with I sape slot78
Fig.4.22Rectangular Patch antenna with T shape slot78
Fig.4.23Parametric analysis on width (W6) of antenna 279
Fig.4.24VSWR of T shaped slot on ground plane of antenna 2 79
Fig.4.25Rectangular Patch antenna with dumbbell shaped DGS 79
Fig.4.26Comaparison of return loss for Rectangular Patch antenna between with and without Dumbbell80
Fig.4.27Prototype of Rectangular Patch antenna with dumbbell
defected ground structure
(a) front view (b) back view80
Fig.4.28Testing of Rectangular Patch antenna with dumbbell DGS
on Vector Network Analyzer81
Fig.4.29Comparison between simulated and measured reflection coefficient of Rectangular Patch antennawith dumbbell
DGS81
Fig.4.30Comparison between simulated and measured VSWR of Rectangular Patch antenna with dumbbell DGS82
Fig.4.31Radiation pattern of Rectangular Patch antenna with
dumbbell DGS antenna for frequency of (a) 5.9 GHz
(xz plane) (b) 5.9 GHz (yz plane) (c) 7 GHz (xz plane) (d) 7 GHz (yz plane) (e) 8.7 GHz (xz plane) (f) 8.7 GHz yz plane) (g) 9.7 GHz (xz plane) (h) 9.7 GHz (yz plane)83
Fig.4.32The gain total of Rectangular Patch antenna with dumbbell
DGS at operating frequencies (a) 5.9 GHz (b)7 GHz (c) 8 GHz
(d) 9.7 GHz 85
Fig.4.33The maximum field distribution of Recangular Patch antenna with dumbbell DGS at (a) E field (b) H field85
List of Tables
Table NoName of the Table Page No
Table 2.1Electomagnetic Spectrum Bands08
Table 2.2Wireless Communicatin Services and their frequency09
bands
Table 3.1Dimensions of the proposed Rectangular patch52
antenna
Table 3.2Simulated Results of Rectangular Patch antenna53
Table 3.3Return loss for different materials used in the design
of Rectangular Patch antenna54
Table 3.4Comaparative Study of different Microstrip Patch
antennas 59
Table 4.1Dimensions of Rectangular Patch antenna
with U shaped DGS71
Table 4.2 Dimensions of Rectangular Patch antenna with
Dumbbell DGS76

LIST OF ACRONYMS
VLFVery Low Frequency
LFLow Frequency
MFMedium Frequency
HFHigh Frequency
VHFVery High Frequency
UHFUltra High Frequency
GSMGlobal System for Mobile
GPSGlobal Positioning System
DCSDigital Communication System
PCSPersonal Communication System
DVBDigital Video Broadcasting
RFRadio Frequency
RFIDRadio Frequency Identification
IMTInternational Mobile Telecommunication
UMTSUniversal Mobile Telecommunication Systems
ISMIndustrial,Scientific and Medical applications
UWBUltra -Wide Band
FCCFederal Communication Council
FEMFinite Element Method
MOMMethod of Moments
FDTDFinite Differential Time Domain
HFSSHigh Frequency Structure Simulator
HFSS-IEHigh Frequency Structure Simulator- Integral Equation
CSTComputer Simulation Technology
IE3DIntegral Equation Three - Dimensional
PCBPrinted Circuit Board
VNAVector Network Analyzer
VSWRVoltage Standing Wave Ratio
FR4Fire Resistance 4
LPLinear Programming
SNLPSequential Non-Linear Programming
SARSpecific Absorption Rate
PBGPhotonic Band Gap
EBGElectromagnetic Band Gap
DGSDefected Ground Structure
FDGSFractal Defected Ground Structure
RS-DGSRectangular-Shaped Defected Ground Structure
TDGST-Shaped Defected Ground Structure
WLANWireless Local Area Networks
WBANWireless Body Area Nteworks
WiMAXWorldwide Interoperability for Microwave Access
MIMOMultiple Input and Multiple Output
TETransverse Electric
TMTransverse Magnetic
TEMTransverse Electromagnetic
MSPAMicrostrip Patch Antenna
RADARRadio Detection And Ranging
PCBPrinted Circuit Board
MICMicrowave Integrated Circuits
ZORZeroth Order Resonant
E FieldElectric Field
H FieldMagnetic Field
J FieldSurface Current Field
CPCircular Polarization
CPWCoplanar Waveguide
PECPerfect Electric Conductor
SIWSubstrate Integrated Waveguide
Co PolCo Polarization
Cross PolCross Polarization
LPFLowpass Filter
HPFHighpass Filter
BPFBandpass Filter
EMCElectromagnetic Compatibility
SRRSplit Ring Resonator
RCSRRRectangular Codirectional Splt Ring Resonator
OCSRROpen Complementary Split Ring Resonator
SISStepped Impedance Stubs
IEEEInstitute of Electrical and Electronics Engineers
HTSHigh Temperature Superconducting
CNCCommunication Network and Computing
LIST OF SYMBOLS
Symbol Description
?r Dielectric permittivity of the substrate
?e Effective dielectric constant
fr Resonating frequency
fo Operating frequency
h Height of the substrate
C Velocity of the light
L Length of the rectangular patch
Le Effective length of the patch
W Width of the patch
We Effective width of the patch
Lg Length of the ground plane
Wg Width of the ground plane.
S Each side of triangle
Se Effective side length of triangle
S11 Return loss

CHAPTER 1
INTRODUCTION
1.1 Introduction
The design methodology plays a key role in synchronization of simulated and fabricated antenna results. The parametric analysis of proposed defected ground structure designed at a particular cutoff frequency is carried out using ANSYS High Frequency Structure Simulator (HFSS). The final optimized structure is fabricated using photolithography and by using Printed Circuit Board (PCB), proto typing machine "MITS Auto Lab". The fabricated antenna is characterized using Vector Network Analyzer (VNA).
The defected ground structure antennas have to be fabricated in low cost, easily available, thermally stable substrates. The substrate used for the fabrication is FR4 epoxy material (dielectric constant=4.4) of thickness 1.6 mm. By using FR4 epoxy material, the high performance and quality designs are obtained. Due to high power handling capability, microstrip patch resonators are commonly used for the design of microstrip defected ground structure. Another important advantage of using the patch resonator is the lower conductor loss as compared to the microstrip filter using line resonators. Based on the application of defected ground structure, the patches may have different shapes. Some typical shapes are triangular, circular, ring, rectangular etc.
1.1.1 Electromagnetic Simulation Software
The simulations of different defected ground structures are performed using ANSYS High Frequency Structure Simulator (HFSS). ANSYS HFSS is the globally accepted EM simulation software, which uses full wave Finite Element Method to compute the behavior of high frequency components. HFSS is used to extract the performance parameters of the microstrip structures such as S, Y and Z parameters, to visualize the 3D EM fields and also used to analyze the group delay, VSWR. The effect of various filter parameters can be effectively studied using the optimization tool available with HFSS. Among the different boundary schemes of HFSS, the radiation boundary and perfect electric conductor boundary is commonly used in the proposed work. The scalar and vector representation of E, H and J values demonstrate the behavior of the filters in the passband and stopband characteristics.
1.2 Problem Statement
The microstrip patch antennas (MSPA) is a essential device in the modern communication and radar systems. The provocative characteristics of MSPA are low cost, easy to design and conformability of the object. However the multi-band antennas has widely used in wireless and satellite communications. The different shape of defected ground structures (DGS) at ground plane to improve the impedance bandwidth, integration of microstrip lines and reduce the cross polarization.
1.3 Objective of the thesis
The objective is,
To design and simulate the rectangular Patch antenna with defected ground structure slot. To compare and verify different parameters of the designed antenna with measured values.
The defected ground structure plays a important role in communications. The proposed antennas are used in different applications like mobile communications, military, satellite, television and radar applications. In the communication field, cellular radio is widely accepted and popular now a days than the conventional wired telephony. RF and microwave antennas are very commonly used in these systems to filter out the unwanted frequencies, while permitting wanted signals without any attenuation. Cellular communication needs DGS with specific performance characteristics in base stations as well as mobile handsets. The defected ground structure is mainly used to improve the bandwidth, more number of channels are communicated through this channels. The overall dimensions of the antenna is also minimized, low cost and high gain.
The Cost of the raw material used in real time fabrication is very important while designing defected ground structure for commercial applications. Thus FR4 substrate is a suitable choice for its low cost, easy availability and light weight. Using this substrate, defected ground structure with good selectivity and wide stopband is realized. The main objective of this research work is the design and development of such high performance microstrip defected ground structure antenna , which are fabricated with FR4 substrate of thickness 1.6 mm. Different techniques are adopted for the design like U shape, fractal shape, dumbbell shape and T shaped defected ground structures.
1.4 Scopes
The rectangular patch with geometric series defected ground structure (DGS) has been proposed. The proposed antenna has operated at multi band operating frequencies. The multi band has wide impedance bandwidth and maximum gain at operating frequencies. The co polarization and cross polarization of E plane and H plane are measured, the electric field , magnetic field and current distributions of rectangular patch antenna is measured. The radiation patterns are observed at is 450 and is 900 in xy, yz and zx plane for three resonance bands. The co and cross polarization has presented and cross polarization is found below 40 dB at one plane of each angle and operating frequency. The measurement has been carried out with simulation results of return loss of proposed antenna.
1.5 Significant of Research
In recent years, there have been several new concepts applied to distributed microwave circuits. One such technique is defected ground structure or DGS, where the ground plane metal of a microstrip circuit is intentionally modified to enhance performance. The name for this technique simply means that a “defect” has been placed in the ground plane, which is typically considered to be an approximation of an infinite, perfectly-cting current sink. A ground plane at microwave frequencies is far removed from the idealized behavior of perfect ground. Although the additional perturbations of DGS alter the uniformity of the ground plane, they do not render it defective. DGS Element Characteristics.
The basic element of DGS is a resonant gap or slot in the ground metal, placed directly under a transmission line and aligned for efficient coupling to the line. The several resonant structures that may be used. Each one differs in occupied area, equivalent L-C ratio, coupling coefficient, higher-order responses, and other electrical parameters. The equivalent circuit for a DGS is a parallel-tuned circuit in series with the transmission line. The input and output impedances are that of the line section, while the equivalent values of L, C and R are determined by the dimensions.
1.6 Organization of thesis
Chapter 1 : Introduction
Chapter 2 : Literature Survey
Chapter 3 : The analysis of Rectangular patch antenna for X band applications
Chapter 4 : The analysis of U shaped DGS for dual band and dumbbell shaped DGS for multiple band applications.
Chapter 5: Design of rectangular antenna with fractal defected ground structure for dual band applications.
Chapter 6: Design of H shape patch antenna with T shape slotted defected ground structure for dual band applications.
Chapter 7: Conclusions and Future Scope
Chapter 1 Gives information about the theme and objectives of the thesis.
Chapter 2 Covers the frequency bands of EM spectrum and their applications. Gives information about the literature survey and covers the introduction about the microstrip patch antenna and its advantages and applications.It also describes about different antenna parameters.
Chapter 3 Dedicated to the step wise design procedure of the rectangular patch antenna using HFSS and their corresponding calculations, equations and simulation results.
Chapter 4 Deals with the design of rectangular patch antenna with U shaped defected ground structure using HFSS. Verifying the characteristics of antenna parameters in various ways and Parametric analysis of the antenna . The analysis and the description of simulation results are described.
Includes the rectangular microstrip patch antenna with dumbbell shaped defected ground structure. The return loss and VSWR values were measured using Vector Network Analyzer. Simulation results and measured results are verified.
Chapter 5 Includes the rectangular microstrip patch antenna with fractal shaped defected ground structure. Verifying the characteristics of antenna parameters in various ways. Parametric analysis of antenna is shown. The analysis and the description of simulation results and measured results are described.
Chapter 6 Includes the H shaped microstrip patch antenna with T shaped defected ground structure. Verifying the characteristics of antenna parameters in various ways. Parametric analysis of antenna is shown. The analysis and the description of simulation results and measured results are described.
Chapter 7 Discussed the conclusions of microstrip antenna with different defected ground structures and discussed about the future scope of the patch antenna with defected ground structures.
CHAPTER 2
Literature Survey
2.1 ELECROMAGNETIC SPECTRUM BANDS
In communication systems antennas are very important components and they are defined as the devices which are used to send a signal i.e.., RF signal which traverses a path from conductor to electromagnetic wave in free space. Antennas work on a property called ‘reciprocity’ i. e, antennas work with the same characteristics irrespective of its function as transmitter or receiver. Antennas which are used are commonly resonant antennas which operates efficiently at specific frequency band. An antenna is generally fed with the signal and antenna emit radiations which are plotted graphically and this plotting is called radiation pattern. The electromagnetic spectrum covers all frequencies of electromagnetic radiation and range from 1 Hz to 1025 Hz. Later these frequencies are divided into different bands and different names. The Ancient Greeks observed travel of light as straight lines and analyzed the reflection, refraction like light properties. William Herschel discovered infrared radiation in 1800, Johann Ritter worked on electromagnetic spectrum and identified ultraviolet radiation in 1801. The electromagnetic radiation to electromagnetism was first connected by Michael Faraday in 1845 and noticed that light polarization is analogous to magnetic field.
In 1860's James Clerk Maxwell discovered that the electromagnetic waves travel at the speed of light and he developed four partial differential equations for electromagnetic field. In 1886, Heinrich Hertz attempted to prove the theoretical equations of Maxwell and tried to generate radio waves and found that the radio waves travel at the speed of light and proposed the properties of reflection and refraction. He generated the microwaves and measured its properties and paved the way for the invention of wireless communications such as wireless telegraphy and radio. During an experiment in 1895, Wilhelm Rontgen noticed an emission of new type of radiations and he named these as X-rays. He found that these rays were able to travel through biological substances and get reflected by any denser matter, and thus it can be used for medical analysis of human body. The end portion of electromagnetic spectrum was occupied with Gamma rays. In the year 1900, the French physicist, Paul Ulrich Villard, during the experimentation on the radio activity of Radium, noticed a new type of radiation. As per his theory, these radiations are similar to Alpha and Beta particles, but can penetrate more powerfully. In 1903, Ernest Rutherford named these radiations as Gamma rays. Afterwards, in 1910 William Henry Bragg established that these rays also come under electromagnetic radiation and are not particles as believed earlier.
Antennas have wide range of applications in the electromagnetic spectrum. In order to avoid the congestion during the communication process, the frequency bands are allocated for different applications, as mentioned in Table 2.1 and Wireless Communication Services and their frequency bands, as mentioned in Table 2.2. The frequency allocation helps reduce the interference from multiple users.
Table 2.1 Electromagnetic Spectrum Bands
Band Designation Frequency range Usage
VLF 3-30KHz Long distance telegraphy and navigation
LF 30-300 KHz Aeronautical navigation services, Radio broadcasting, Long distance communication
MF 300-3000 KHz Regional broadcasting, AM radio
HF 3-30MHz Communications, broadcasting, surveillance, CB radio
VHF 30-300 MHz Surveillance, TV broadcasting, FM radio
UHF 30-1000MHz Cellular communications
1-2 GHz Long range surveillance, Remote sensing
L S 2-4 GHz Weather detection, Long range tracking
C 4-8 GHz Weather detection, Long-range tracking
X 8-12 GHz Satellite communications, missile guidance, mapping
Ku 12-18 GHz Satellite communications, Altimetry, high resolution mapping
K 18-26 GHz Very high resolution mapping
Ka 26-40 GHz Airport surveillance
Table 2.2 Wireless Communication Services and their frequency bands
Name of the Wireless Communication Service Allocated frequency band Commonly used Antenna
Digital Video Broadcasting (DVB-H) 470MHZ-702MHz Compact printed Antennas
Radio Frequency Identification (RFID) 865-868MHz,
2.446-2.454GHz Loops, Folded-F, Patch and Monopole
Global System for Mobile (GSM 900) 890MHz-960MHz Dipole, patch arrays and Monopoles.
Global Positioning System (GPS1400, GPS1575) 1227MHz -1575MHz, 1565MHz-1585MHz Microstrip patch or bifilar helix
Digital Communication System (DCS 1800) 1710MHz-1880MHz Dipole or patch arrays in base stations.
Monopoles, sleeve dipoles and patch in mobile handset
Personal Communication System (PCS 1900) 1850MHz-1990MHz International Mobile Telecommunication-2000 (3G IMT-2000) 1885MHz-2200MHz Universal Mobile Telecommunication Systems (UMTS 2000) 1920MHz-2170MHz Industrial ,Scientific and Medical(ISM 2.4, ISM 5.2,
ISM 5.8) 2400MHz-2484MHz,
5150MHz-5350MHz,
5725MHz-5825MHz Ultra Wide Band (UWB) communication 3.1GHz-10.6GHz Planar printed antennas, Horn Antennas
The microwaves are radio waves with frequency ranging from 300 MHz to 300 GHz. The wavelength decreases from one meter to one millimeter when frequency increases from 300 Hz to 300 GHz. The microwave technology has been used in a wide range of applications such as telecommunications, sensing and imaging applications. The areas of applications are categorized as but not limited to radar, defense, security, food processing, point to point communication, satellite, cellular technology etc. All these applications fall in the frequency range from 300 MHz to 300 GHz.
2.2 Antenna Parameters:
For designing an antenna, consider few terms and these terms are specified and defined .
2.2.1 Bandwidth:
The range of frequencies at which an antenna operates with required characteristics is known as bandwidth. The bandwidth is measured in terms of hertz for which the SWR is in the ratio 2:1. This bandwidth is calculated in terms of percentage with the help of Centre frequency of the bandwidth range frequencies. The formulae to calculate fractional bandwidth percentage is given by an equation ( 2.1 ).
QUOTE (2.1)
The above formula terms are,
fh - highest frequency
fl - lowest frequency
fc - Centre frequency
From the equation (2.1) bandwidth is directly proportional to frequency. The bandwidth of different antennas varies considerably based on the design methodologies.
2.2.2 Gain:
Gain of an antenna is not a physical quantity that can be defined. It is the ratio of input and output of the antenna under consideration. The gain of an antenna is determined by comparing the gain of a standard antenna. These antennas are called reference antennas,the reference antennas are isotropic antenna and half wave dipole antenna.
These antennas are considered as reference antennas as they radiate equally in all directions. The energy that propagates through the antenna is maximum when an antenna has isotropic antenna characteristics. Comparative methods are used to calculate the gain of a particular designed antenna. This testing is done with the help of the reference antenna and this is done using two antennas. On the other hand there is another method used to calculate the gain of an antenna, in this method three antennas are used which are placed at a particular distance.

Fig 2.1 Gain of an antenna
2.2.3 Radiation pattern:
An antenna is generally fed with the signal and antenna emits radiations which are plotted graphically. This plotting of radiation characteristics is called radiation pattern. The graphical plot of radiation pattern is done in two ways i.e.., rectangular plot and polar plot, examples of these two plotting are shown in Fig. 2.2 .

(a) (b)
Fig 2.2 Radiation pattern of an antenna
(a) Rectangular plot (b) Polar plot
The rectangular plot is a general plotting that is done with frequency and other antenna terms and is simple to study. The polar plot specifications are bit different from rectangular plot. This polar plot is classified into two types i.e.., linear and logarithmic plotting. By plotting the analytical values in the graph, lobes are formed in the polar plot and the losses in the designed antenna is observed by the number of side lobes and back lobes formed. Generally plot voltage in the polar plot rather than other parameters like power. The voltage is plotted in the form of dB. The example of polar plot is shown in Fig. 2.2 (b).
2.2.4 Input impedance:
Generally a connecting wire which is a conductor to connect transmitting source to antenna. The impedance of this antenna and the conducting wire must be same and it is generally required to be as 50 ohms. If the impedance value is other than 50 ohms then an impedance matching circuit is used in the antenna set up.
2.2.5 Directivity:
The total energy of the transmitted and received signal of an antenna in particular direction is known as directivity. When an antenna transmits energy in all directions equally then that is known as Omnidirectional antenna.
2.2.6 Polarization and polarization mismatch:
The formation of the electric field of an electromagnetic wave is called polarization. Polarization is generally known as elliptical polarization and it is of two types namely linear polarization and circular polarization .

Fig. 2.3 Different types of polarization
When the alignment of antennas is not done properly then the setup is said to have polarization mismatch and this leads to loss of energy from the antenna set up. To overcome this problem an impedance matching circuit is placed in the antenna design.
2.2.7 Beamwidth:
The performance of an antenna decreases when the number of side lobes increases, that is the antenna radiates in the unwanted directions rather than the desired direction. In radar applications,the beamwidth helps to make a difference between the two or more sources within that vicinity.

Fig. 2.4 Beamwidth of an antenna
2.2.8 Power density:
Every parameter of the antenna is generally measured at the far field. The power pattern is obtained from the radiated antenna and measured to average power density the antenna depends on the direction. The researchers have proposed constant radius extends into the far field.
2.3 VSWR:
The VSWR is the ratio of the maximum power transmitted in the desired direction at the output port to minimum power transmitted at the input port. The goal is to have maximum power transfer between input and output ports. This happens only if the ohmic resistance Zin is matched to the transmitter ohmic resistance, Zs .

Fig. 2.5 VSWR of an antenna
2.3.1 Return loss:
The mismatch can be expressed in different ways and the logarithmic measurement of mismatch is known as return loss. It is the comparison of power fed and power reflected by an antenna. Return loss is SWR dependent. The return loss of the antenna is measured from the input and output signals of the sources.

Fig. 2.6 Return loss of an antenna
2.4 Wireless communications:
During 1940's there was a step by step development in the antenna technology. This is mainly due to the principles of Maxwell. Later on it is related to radiating wires. There are different types of antennas in the modern technology. The present generation of Antenna technology works under microwave sources like klystron and magnetron introduced recently.
In nineteenth century antenna technology had improved to a great extent, the impedance and bandwidth ranges for different antennas were also changed considerably. Antenna was first invented by an Italian electrical engineer Marconi in 1906 and his work provided a path for many future developments till today in the area of communication and he also formulated a law which is famously known as Marconi law. 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 antenna design to meet the demands of the present day technology. All the developments in the antennas are mainly depended 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 to decrease the antenna size.
2.5 Types of Patch Antennas
The microstrip patch antennas are different types depending on the characteristics of the application. For the microwave and millimeter wave frequencies, the different types of antennas are rectangular patch, square patch, and circular patches shown in Fig. 2.7.

Fig. 2.7 Different shapes of microstrip patch antenna
The substrate is likewise imperative, temperature, humanity and alternative coincidental spectrum of performing to be treated. Thickness of the substrate has a massive consequence on the resonant frequency and bandwidth BW of the antenna. Bandwidth of the microstrip antenna will be incrementing of substrate thickness but with restraints, otherwise the antenna will stop resonating at resonating frequencies.

Fig. 2.8 (a, b) Microstrip patch antenna with feed from side
The location of the feed point of the patch is reviewed in particular for Impedance Matching. The impedance of the patch is given by equation ( 1.2 )
( 2.2 )
The characteristic impedance of the transition section should be:
( 2.3 )
The width of the transition line is computed from
( 2.4 )
The width of the 50? microstrip feed can be found using the equation ( 2.5 ),
( 2.5 )
The length of the strip can be found from
( 2.6 )
The length of the transition line is quarter the wavelength
( 2.7 )

Fig. 2.9 General Structure of Rectangular Microstrip patch antenna
2.6 BASIC MICROSTRIP STRUCTURE
The basic structure of a microstrip antenna is depicted in Fig. 2.10. A conducting microstrip line of width W, having its thickness t is placed on the top of the dielectric substrate. The dielectric substrate has its relative dielectric constant ?r , and thickness h is used as shown in Fig. 2.10. The bottom plane of the substrate is the conducting ground plane.

Fig.2.10 Basic Microstrip antenna Structure
The fields in the microstrip antenna does not support pure TEM wave due to its inhomogeneous nature (because the fields in microstrip antenna extend within air above the microstrip and dielectric below). Thus due to the presence of the two guided media in the microstrip, (air and the dielectric substrate), quasi-TEM approximation is commonly used, and its wave propagation velocity depends not only on the properties of the material such as permeability and the permittivity, but also on its physical dimensions. The transmission characteristics of the microstrip mainly depend on two important parameters namely, effective dielectric constant, ?re and the characteristic impedance, ZOC. The effective dielectric constant depends on the relative permittivity of the substrate, width, w of the microstrip line and the thickness of the dielectric substrate. The characteristic impedance of the microstrip line depends not only on the line width w and thickness h, but also on the effective dielectric constant of the microstrip. The closed form expressions for the calculation of ?re and ZOC are in equation ( 2.8 ) to equation ( 2.11 ).
For w/h?1,
?re= QUOTE ( 2.8 )
QUOTE ( 2.9 )
Where ? is the free space wave impedance and it’s value is 120????
For w/h QUOTE ,
?re= QUOTE ( 2.10 )
QUOTE ( 2.11 )
The guided wavelength, QUOTE of quasi TEM mode of the microstrip antenna is given by equation ( 1.12 )
QUOTE ( 2.12 )
Where QUOTE is the free space wave length at 3 dB cut off frequency
The substrate thickness, h has an important role in defining the performance characteristics of an antenna. The cutoff frequency versus thickness of the FR4 substrate is shown in Fig. 1.11. As the value of h decreases, the cutoff frequency also reduces and thus compactness of an antenna is achieved. Thus conclude that by reducing the thickness of the substrate, the size miniaturization of an antenna can be achieved.

Fig. 2.11 Thickness of substrate vs frequency plot
2.6.1 Advantages
The main advantages of the microstrip patch antennas are given below:
Low volume and compact size.
Low profile which can be easily designed to be conformal in a surface.
Less fabrication cost and easy to fabricate, so they can be manufactured in large quantities.
The microstrips are useful at linear and circular polarizations with same size and shape.
The microstrip patch antennas are integrated very easily with microwave integrated circuits (MICs).
Capable of multiple frequency operations.
2.6.2 Disadvantages
Narrow bandwidth which are only in MHz and sometimes in GHz range.
Low efficiency of radiation from patch.
Low Gain due to insufficient slots.
Extraneous radiation from feeds and junctions
2.6.3 Applications
The following are the applications of Microstrip antenna,
Used in Spacecraft applications
Used in Aircraft applications
Used in Low profile antenna applications.
Mobile communication
The most important requirement of the mobile application is that, the antennas should be small in size and weight. Microstrip Antennas are preferable for this application. Various types of antenna designs are made and used for marine and radar applications.
Satellite Communication
Antennas play an important role in satellite communication. Usually parabolic antennas are used in Satellite communication for transmitting information and broadcasting signals. Circular polarisation is a must in Satellite communication. A Microstrip antenna as a substitute of parabolic antenna can be used to produce polarisation by using different feeding techniques.
Application in Medical Science
Microstrip antennas which are light in weight are used in medical applications in case of emergency. Mostly annular ring and circular patch antennas are preferable for these applications.
2.7 DEFECTED GROUND STRUCTURES
The concept of defected ground structures (DGSs) is a new area of research, and its evolution originated primarily from the studies of photonic band gap (PBG) structures. The PBG structures which are used for EM applications and are referred as electromagnetic band gap (EBG) structures. They are periodic in nature, which prevent EM waves to propagate through them for a certain band of frequencies called stopband and allows to pass through a range of frequencies called passband. For microstrip structures, its ground plane is a suitable choice to implement EBG structures. But it was very difficult to use PBG based structures in microwave and millimeter frequency range because of the complexity of modelling and extraction of equivalent circuit and its parameters. In 1999, a new etched lattice was proposed by Park et al. and named it as "PBG unit structure". They simplified the geometry of PBG and used a single cell of dumbbell shaped defect etched on the ground plane to achieve stopband in C- band and X- band. Further Kim et al. used the same structure and named it as defected ground structure. Thus the DGS is regarded as the simplified variant of printed EBG structure on the ground plane.
As the name implies, the defected ground structure is the single defect or the periodic number of defects etched on the ground plane of the microstrip substrate (printed circuit board (PCB)) to achieve a feature of stopping the electromagnetic wave propagation through the substrate over a certain band of frequencies. The important property of DGS slots is its resonant behavior and this characteristic depends on the size and shape of the DGS slots. The etched DGS slot under a microstrip line disturbs the current distributions occurring in the ground plane and this disturbance changes the equivalent line parameters such as line capacitance and inductance over the defected region. DGS geometries reported in the literature include some simple shaped structures such as rectangular dumbbell head, circular dumbbell head, spiral shaped, "U" shaped and "V" shaped, dumbbell "H" shaped, cross shaped, double equilateral "U", concentric ring shaped etc. Different complex structures such as the split ring resonator (SRR), complementary split ring resonator, fractal shaped are also examined. The DGS slots are used to implement filters to suppress the unwanted harmonics, to improve the transition from passband to stopband, to achieve compactness in microwave circuits and other RF applications.
Some of the simple and complex DGS shapes are shown in the Fig. 2.12. Different geometrical shapes of DGS slots have been explored by different authors to improve the performance of the filter in the passband and in the stopband and to achieve compactness and ease of design.
DGS has many attractive features which include,
1. Simple structure
2. Wide stopband bandwidth with high suppression level than the conventional structure
3. Low insertion loss
4. Lowpass filters can be realized and implemented using smaller element values

Fig. 2.12 Different geometries of DGS used in the literature: (a) dumbbell shaped (b) spiral shaped (c) H shaped dumbbell (d) U shaped (e) dumbbell arrow head (f) concentric ring (g) split ring resonators (h) interdigital structures (i) cross shaped structures (j) dumbbell circular head (k) square head with U-slot (l) dumbbell-open loop (m) fractal shaped (n) half circle dumbbell (o) V shaped (p) L shaped (q) meander (r) U shaped head dumbbell (s) double equilateral U-shaped (t) square head slot with narrow slot gap
2.8 LITERATURE REVIEW
A number of research papers published in the microstrip antenna area have been considered.
Deepender Dabas et al. [1] proposed the circular antenna used to aperture coupled feed line and it is used as feeding to the circular tract antenna. The aperture coupling is closed all the sides of the cavity and overlapped the surface to wave intercommunication in an array environment. The active devices are used to revamp the heat dissipation. With the help of the heat dissipation, the active devices are materialized with pedestal layout. The proposed antenna has impedance bandwidth 9.3% ( 9.55 to 10.48 GHz).
Asem Al-zoubi et al. [2] proposed the circular microstrip patch antenna with a coupled spherical ring placed on the substrate. The circular microstrip antenna has the monopoly like omnidirectional radiation pattern. The proposed antenna has wider bandwidth analogous radiation pattern compared to the center fed circular patch antenna. The proposed antenna is easy to fabricate and design. It has the resonant frequency of 5.8 GHz, large impedance bandwidth and gain are 12.8 % and 5.7 dBi. The simulated and measured return loss and radiation pattern of the circular patch antenna are tested through Anechoic chamber. It is used in the satellite communication systems and radar systems. The center fed circular patch antenna is used in the dual band and broad band applications.
Mohammad Sigit Arifianto et al. [3] proposed the circular patch antenna with split ring resonators which is used for the dual-band acknowledgement of a single-band. The split ring resonators (SRR) have metamaterials structure. The proposed antenna is used for 2.4GHz WLAN and 3.3GHz WiMAX applications. The circular patch antenna is given to the microstrip feed line technique and fabricated through the FR4 epoxy material with a dielectric constant 4.4 and height of the substrate is 1.6mm. The length and width of the proposed antenna is 55mm x 40mm. To validate the dual- band capability of the proposed circular patch antenna, correlated with a conventional circular patch antenna and it resonates only at 2.4GHz .The conventional microstrip patch antenna is also fabricated on an identical dielectric substrate with the equal physical limitations. These two humane antennas are set side by side each other in provisons of reflection coefficient, VSWR (Voltage Standing Wave Ratio), gain, and radiation pattern. From the simulated results, it is manufactured by the SRR metamaterials.
Noor Mohammed Awad et al.[4] discussed the circular microstrip patch antenna with Zeroth order resonant (ZOR) mode and TM02 is used for the dual band applications. The circularly periodic mushroom structure is used for the circular patch antenna. The center fed circularly polarized antenna has the horizontal magnetic loop currents on the patch surface and low profile of 0.02? at the lower frequency band. The radiation pattern of the proposed antenna has been deliberated. The proposed antenna is fabricated with the double layered printed circuit board. The input impedance of the feed line of proposed antenna has 50? by an SMA connector. The simulated and measured results of the proposed antenna are similar, the radiation characteristics of the center fed circular patch antenna are omnidirectional with two working frequency bands. The impedance bandwidth and gain of the proposed antenna is 0.75% and 5.1 dBi for the lower frequency band, 5.8 to 8 dBi for the high frequency bands.
Xi-Wang dai et al. [5] designed a circular patch antenna by a microstrip transmission line and the boundary conditions are enforced on a portion of the microstrip feed line and surface of the patch antenna. The circular patch antenna is easy to design and fabricate. The surface currents on the patch antenna and Galerkin method of moments in the Fourier transform territory are used for the feeding. The simulated and measured results are similar. The theoretical calculations are applied to the two common feeding preparations. The direct edge feeding and proximity coupling activity is used in the Galerkin technique.
Marat Davidivitz et al.[6] proposed the circular microstrip antenna cut with circular and rectangular slot for the multiband applications. The circular patch with circular slot degenerates TM11 and TM21 modes in the orthogonal modes to the multi-band aspects. The rectangular slot on the circular patch is used for optimizing the input impedance at degenerated resonant modes and the optimum bandwidth of 1% to 2% in 1000 MHz frequency range. The circular microstrip antenna cut with circular and rectangular slot is used for the satellite and radar communication systems.
Xin hu et al. [7] designed the microstrip antenna with half ring texture and half circular plot component is used for the dual frequency bands. The half-ring is narrower than the traditional ring antenna, and the half ring texture is used for varying the resonant frequency of the antenna. The simulation and measurement results of the proposed antenna is similar. The proposed antenna works at 0.9 and 1.8 GHz. The half ring texture and half circular plot is used in satellite communication systems and radar applications.
Yishan liang et al. [8] simulated the circular patch antennas that has wide band, high gain, low cross polarization with monopole like radiation characteristics used for the wireless communication systems. The impedance bandwidth of the circular patch antenna (|S11|< -10 dB) of 36.5% (4.25-6.15 GHz) is measured at the central frequency of 5.20 GHz. The peak gains of the simulated and measured 9.7 dBi and 9.1 dBi, respectively. The simulated and measured results has the good agreement and is achieved.
Shut liu et al. [9] presented the circular patch with slots . The arc shaped slot and rectangular U shaped slot is presented on the circular patch to improve the impedance bandwidth and radiation mechanism of the proposed antenna. The circular patch which has 14% impedance bandwidth is obtained without applying the arc shaped slots and rectangular U shaped slots and 23% by applying the slots. The simulation and measured results are similar with the U-shaped slot configuration.
Nasimuddin et al. [10] proposed the effective study of rectangular and circular shape microstrip patch antennas are used for the X band. The resonant frequency is for the circular patch at 10 GHz which can be used for mobile applications. The Computer Simulating Technique (CST) Microwave Studio is used for the designing of the proposed antenna. The rectangular patch antenna has return loss of -30 dB and higher return loss compared to the return loss of circular patch antenna. The rectangular patch antenna has less value of VSWR 1.18 compared to the circular patch with VSWR 1.27. On the other hand, circular patch antenna offers about 8% higher bandwidth and practically 2.0dB less side lobe power than that of rectangular patch antenna.
Tahsin Ferdous Ara Nayna et al. [11] proposed the tappered shape radiation pattern antenna measures from the half-breed fashion. The microstrip antenna with circular patch has the commanding tone and the commanding tone is a monopole antenna. The TM 01 order mode has the more advanced order modes of the circular-ring patch antenna than the broadband. The radiation characteristics of the E-plane pattern due to the monopole higher order modes and the other order modes are over the third band and it is providing the good radiation consummation by using the hybrid resonant configuration. The circular patch is used for the wireless local area networks (WLAN), worldwide interoperability for microwave access (WiMAX).
K.M.Luk et al.[12] presented the circular microstrip patch antenna with edged slot for the wireless local area networks (WLAN) and Bluetooth applications. The shape of proposed antenna is circular. The operating frequency of the proposed antenna is 1.5-2.5 GHz. The proposed antenna is designed in the IE3D Zealand Software. The simulation results of proposed circular microstrip patch antenna for different slots are simulated. The Cavity Model for the mathematical calculation of the study of antenna. The proposed antenna is given a co-axial probe feeding. The return loss, radiation pattern are premediated in the proposed antenna.
SenerUysal et al. [13] designed a band shape which includes circular jewelry in specific configurations and is practically studied to the stopband traits not like preceding designs, a meta shielding is introduced behind it to suppress a leakage, this would be high quality for microwave circuit packages. A huge stopband is verified with a fixed prototypes designed for X-band. It’s utility in suppressing the mutual coupling in microstrip patch antennas is verified.
Ming-Tien et al. [14] discussed a middle-fed round microstrip patch antenna having paired annular ring is offered. This antenna has a low profile configuration with a monopole like radiation pattern in comparison to the center-fed spherical patch antenna the proposed antenna has a massive bandwidth and similar radiation pattern corresponding to agreement among the measured and simulated results and return loss and radiation patterns that is carried out.
S Ashok Kumar et al. [15] recommend a broadband slot line-to-square waveguide transition to the usage of truncated bowtie antenna. So, that it is with the miniaturize. The proposed transition a stepped impedance resonator is used inside the placement of the area wavelength phase within the transition. In order to confirm these simulation outcome lower back to-back systems for every transitions are fabricated and measured therefore results are in appropriate element with the simulation outcome.
Shi-Wei Qu et al. [16] proposed a wideband periodic antenna with bowtie dipoles fed by means of a microstrip line . A wideband transient from a microstrip line to a parallel strip line is carried out to achieve high-quality differential-fed mechanism, the measurements show that the antenna offers an impedance bandwidth and SWR much less than 2 and average strong unidirectional radiation pattern.
Abdullah J. Alazemi et al. [17] proposed an annular ring slot line with round polarized. The annular ring includes the slot radiator and hybrid patch coupler. The circularly polarized proposed antenna having the axial ratio is an important factor. The left hand polarization and right polarization of the antenna are measured. The impedance bandwidth and axial ratio bandwidth of the proposed annular ring slot antenna is almost equal and is used in the ultrahigh frequency (UHF), radio frequency identification (RFID). The fabrication of the antenna is very easy and cost is very low.
DebatoshGuha et al. [18] proposed the unconventional form is provided, via controlling the scale and the cascaded quantity of EBG cell this form appears a slow wave transmission line that can show off large section shift with wide bandwidth for antenna array applications. The same circuit is. also looked up to model the phase shift of EBG cell. Measured result shows that the antenna array achieve the 59% frequency bandwidth for 10-dB return-loss criterion and prevent-fire radiation sample with the front-to-a gain radiation more than 27dB. The proper agreement amongst measured, full Wave simulated, and calculated effects help the validity of the section-shifting version of structures are expecting the, precept beam attitude of the antenna array, in comparison to the conventional strong-state agreement and reduce rate and it's far much less complicated to mix in the bowtie antenna array with huge-band and prevent-fireplaces radiation
Asem Al-Zoubi et al. [19] discussed a wideband directional antenna composed of a short bowtie patch antenna and an electric powered dipole offered through the composition, an equal magnetic dipole because of the shorted bowtie patch antenna and an electric powered dipole are excited together nearly equal radiation sample within the Electric and magnetic planes are obtained. The proposed antenna has a huge impedance bandwidth that's over 66% for SWR. less than two beginning from 2.16-4.13 GHz.
Ruei-Ying Fang et al. [20] proposed a modified bow-tie antenna which reveal capacity used in Radio Frequency identification (RFID), Industrial Scientific and Medical (ISM) programs... Triple band operation is facilitated in making use of trapezoidal truncations on each hand of the bowtie antenna. The primary appealing function of the proposed antenna is its stepped forward bandwidth for triple band operation mainly in different RFID bands. A tremendous length discount of the patch vicinity is also carried out for the proposed shape. The simulated consequence for the go back loss traits are in exact settlement measured.
Shi-Wei Qu et al. [21] has designed a symmetric antennas that provide the possibility of electric power conversion. Those antennas are included with a total common place selection problem in EBL, which is decreased by means of using a demodulation technique by linear programming (LP).
Jun Lin Zhang et al. [22] had worked with localized ground heterogeneous nano bowtie antenna, It recognize to middle component, bowtie length and filling refractive index of the environment. The tunable spectral and special properties are attributed to Plasmon dipole corresponded nano bowtie. It can be well manipulated via the scale of nano bowtie antenna. In addition to the core detail of the observer gives the primary results.
Joko Muslim et al. [23] proposed the theoretical measure of the antenna which has the optical forces generated by the excessive close to the subject resolution antenna gadget through the finite distinction time area calculations are in the side of the Maxwell pressure tensor method. The bowtie shaped nanostructure with small holes are exploiting propagation waveguide modes in addition to the localized floor plasmas. The researchers proposed that the antenna gadget helps the big optical forces.
Amit A deshmukh et al. [24] proposed rectangular patch antenna with U shaped and V shaped slots for dual band, broad band applications. The slots are cut to the patch either quarter wavelength or half wavelength and surface, current distributions for dual band frequencies of rectangular patch antennas are studied, the operating frequencies are second order orthogonal mode, the radiation patterns in two principle planes.
Hui Gu et al. [25] proposed the circularly polarized rectangular patch antenna with rectangular ring slot, four varactor diodes are placed symmetrically using co axial feeding to improve the circularly polarized from 1.92 to 2.51 GHz, Omnidirectional radiation pattern and improve the efficiency from 47 % to 61 % as operating frequency.
Karthik et al. [26] introduced the rectangular patch, circular patch and elliptical patch, which are useful for wireless power transmission.
SN Ather et al.[27] developed the rectangular microstrip antenna with parasitic patches on CPW feed. The antenna is used at wireless local area network (WLAN) and worldwide interoperability microwave access (WiMAX) applications, it has wide impedance bandwidth and measured antenna gain, radiation pattern and radiation efficiency.
Lalit Kumar et al.[28] presented a compact lowpass filter designed using hexagonal shaped resonator with symmetric open stubs. To extend the stopband bandwidth, high frequency multiple transmission zeros are generated by introducing three semi circular slots on the ground plane. However, the structural complexity is high.
A Boutejdar [29] proposed a H shaped DGS with equivalent circuit model and is drawn for defected ground structure.
Lee et al. [30] proposed a compact ultra wideband circular monopole antenna and an interdigital DGS (IDDGS) etched on ground plane. An IDDGS produces multiple resonances and show good agreement in the proposed antenna.
Divya Ashirwar [31] developed a decagon shaped monopole patch applicable for multiple band like Wi-Fi, Wi MAX band and WLAN band, introduced the valley shape to increase the impedance band, radiation efficiency.
Sudeep Baudha et al. [32] developed the circular patch with corrugated ladder shaped ground for ultra-wide band, and lower order resonances are created because of circular slot on circular patch.
K.wei [33] proposed square microstrip antenna and slotted fractional DGS on ground to reduce the losses in polarization, improve the circular polarization (CP) and cross polarization of linear polarization antennas for L band applications.
M Nasar et al. [34] proposed semi fractal with slotted conductor backed plane with coplanar wave guide (CPW) for monopole ultra-wideband, dual band and more efficient radiation efficiency.
S. Hekal et al. [35] designed H shape and semi H shape defected ground structure for high efficiency, compact size and maximum wireless power transfer . The H shaped DGS has maximum efficiency of 73 %, and transfer distance of 25 mm, using quasi lumped resonators.
F. Tahar et al. [36] designed two different DGS, employ capacitive loading between two DGS which has been used for dual band with reference of admittance, invertor. It has compact size, more efficiency, dual band resonant frequency 0.3 GHz, 0.7 GHz.
L. H. Weng et al. [37] explained the basic overview of defected ground structure, transmission characteristic DGS are introduced, equivalent circuit model of different DGS are also introduced.
Hai-Wen Liu et al. [38] proposed microstrip line with one dimensional DGS, square defects are etched on ground and their non uniform amplitudes are varied. It can be used in microwave integrated circuits, monoloithic integrated circuits.
J. Wang et al. [39] proposed T shaped DGS and U shaped DGS with miniatured dual band band stop filter. The center frequency of the first stop band and second stop band are controlled by mutual coupling between T shaped DGS and U shaped DGS.
J.-K. Xiao et al. [40] introduced the U shaped DGS, useful for single band, dual bandand triple band. It can improve filter frequency selectivity, low loss, multiband operation and reduce the size. The U shaped DGS has wider bandwidth, implement the miniaturization.
X. Zheng et al. [41] proposed G shaped defected ground structure, it has been operated at dual band stop filter, generate two bands at 5.2 GHz, 9.9 GHz with low insertion loss, low size and more efficiency, used in WLAN and X band applications.
S. Y. Huang et al. [42] introduced the E shape DGS placed on ground plane. It can be used in tunable bandstop resonator and better tuning frequencies compared with square patch DGS, spiral ring DGS, H shaped DGS, dumbell DGS. It has small area, low insertion loss.
Z. Ma et al.[43] explained the lumped element circuit of the filter for dual band stop filter. It has operated frequencies of 1.7 GHz, 2.7 GHz, these dual bands are controlled by both stop bands.
X. Hu et al. [44] proposed complementary split ring resonator and split ring resonator for dual band rejection filter, low insertion loss, compact size. The transmission zero is located at 2.55 and 5.05 GHz with return loss of -36 dB and -40 dB.
V. K. velidi et al. [45] proposed the cross coupling and open ended stepped impedance resonators for dual band band stop filter. It has been operated at 900 MHz, 2100 MHz with bandwidth of 72%, 36%.
Dal Ahn et al. [46] proposed novel three dimensional defected ground structure and it has been used at low pass filter.
S.S.Kartikeyan et al. [47] introduced a deep stopband lowpass filter using open complementary type split ring resonator and open circuited stubs. Even though the stopband suppression level of the filter is high, the stopband bandwidth achieved is only up to 6 GHz with low roll-off rate and large physical size of the fabricated prototype.
Ashkan Abdipour et al. [48] designed the 3dB cut off frequency of the filter is improved by using modified hairpin resonator with long straight slots. To obtain compact low pass filter with good in band and out of band characteristics. But the stopband bandwidth achieved in both filters is low.The designed lowpass filter has a high figure of merit.
Piotr Kurgan et al. [49] proposed a cascade of inductively coupled fractal defected ground resonators are utilized to design a microstrip lowpass filter with high stopband suppression level.
L Song et al. [50] studied a systematic investigation of rectangular patch antenna bending effects and Cylindrical rectangular bending antennas for wearable applications.
W C Liu et al. [51] proposed the slotted patch antenna with co planar waveguide. It is used for dual band applications and at multi resonant modes with good impedance bandwidth.
B Yildirim et al. [52] introduced a rectangular loop shaped parasitic radiator. It increases the gain of microstrip antenna, impedance and radiation performance.
Danny L Torres [53] developed a dual band rectangular patch antenna with less return loss The return loss of antenna is less than -20 dB.
T Srinivasa Reddy [54] designed the Bowtie antenna with concentric circular slot for triple band applications. The bowtie antenna has high impedance bandwidth.
T Srinivasa Reddy [55] introduced circular slot DGS at ground plane to enhance impedance bandwidth and gain. A star polygon with concentric circular DGS used for WLAN/WiMAX applications. The simulated values of maximum gain 7.42dB at 3.6GHz.
T. Srinivasa Reddy et al. [56] developed the circular ring patch antenna with DGS for enhancement of wide bandwidth.The designed antenna is operated at frequencies 8.3GHz,11.8GHz and 14.5GHz.
T. Srinivasa Reddy et al. [57] analysed the U slotted rectangular patch antenna with geometric series DGS for triple band applications.The U slotted DGS antenna operated at three different frequencies of 8.3 GHz,11.8GHz and 14.3GHz.
T. Srinivasa Reddy et al. [58] simulated a coplanar concentric ring patch (CCRP) antenna for Ku band applications.The CCRP antenna has worked at frequencies 13.98GHz and 16.54GHz with gain 8.15dB,8.44dB.
T. Srinivasa Reddy et al. [59] presented the circular ring slots and arc slot in circular patch antenna for Ku band applications.
Hai W. Liu [60] developed the fractal rectangular with dumbbell DGS which can provide slow wave characteristics, high power handling capability, size reduction, better band gap characteristics.
B Mishra [61] presented a simple method to design an Ultra-wideband microstrip antenna. The UWB patch antenna is operating between 11.97GHz and 20.54GHz.The simulated peak gain is of 8.5dBi and radiation efficiency is of 88.5%.
Akhilesh Mohan [62] presented the dual bandpass filter using DGS. To obtain dual-band characteristics two dual bandpass filters are used. The two bandpass filters are designed ,fabricated and measured.
P. Rakesh Kumar [63] investigated a triple-band square shaped microstrip antenna.It consists of dual polygonal slits cut on top and asymmetric dual H shaped DGS etched on the bottom area of the ground plane.The simulated gains of 3.17,5.0 and 2.2dBi.
K. George Thomos [64] proposed a novel printed triple band antenna for WLAN/WiMAX applications.By adding the parasitic element the end cutoff frequency of an antenna is reduced from 6.89GHz to 6.0GHz and a notched band at 3.84 to 5.02 GHz is obtained.
A Boutejdar [65] proposed design of compact stopband extended microstrip lowpass filter by employing mutual coupled square shaped DGS and drawn equivalent circuit model for defected ground structure.
Chandrakanta kumar [66] demonstrated DGS integrated microstrip array to achieve improved polarization. A 2x 2 integrated array simulated in X-band , which has low insertion loss and used in mobile communication systems.
Sudeep Baudha Vishal Asnani [67] developed the microstrip patch antenna with I shaped patch, partial ground plane for bandwidth enhancement and triple band applications.
Vishal Asnani et al. [68] designed the curved slot on rectangular patch with partial ground plane to enhance the bandwidth, useful for 2.4/5.2/5.8 GHz, 2.5/3.5/5.5 GHz and improve the gain of proposed antenna.
Sudeep Baudha [69] presented a Miniaturized dual broadband printed slot antenna with parasitic slot and patch. The designed antenna is miniaturized to 60%. The partial slot on ground plane for dual band , minimize the antenna size and stable radiation pattern.
Dinesh Kumar V [70] simulated the U shaped DGS which creates the higher order resonances, improves the radiation efficiency of 87 % and higher gain of 5.2 dB.
Sudeep Baudha et al. [71] designed the dumbbell shaped microstrip antenna with partial ground plane used in space and satellite communications, which improve the surface efficiency.
Sudeep Baudha [72] proposed the circular patch with defected ground plane for multiple band which has stable omnidirectional, bi directional radiation pattern over ultra-wide band applications.
Kumar V. Dinesh et al.[73] explained the rectangular antenna with symmetrical placed circles in ground plane for dual band applications.
Fu Wei Wang [74] proposed the dual band antennas which are more popular and co directional DGS reduce the coupling on radiation characteristics, used for dual band MIMO applications.
X Jin [75] developed the pair of microstrip feed line with meander multimode DGS which has improved the bandwidth, efficient electric field distributions on slotted meander line and operate at dual band bandpass filter.
L Ren [76] simulated the dual band antennas that have inter digital DGS etching on ground, operate at 2.44 GHz, 3.28 GHz, stop band attenuation of greater than 30 dB.
Sandeep Kr. Singh [77] designed dual band gap coupled MSA using L slot DGS for WiMAX and WLAN applications.The designed antenna has impedance bandwidth from 3.4 to 3.7GHz and 5.725 to 5.825GHz.
Shanshan [78] reported on E shape DGS that has fractional bandwidth of 5.8 %, insertion loss of 3.6 dB for dual band substrate integrated waveguide (SIW).
Ali Arif [79] explained the DGS which has slotted ground, to improve impedance bandwidth, compactness, conformability, used for wireless body area network (WBAN), industrial, scientific and medical [ISM] band.
Shihua Cao [80] proposed a novel asymmetrical pi shaped DGS with Koch fractal curve to design lowpass filter. The pi shaped fractal DGS on ground has low insertion loss from 0Hz to 1.9GHz.
P.Kurgan [81] presented the fractal DGS that has been utilized in microstrip lowpass filter [LPF]. Lowpass filters are vital components in microwave and wireless communication devices.
Suleyman [82] explained high attenuation level in stop band, wireless for multiband geostationary satellite communications.
Kamaraiah Ismail [83] designed and fabricated Sierpinski Gasket fractal with DGS. The proposed antenna simulated using Computer Simulation Technology (CST) software and fabricated on FR4. It is used in RFID applications.
Hai W. Liu [84] proposed a novel fractal DGS for the microstrip line. The fractal defected ground structure is applied effectively to design a LPF. DGS has improved the radiation efficiency.
B. T. P Madhav et al. [85] analyzed the radiation pattern of multiband planar antenna placed on the top of a car and employed at multiband vehicular communications, mobile satellite and GSM applications.
Pravin Ratilal [86] presented the Size reduction, enhancement of impedance bandwidth by circular patch with fractal DGS slotted.
Kaijun Song [87] presented the equivalent circuit of duplexer to design and analyze the duplexer.The novel DGS resonator with Hilbert fractal structure used to reduce the circuit size.
Sarthak Singhal [88] developed the octagonal fractal antenna with feed CPW that has stable radiation patterns, operate in wide band.
S. Verma [89] proposed the Square shape fractal etched on ground which resonate at bandpass filter.
Kun Wei [90] proposed the circularly polarized antennas that have dual polarizations,the left-handed circularly polarized antenna for transmitting and right-handed circularly polarized antenna for receiving.
Ramesh Garg et al.[91] explained about various types of antennas and antenna arrays.Antenna types include rectangular,circular and triangular patches.
J S Row [92] presented the design of aperture-coupled annular-ring microstrip antennas for circular polarization.A series microstrip-line-feed is used for the CP radiation of the annular-ring microstrip antenna.
C C Wang et al. [93] discussed about circularly- polarized (CP) slot antennas. Based on the CP developed frequency reconfigurable antenna and polarization reconfigurable antenna.These two antennas are realized by using PIN diodes.
J. L. Zhang et al. [94] proposed an integrated compact circular polarization annular ring slot antenna for RFID reader.The hybrid patch coupler is integrated with the annular ring slot antenna to produce the cicular polarization.
B. Stockbroeckx et al. [95] discussed the Copolar and cross-polar radiation of vivaldi antenna on dielectric substrate.The electric field distribution and radiated fields are calculated by using Green’s functions.
Ahn D et al.[96] proposed a design of the low- pass filter using the microstrip defected ground structure. The stopband bandwidth of the lowpass filter is improved by using a multilayer structure with open stubs and DGS.
C. S. Kim et al.[97] proposed a one-dimensional periodic defected ground structure to improve the effective inducatance.The cutoff frequency characteristics are controlled by effective inducatance.The designed periodic DGS presents the good cutoff and stopband characteristics.
Liu H et al.[98] proposed a meander microstrip line with DGS.The designed configuration gives the broad stopband and improved slow-wave characteristics.
Mandal et al. [99] proposed a new compact DGS for microstrip line.The proposed DGS antenna is used to design a compact lowpass filter.
J.-S. Lim et al. [100] explained defected ground structures (DGSs), which are realized by etching a few defects on the ground plane, have been a subject of increasing interest in analyzing the microstrip line characteristics, size, shape and orientation of the slot have significant influence on the performance of the low pass filter.
Karmakar et al. [101] proposed the dumbbell shaped defect is placed under the microstrip line and Studied on the analysis of the structure have generally used the current density approaches to model the structure.
Easter B [102] developed the Equivalent Circuit of Microstrip Discontinuities. After the physical modelling of the structure, the discontinuities are modelled in the form of the basic circuit components using the previous discontinuity studies.
R. Garg et al. [103] examined discontinuities of microstrip antennas. Discontinuities changes electric and magnetic fields distributions.
Thomson et al. [104] explained calculation of Microstrip Discontinuity Inductances.Galerkin method used to calculate inductive components of microstrip discontinuity equivalent circuits.
Hamad et al. [105] studied the Controlled capacitance and inductance behaviour of L-shaped defected ground structure for coplanar waveguide
J.-S. Lim et al. [106] investigated a spiral-shaped DGS for coplanar waveguide (DGSCPW). It can be used as a kind of periodic structure.
X L Liang [107] developed the current status and future trends of UWB antenna. The Federal Communication Council (FCC) released the Ultra-Wide Band technology in 2002 range about 3.1GHzs -10.6GHzs. This technology has more attraction in modern radar and wireless communication systems.
A Subbarao et al. [108] proposed several UWB antennas which are compact in size, wide bandwidth, omnidirectional radiation pattern, stable radiation pattern and easy to fabricate. The UWB antennas are considered as important technology in wireless world.
2.9 Summary :
This chapter presented the frequency bands of EM spectrum and their applications. This gives information about the literature survey and covers the introduction about the microstrip patch antenna, its advantages and applications. It also describes about different antenna parameters.
CHAPTER 3
The Analysis of Rectangular Patch Antenna for X Band Applications
3.1 INTRODUCTION
This chapter presents the rectangular microstrip patch antennas (MSPA) which are widely used in the wireless satellite communication and modern radar communication systems. The X-band antennas are widely used in ISM (industrial, scientific and medical) applications. A novel rectangular patch antenna with transmission feed for X band applications is presented. The single resonant mode of rectangular patch antenna is simulated by transmission line feeding by varying the length of the patch, the resonant frequencies are changed. The rectangular patch antenna has operating frequency of 7.3 GHz with return loss -26.02 dB.
Cylindrical rectangular bending antennas for wearable applications and resonant frequency variation and radiation variations are studied [50]. The slotted patch antenna with co planar waveguide is used for dual band applications, the two types of shaped slots are introduced to rectangular patch and use of slots at multi resonant modes with good impedance bandwidth. The upper bandwidth for ultra wide band and lower bandwidth for WLAN applications, the band has monopole like radiation pattern for satellite applications [51].
The 4x4 rectangular patch has better gain compared to 2 x2 circular patch. Circular patch (2 x2) operates at 5.8 GHz and occupies large space, 4 x4 rectangular patch operates at 3.5 GHz and achieved gain of 23 dB [52]. The return loss of antenna is less than -20 dB when introducing parallel slots on rectangular patch and proposed antenna has dual bands [53].
A rectangular loop shaped parasitic radiator is introduced to increase the gain of microstrip antenna and radiation performance are improved. The improved gain values are from 4.5 dB to 7.8 dB [52]. The bowtie has high impedance bandwidth [54], star polygon with concentric circular DGS for WLAN, WiMAX applications [55]. Circular ring patch antenna with DGS for wide bandwidth, triple band applications [56-59].
3.2 Flowchart of methodology :

Fig. 3.1 Flowchart to design rectangular patch antenna
3.3 Design of Rectangular microstrip antenna
The design equations for the rectangular patch antenna are

Fig. 3.2 Basic Rectangular patch antenna model
To determine length
( 3.1 )
Where
L is the length of the rectangular patch
Le is the effective length of the patch
( 3.2 )
Where
h is the height of the substrate
?e is the effective dielectric constant
( 3.3 )
( 3.4 )
C is the velocity of the light
fo is the operating frequency.
To determine width
( 3.5 )
Where
W is the width of the patch
We is the effective width of the patch
( 3.6 )
?r is the relative permittivity
( 3. 7 )
The mathematical formulas for designing ground plane,
(3. 8 )
( 3 .9 )
Where
Lg is length of the ground plane
Wg is width of the ground plane.
3.4 Design of circular microstrip antenna:
The circular microstrip patch antenna is used at single mode and multimode. The modes for the circular patch antenna can be identified by treating the patch, ground plane, and the material between the two as a circular cavity. In circular patch, modes that are supported firstly by a disk microstrip antenna and substrate height of the circular patch is less (h ? ?) are TMz whose z is considered vertical to the patch. As long as the parameters of the patch, there are two orders of freedom to control (length and width) for the normal microstrip antenna. Therefore the modes are changed by arranging a substrate to the relative values of the width and length of the patch (width-to-length ratio).
To find the electric field and modes of the circular patch antenna, cylindrical coordinates and the homogeneous wave equation are used.
?2Az(?, ?, z) + k2Az(?, ?, z) = 0 ( 3.10 )
102870060833000
Fig. 3.3. Geometry of circular microstrip antenna
The TM mode and fields are related to vector potential and their boundary conditions are,
E?(0??? ?a,0??? ?2?,z? =0)=0 ( 3.11 )
E?(0??? ?a,0??? ?2?,z? =h)=0 ( 3. 12)
H?(?? =a,0??? ?2?,0?z? ?h)=0 ( 3.13 )
The magnetic vector potential is given by the equation,
Az =BmnpJm(k???)[A2cos(m??)+B2sin(m??)]cos(kzz?) ( 3.14)
Considering model formulation, a design procedure is constructed for practical design of circular microstrip patch antenna for the dominant TMz110 mode. The procedure includes the basic information which includes the dielectric constant of the substrate (?r), the resonant frequency (fr) and the height of the substrate h. The procedure is as follows:
123380537020500
( 3.15 )
Where,
16357607175500
fr is the resonating frequency.
?r is the dielectric permittivity of the substrate.
a is the actual radius of the circular patch
h is the height of the substrate.
3.5 Design of triangular microstrip antenna


Fig. 3.4. Triangular patch antenna with field distributions
For fundamental TM10 mode
QUOTE ( 3.16 )
Where QUOTE =S + QUOTE
S is each side of triangle
Se is the effective side length of triangle
h is the height of the substrate
?e is the effective dielectric constant
c is the velocity of the light.
The mathematical analysis of rectangular patch, circular patch and triangular patch antennas are discussed in the above formulae. The operating frequency, relative permittivity, and height of the substrate are important for designing of different microstrip antennas.
The rectangular patch antenna designed at X band applications have good radiation characteristics but before designing the rectangular patch, designing the circular patch, triangular patch, square patch, rectangular ring patch antennas. The four different antennas (circular, square, triangular and rectangular ring ) have low reflection coefficient values and low voltage standing wave ratio values compared to the rectangular patch antenna. So, now rectangular patch antenna is used for for X band applications.
3.6 Simulation of Circular microstrip antenna

Fig. 3.5 Circular microstrip patch antenna
The circular microstrip antenna has been designed with FR4 epoxy material with permitivity 4.4 and dimensions of the substrate is 32x26x1.6 mm3. The radius of the antenna is 10.6 mm and dimensions of the feed line is 5.45x2 mm2. The circular patch is coated with copper material and ground is coated with perfect electric conductor.

Fig. 3.6 Return loss of circular patch antenna
The Fig. 3.6 shows the reflection coefficient of the circular patch antenna, it is operating at 7.5 GHz with reflection coefficient value of -11 dB. The circular patch has very low impedance bandwidth and which is not radiated equally in all directions.

Fig. 3.7 VSWR of circular patch antenna
The Fig. 3.7 shows voltage standing wave ratio of circular patch and which has more number of radiated signals reflected back to the input. But this proposed antenna has high VSWR values ( 5 dB at 7.50 GHz). So the proposed circular patch is not useful at practical applications because of the high VSWR values.

Fig. 3.8 Maximum peak gain of circular patch antenna
The maximum gain of the circular patch antenna is 4.26 dB shown in Fig. 3.8. The gain indicates how the maximum radiation signals are transmitted to particular direction. From the Fig. 3.7, the red color indicates the maximum radiated signals, green color indicates the moderate radiation and blue color indicates the very low radiated signals.
3.7 Simulation of Triangular microstrip antenna

Fig. 3.9 Triangular microstrip patch antenna
The equatorial triangular microstrip antenna is shown in Fig.3.9, the proposed antenna has substrate dimensions of 32x26x1.6 mm3, each side of the triangle is 13.5 mm and 50? transmission line is connected to triangular patch with dimensions 6x2 mm2.The reflection coefficient, VSWR and gain values are measured for the triangular patch antenna.

Fig. 3.10 Return loss of triangular patch antenna
The Fig.3.10 shows reflection coefficient of the triangular patch antenna, which has return loss of -16.5 dB at 6.3 GHz. The triangular patch has equal sides, which radiates equally in all directions and this antenna is used at X band applications. The triangular patch has better reflection coefficient values compared to the circular patch antenna.

Fig. 3.11 VSWR of triangular patch antenna
Voltage standing wave ratio values of triangular patch antenna are shown in Fig. 3.11. The VSWR value of triangular patch antenna is 2.5 dB at resonant frequency, which is better VSWR value compared to the circular patch antenna. The maximum gain value of triangular patch antenna is 2.10 dB shown in Fig. 3.12, but compared to the circular patch antenna which has very high gain value.

Fig. 3.12 Maximum gain of triangular patch antenna
3.8 Simulation of Rectangular microstrip antenna:

Fig. 3.13 Rectangular microstrip antenna with insert feed line
The rectangular microstrip patch antennas (MSPA) are widely used in the wireless satellite communication and modern radar communication systems. The X-band antennas are used in ISM (industrial, scientific and medical) applications.
The proposed rectangular patch antenna with transmission feed operated at 7.3 GHZ with return loss of -26.02 dB. This X band is very much useful at radio frequency identification (RFID) applications to protect the cross polarization. The rectangular patch antenna with transmission line feeding for X band applications is shown in Fig.3.13. The FR4 epoxy material used for substrate with length (L2) 32mm, width (W2) 26mm and substrate has dielectric constant of 4.4 with thickness 1.6 mm. The rectangular patch is placed on top of the substrate and coated copper material with tangent loss of 0.002. The 50 ohms input impedance is connected to rectangular patch antenna. The optimized parameter values of rectangular patch antenna are mentioned in Table 3.1.
Table 3.1 Dimensions of the proposed Rectangular patch antenna
Parameter Dimension
(mm) Parameter Dimension (mm)
L1 19 L3 3
W1 12 W3 2
L2 32 L4 6
W2 26 h 1.6

Fig. 3.14 Return loss of rectangular patch antenna
The Fig. 3.14 shows the simulated return loss of the proposed rectangular antenna at operating resonant frequency. The rectangular patch antenna has operated at 7.3 GHz resonant frequency, with resonant bandwidth of 1.1 GHz (6.9 GHz-8 GHz), return loss of -26.02 dB. The simulated results of Rectangular Patch antenna are mentioned in Table 3.2.
Table 3.2 Simulated Results of Rectangular Patch antenna
Antenna Frequency (GHz) Return loss (dB) Simulated bandwidth (GHz)
Rectangular patch antenna 7.3 -26 1.1 GHz

Fig. 3.15 Comparison of return loss between different materials used for rectangular patch antenna
The proposed rectangular patch antenna is designed to use different materials like Duroid, Glass and FR4 epoxy materials. The Duroid material has relative permittivity of 2.2, relative permeability of 1 and loss tangent value is 0.0009. The Glass material has dielectric constant of 5.5, relative permeability of 1 and loss tangent is zero. These two materials are compared with FR4 epoxy material (relative permittivity=4.4, relative permeability=1 and loss tangent =0.002) shown in Fig. 3.15. The FR4 epoxy material has return loss of -26 dB and Glass material has maximum reflection coefficient value of -10 dB, Duroid has return loss of 0 dB are mentioned in Table 3.3. The maximum return loss occurs for FR4 epoxy material. So for practical fabrication of rectangular patch, FR4 epoxy material is preferred.
Table 3.3 Return loss for different materials used in the design of rectangular patch antenna
Material Return loss
Glass -10 dB
Duroid 0dB
FR4 epoxy -26 dB

Fig. 3.16 Parametric analysis on length (L1) of rectangular patch antenna
The parametric analysis on length of the rectangular patch antenna is shown in Fig. 3.16. The length values are L1= 15 mm, 17 mm, 19mm and maximum reflection coefficient values are observed at L1=19 mm(S11= -26 dB).

Fig. 3.17 Parametric analysis on width (W1) of rectangular patch antenna
The reflection coefficient of the rectangular patch antenna depends on the width of the rectangle and is shown in Fig. 3.17. The width values are w1=10mm, 12mm, 14 mm and maximum return loss is at w1=12 mm compared to the remaining two widths.

Fig. 3.18 VSWR of rectangular patch antenna
The voltage standing wave ratio of rectangular patch antenna is shown in Fig. 3.18. The VSWR value of rectangular patch antenna is 1.5 at 7.3 GHz.
The maximum gain of rectangular patch antenna is 5.19 dB at 7.3 GHz as shown in Fig. 3.19. The red color indicates the maximum signals radiated, blue color indicates the minimum signals radiated through the proposed antenna.

Fig. 3.19 Maximum gain of rectangular patch antenna


(a) (b)

(c) (d)

(e) (f)
Fig. 3.20. The radiation characteristics of rectangular patch antenna at (a) E plane 6.8 GHz, (b) H plane 6.8 GHz (c) E plane 7.3 GHz (d) H plane 7.3 GHz (e) E plane 7.9 GHz (f) H plane 7.9 GHz
The radiation characteristics of rectangular patch antenna radiated at 6.8 GHz, 7.3 GHz, and 7.9 GHz with co polarization (solid) and cross polarization (dotted) is shown in Fig. 3.20. The bidirectional radiation pattern in E plane at 6.8 GHz, 7.3 GHz and 7.9 GHz. The Quasi Omnidirectional radiation pattern at H plane of 6.8 GHz,7.9 GHz. The cross polarization of rectangular patch antenna is minimum in H plane at 7.3 GHz, co polarization is maximum in E plane at 7.3 GHz.
(a) (b)

(c)
Fig. 3.21 Field distributions of rectangular patch antenna (a) E field (b) H field (c) J field
The Elecric field (E field), magnetic field (H field) and surface current (J field) distributions of proposed rectangular patch antenna are shown in Fig.3.21. The electric field distributions of rectangular patch antenna is maximum at feed line and minimum at edges of rectangular patch and electric field of rectangular patch antena is 1.49 V/m, magnetic field is minimum compared to the electric field of the rectangular patch antenna and maximum magnetic field is 1.35 A/m. The surface current distribution of the rectangular patch antenna is 1.45 A/m.
Upto now the discussion about the circular patch, triangular patch and rectangular patch antennas were carried out and it is observed that the rectangular patch antenna has good reflection coefficent values compared to the circular patch antenna and triangular patch antenna. Moving ahead, now the discussion about the rectangular ring and square antennas is taken up. These two antennas also offer low reflection coefficient values compared to the rectangular patch shown in Fig. 3.22.

Fig. 3.22. Comparison of return loss between rectangular ring, rectangular and square patch antennas
Table 3.4 Comparative study of different microstrip patch antennas
s. no Patches Return loss (dB) VSWR Gain (dB)
1 Circular patch -11 5 4.28
2 Triangular patch -16.5 2.5 2.10
3 Rectangular patch -26 1.5 5.19
4 Square patch -14.5 5 3.76
5 Rectangular ring patch -4 12 2.09
3.8 Conclusions
This chapter presented the rectangular patch antenna with transmission line feed for X band has operated at resonant frequency 7.3GHz and used at satellite communication systems. The proposed rectangular patch antenna has good radiation characteristics,currrent distributions and maximum gain.The cross polarized losses are reduced in proposed antenna. It also presented the comparative study of different patches.
The next chapter presents the U shaped defected ground structure (DGS) introduced on the ground plane of rectangular patch antenna for dual-band applications has been investigated and the design of rectangular antenna has slotted dumbbell shape on ground for multiple-band applications.
CHAPTER 4
The Analysis of U shaped DGS for Dual Band and Dumbbell shaped DGS for Multiple Band Applications
4.1 INTRODUCTION
This chapter presents the U shaped defected ground structure (DGS) introduced on the ground plane of rectangular patch antenna for dual-band applications that has been investigated and the design of rectangular antenna has slotted dumbbell shape on ground for multiple-band applications.
The U shaped DGS has bandwidths of 500 MHz (5.4-5.9 GHz), 300 MHz (8.7-9 GHz) at two center frequencies 5.7 GHz and 8.8 GHz. The maximum return loss of the U shaped DGS at two center frequencies are -20 dB, -15.4. dB maximum gain is 4.05 dB, 8.13 dB.
Nowadays defected ground structure (DGS) is very popular in radio communication systems and the evolution of DGS from the primarily printed circuit, photonic band gap (PBG) in electro magnetics. The photonic band gap has the artificial periodic structure, it prevents the electromagnetic wave propagating over the range of frequencies. Previously photonic band gap (PBG) was used in optical communication, microwave, and millimeter wave applications. The defected ground structure has dominant of PBG, reduce the size, improve the operating bandwidth and suppress the cross polarization of radiation pattern.
The integrated array DGS for improving the radiation properties of microstrip patch, suppress the cross polarization, improve the isolation between co-polarization radiation and cross polarization radiation [50], circular monopole antenna with inter digital DGS on ground plane for wide bandwidth, multiple bands stops, which are 5.3-5.9 GHz, 2.1-3.8GHz, 7.65-7.9 GHz [51], fractal rectangular with dumbbell DGS can provide slow wave characteristics, high power handling capability, size reduction, better band gap characteristics [60]. The researchers proposed several different shapes of DGS such as compact DGS provide Ku/K band applications, dual polygonal slit square patch with H shaped DGS for IMAT2000, WiMAX, triple band operation, the dumbbell DGS for multi-band operation, wide stop bands used in many microwave and millimeter applications, the dumbbell DGS derived from equivalent circuit of equivalent inductance and capacitance [61-64]. The circular patch with rectangular DGS for the triple band, wide impedance bandwidth, good radiation characteristics of WLAN/WiMAX applications [54]. The concentric circular slots with bowtie, polygon patch operated in triple band, WLAN and WiMAX [55-56]. Geometric DGS with circular patch, U shaped slots for Ku band, wide bandwidth and operated in triple band [57-59].
The researchers have designed different DGS like E shape, C shape, dumbbell shape, rectangular co directional split ring resonator (RCSRR), meander DGS, interdigital DGS are slotted on ground for dual band applications [74-78]. The dual band antennas are more popular and co directional DGS reduce the coupling on radiation characteristics, used for dual band MIMO applications [74]. The pair of microstrip feed line with meander multimode DGS has improved the bandwidth, efficient electric field distributions on slotted meander line and operate at dual band bandpass filter [75]. The dual band antennas have inter digital DGS etching on ground, operate at 2.44 GHz, 3.28 GHz, stop band attenuation of greater than 30 dB [76], L shape DGS using for WiMAX, WLAN applications [77]. In [78] reported on E shape DGS having fractional bandwidth of 5.8 %, insertion loss of 3.6 dB for dual band substrate integrated waveguide (SIW).
The DGS which has slotted ground, to improve impedance bandwidth, compactness, conformability, used for wireless body area network (WBAN), industrial, scientific and medical [ISM] band [79]. Asymmetric pi shaped fractal DGS on ground has low insertion loss [80]. The fractal DGS has been utilized in microstrip low ass filter [LPF], high attenuation level in stop band, wireless for multiband geostationary satellite communications[81-82] and Sierpinski Gasket fractal exploits in RFID applications [83]. DGS has improved the radiation efficiency [84], employed at multiband vehicular communications, mobile satellite, GSM applications [85]. Size reduction, enhancement of impedance bandwidth by circular patch with fractal DGS slotted [86] and Hilbert fractal DGS [87]. Octagonal fractal antenna with feed CPW has stable radiation patterns, operates in wide band [88]. Square shape fractal etched on ground which resonate at bandpass filter [89], improve the circular polarization, improve forward efficiency, and forward realize gain [90-95].
A defect on the ground can change the propagation properties of a transmission line with change in the current distribution on the ground side, and the alignment of the fields between the ground and the line. The novel microwave components like couplers, dividers, filters, impedance transformers can be made up. The structure in the most basic form consists of a line with defects on its ground.
The DGS studies conducted up to now have basically focused on the dumb-bell-shaped DGS which is basically proper for high frequency filtering applications [96-100]. The dumb- bell shaped defect is placed under the microstrip line and studies on the analysis of the structure have generally used the current density approaches [101] to model the structure. The current density distribution is determined not only by the line path, but also with the discontinuities on the ground; and the resulting current distribution is interpreted as a physical model [101]. After the physical modelling of the structure, the discontinuities are modelled in the form of the basic circuit components using the previous discontinuity studies [102-104]. These discontinuity studies, beyond their old age, are still valid, and efficiently used.
Another application of the DGS is the photonic band-gap structures (PBG). The promising effect of the band gap structures in microwave devices has generated the term electromagnetic band-gap (EBG) structure. These EBG structures are formed by the periodically distributed non uniformities on the ground, substrate, or the line of a microwave component. These non-uniformities may be natural or synthetic. A periodically placed defect on the ground is a synthetic example of the kind the dumb-bell shaped [94-98], periodically placed [97], L-shaped [105], and spiral-shaped [106] DGSs are investigated and implemented. The most basic form of all these structures is a rectangular shaped DGS, and this structure is implemented in this study.
The studies in the literature covered up to now are all of filter type or resonant type structures. However, non-resonant type applications of the DGS also exist. Rectangular- shaped defected ground structure (RS-DGS) resembles a transmission line due to its physical structure. In this aspect, it can be claimed that a RS-DGS can be modelled as a transmission line of characteristic impedance Zch not equal to the characteristic impedance of the line with the same line width. This might be helpful if need to increase the impedance to the levels where line widths cannot be realized easily.
In view of the above facts, intensive investigations have been carried out on H shaped patch antenna to obtain dual bands and used at UWB applications. In the proposal, the dual bands are obtained by iteration 0, iteration 1, iteration 2 that accommodate the dimensions of the patch. The 10 dB return loss bandwidth percentage of simulated T shape DGS are 75 % (2.8-6.7 GHz), 2.94 % (10.1-10.4 GHz). The gain of dual band antennas are between 3 to 8 dB, the T shape DGS has improved the 10 dB return loss bandwidth, radiation characteristics and maximum gain.
In view of the above facts, intensive investigations have been carried out on FDGS antenna to obtain dual bands and used for UWB applications. In the proposed antenna, the dual bands are obtained by iteration 0, iteration 1, iteration 2 accommodate the dimensions of slotted fractal DGS in ground. The dual band microstrip antenna with iteration 2 FDGS is fabricated and measured. The 10 dB return loss bandwidth percentage of simulated FDGS are 5.26 % (7.4-7.8 GHz), 8.94 % (11.6-12.7 GHz) The gain of dual band antennas are between 3 to 6 dB, the FDGS has improved the 10 dB return loss bandwidth, radiation characteristics and maximum gain.
A monopole microstrip rectangular patch with dumbbell shape slotted on ground for multiple band, enhance the bandwidth. The proposed antenna is fabricated on FR 4 epoxy material with electrical permittivity of 4.4 and magnetic permeability 1. The dimensions of proposed antenna are 70 x 50 x 1.6 mm3 and the dumbbell shape is slotted on ground of substrate which resonates at four different frequencies 5.9 GHz, 7 GHz, 8.7 GHz and 9.7 GHz. The proposed antenna has bandwidths of 200 MHz, 300 MHz, 300 MHz, 300 MHz at four resonant frequencies The proposed antenna covers 4/8 GHz C band, 8/12 GHz X band and is used in radar, satellite communications. The reflection coefficient (S11), radiation characteristics, peak gain and VSWR of designed antenna are described.
The printed monopole antennas have wide growth in wireless technology and these have high gain, high efficiency, broad impedance bandwidth and planar. The defected ground structure has exponential growth with capacitive, inductive attention and the researchers are interested to develop DGS because of their compact size, easy to design two dimensional and three dimensional structure, easy to fabricate and broad bandwidth.
A H shaped DGS, coupled DGS for wide rejection of LPF, low insertion loss and mobile communication systems and equivalent circuit model is drawn for defected ground structure [65-66]. The microstrip patch has I shaped patch, partial ground plane for bandwidth enhancement, triple band applications [67], curved slot on rectangular patch with partial ground plane to enhance the bandwidth, useful for 2.4/5.2/5.8 GHz, 2.5/3.5/5.5 GHz and improve the gain of proposed antenna [68], partial slot on ground plane for dual band , minimize the antenna size, stable radiation pattern [69]. Rectangular parasitic to enhance broad and U shaped DGS creates the higher order resonances, improve the radiation efficiency of 87 % and higher gain of 5.2 dB[69-70], dumbbell shaped microstrip with partial ground plane used in space and satellite communications, improves the surface efficiency [71]. The circular patch with defected ground plane for multiple band has stable omnidirectional, bi directional radiation pattern over ultra-wide band applications [72], rectangular antenna with symmetrical placed circles in ground plane for dual band applications [73]. The researchers developed rectangular, circular shape patch with different kinds of slotted ground and useful for satellite over wireless communications and high gain, stable radiation patterns [54-58].
4.2 The analysis of circular ring Patch antenna with ladder shaped DGS:
The rectangular patch antenna with different substrate materials, various types of patches and comparison of patches were discussed in Chapter 3. But this chapter is extension of rectangular patch antenna and etching slots on ground plane. Now a days defected ground structure is used in various applications like Wireless Local Area Network (WLAN), Wi Fi, Wi Max applications, reduce the size of overall antenna. The U shaped defected ground structure is used for dual band applications and before designing the U shaped DGS, first designed the I shaped DGS and then T shaped DGS.
4.2.1 circular patch antenna with ladder defected ground structure
The circular patch antenna with ladder shaped DGS is shown in Fig.4.1.

(a) (b)
Fig. 4.1 circular patch antenna with ladder DGS
The proposed antenna is designed with FR4 epoxy material (dielectric constant=4.4) and. The reflection coefficient (S11), VSWR, radiation pattern and gain values are measured for ladder DGS.

Fig. 4.2 Return loss values of circular patch antenna with ladder DGS
The reflection coefficient (S11) of circular patch antenna with ladder DGS is shown in Fig. 4.2, frequency range from 8 GHz to 10 GHz and return loss value is -14.1 dB at 8.2 GHz. The bandwidth of antenna is 2 GHz (10 GHz-8 GHz), impedance bandwidth is 1.3%. The voltage standing wave ratio values are more than 2 for proposed antenna, VSWR value is 2.75 dB at 8.2 GHz as shown in Fig. 4.3.

Fig. 4.3 VSWR of circular patch antenna with ladder DGS etching on ground plane

(a) (b)
Fig. 4.4 Radiation chacteristics of circular patch antenna with ladder DGS slot (a) E plane (b) H plane
The radiation pattern of proposed rectangular patch antenna in E plane (XOZ plane), H plane (YOZ plane) at Phi= 0 degrees, phi=90 degrees are measured and are shown in Fig. 4.4. The co polarization and cross polarization of each E plane and H plane are measured, solid lines (black) indicates cross polarization and solid line (red) indicates co polarization. The co polarization of E plane is very low and the cross polarization is very high measured at 8.2 GHz. The cross polarization of H plane has shape of bi directional and which has very high values compared to co polarization. The peak gain value of proposed rectangular patch antenna with single slot has 4.96 dB as shown in Fig. 4.5.

Fig. 4.5 Peak gain value of circular patch antenna with ladder DGS etching on ground plane
The circular patch antenna with ladder shaped defected ground structure has very low reflection coefficient values, low bandwidth, very low impedance bandwidth and this antenna also has high VSWR value. The designed antenna has not radiated equally in all directions, very high cross polarization values and very low peak gain value at resonant frequency 8.2 GHz are also observed. So to improve these results, the circular ring with ladder defected ground structure has proposed.
4.2.2 Circular ring patch antenna with Ladder shaped DGS

Fig. 4.6 Circular ring patch antenna with ladder shaped slot etching on ground plane
The circular ring patch antenna with ladder shaped defected ground structure is shown in Fig. 4.6. The designing material of substrate and dimensions of patch is same as the previous circular patch antenna with ladder shaped defected ground structure. The introduction of circular ring with the ladder shaped DGS on ground plane leads to radiation equally in all directions compared to circular patch antenna.

Fig. 4.7 Return loss of circular ring patch antenna with ladder shaped slot on ground plane
The ladder shaped DGS has return loss of -19.25 dB at 5.2 GHz, bandwidth of 1 GHz (5-6 GHz) and very low impedance bandwidth. VSWR value of proposed RPA with ladder shaped slot has 4 at resonant frequency 8 GHz shown in Fig. 4.8.

Fig. 4.8 VSWR of circular patch antenna with ladder shaped slot on ground plane
The radiation pattern of ladder shaped DGS measured at resonant frequency of 5.2 GHz, co polarization and cross polarization of E plane, H plane are measured. The cross polarization of E plane has bi directional orientation, co polarization of E plane has quasi omnidirectional orientation and radiated in XOZ plane. The H plane has low peak gain values at both co polarization and cross polarization. The radiation characteristics are better compared to the I shaped defected ground structure.

(a) (b)
Fig. 4.9 Radiation pattern of circular ring patch antenna with T shaped DGS (a) E plane (b) H plane

Fig. 4.10 Peak gain of circular ring patch antenna with ladder shaped slot on ground plane
The maximum gain of the ladder shaped DGS has 4.94 dB, and better gain values compared to the circular shaped patch. The circular ring shaped patch has low bandwidth, low impedance bandwidth but better radiation characteristics compared to circular shaped patch and better gain values. So to improve the bandwidth, impedance bandwidth, dual band operation and better radiation characteristics, the annuar ring circular shape is introduced.
4.2.3 Design of circular ring antenna with corrugated ladder defected ground structure for dual band applications
a novel ladder defected ground structure (LDGS) has been proposed to work at dual-band applications. The dual bands are obtained by accommodating the dimensions of slotted ladder DGS in ground. The 10 dB return loss bandwidth percentage of simulated LDGS are 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz) The gain of dual band antennas are between 6 to 8 dB, the LDGS has improved the 10 dB return loss bandwidth, radiation characteristics and max gain. The fabricated antenna is tested experimentally by cross verifying the simulated results. The measurements have been carried out using vector network analyzer in anechoic chamber.
The dual band antennas are used in wireless, wide bandwidth, electromagnetic compatibility (EMC) systems etc. The dual band antennas have special features like low power consumption, less complexity, wider scan angle capabilities, less weight, low cost and easy of system integration.
The researchers design different DGS like E shape, C shape, dumbbell shape, rectangular co directional split ring resonator (RCSRR), meander DGS, interdigital DGS are slotted on ground for dual band applications [1-5]. The dual band antennas are more popular and co directional DGS reduce the coupling on radiation characteristics, used for dual band MIMO applications [1]. The pair of microstrip feed line with meander multimode DGS has improved the bandwidth, efficient electric field distributions on slotted meander line and operate at dual band bandpass filter [2]. The dual band antennas have inter digital DGS etching on ground, operate at 2.44 GHz, 3.28 GHz, stop band attenuation of greater than 30 dB [3], L shape DGS using for WiMAX, WLAN applications [4]. In [5] reported on E shape DGS has fractional bandwidth of 5.8 %, insertion loss of 3.6 dB for dual band substrate integrated waveguide (SIW).
K.wei proposed square microstrip antenna and slotted fractional DGS on ground to reduce the losses in polarization, improve the circular polarization (CP) and cross polarization of linear polarization antennas for L band applications [6]. The DGS has slotted on ground then improve wide impedance bandwidth, compact size, conformability, used for wireless body area network (WBAN), industrial, scientific, medical [ISM] band [7], asymmetric pi shaped ladder DGS on ground has low insertion loss [8]. The ladder DGS has been utilized in microstrip low pass filter [LPF], high attenuation level in stop band, wireless for multiband, geostationary satellite communications[9-10] and sierpinski gasket fractal exploits in RFID applications [11]. DGS has improved the radiation efficiency [12], employ at multi band vehicular communications, mobile satellite, GSM applications [13]. Naser proposed semi fractal with slotted conductor backed plane with coplanar wave guide (CPW) for monopole ultra-wideband, dual band and more efficient radiation efficiency [14]. Size reduction, enhancement of impedance bandwidth by circular patch with ladder DGS slotted [15], Hilbert ladder DGS [16]. Octagonal fractal antenna with feed CPW has stable radiation patterns, operates in wide band [17]. Square shape fractal etched on ground which resonate at bandpass filter [18], improve the circular polarization, improve forward efficiency, and forward realize gain [19-24].
In view of the above facts, intensive investigations have been carried out on LDGS antenna to obtain dual bands. In the proposal, the dual bands are obtained by design 1, design 2, design 3 accommodate the dimensions of slotted ladder DGS in ground. The dual band microstrip antenna with design 3 LDGS is fabricated and measured. The 10 dB return loss bandwidth percentage of simulated LDGS are 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz) The gain of dual band antennas are between 6 to 8 dB, the LDGS has improved the 10 dB return loss bandwidth, radiation characteristics and max gain..

(b)
Fig. 4.11 Design antenna geometry (a) top view (b) bottom view
Table 1. Design diemnsions
a b R1 R2 R3 c d e f g i j w p
15 20 7 5.5 4 5 6 1.8 1.6 2.5 4 5.5 3 4
The geometry of ladder DGS have design 1, design 2, design 3 shown in fig. 2. The design 1 is single circular patch with ladder DGS on ground fig. 2 (a), design 1 is turned to circular ring shape shown in fig. 2 (b) and circular ring shape considered as fractional unit which is turning to circular annular ring shown in fig. 2(c). The designed ladder DGS is operated at 5.4 GHz, 13.3 GHz and ladder DGS antenna has dielectric constant of 4.4, height 1.6 mm and tangent loss 0.001. The LDGS antenna has outer surface length (a) 15mm, width (b) 20mm and rectangular patch length ((w) 3mm, width (j) 5.5mm. The circular patch outer radius (R1) 7mm, inner radius (R2) 5.5 mm and annular circular patch radius 4 mm. The progress dimension of LDGS antenna has c=5 mm, d=6mm, e=1.8mm, f=1.6mm, g=2.5mm, i=4mm, p=4mm.
Parametric analysis

(b) (c)
Fig. 4.12 The proposed antenna configurations (a) iteration 0, (b) iteration 1, (c) iteration 2

Fig. 4.13 Comparison of S11 design 1, design 2 and design 3
The basic configuration of the proposed antenna with single circular patch with ladder defected ground structure antenna by the design 1 is shown in Fig. 2(a). The simulated results of design 1 shows only dual band at 8.7 GHz, 10.9 GHz and return losses at resonant frequencies are -14 dB,-11 dB, gain values are varied between 1 to 1.5 dB, unstable radiation pattern. In order to improve the performance of design 1, design 2 is designed with circular ring shape with the ladder ground are shown in Fig. 2(b). The design 2 has resonated at 6.5 GHz, 9.7 GHz with return losses -19 dB, -13 dB, further improvement is design 3 with circular ring of annular circle patch with ladder ground plane shown in Fig. 2(c). To obtain the dual-band frequency, stable bidirectional radiation pattern.
Results and discussion
The proposed dual band antenna has been analysed and optimized by using Finite-difference time-domain (FDTD) method using HFSS simulator. The construct antenna return loss (S11) with and without LDGS are presented for observation shown in fig. 4(a). The bandwidth of construct antenna without LDGS is very low, the antenna with LDGS is enlarged to 1.5 GHz, 700 MHz at determined frequencies are 5.4 GHz, 13.3 GHz. The enlarge bandwidth due to ladder shape DGS slotted and impedance matching. The return loss percentage bandwidth 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz).

(a)
Fig. 4.14. Design antenna with and with out ladder DGS (a) S11(dB)

Fig. 4.15 Parametric on S11 simulated R3 of proposed antenna

Fig. 4.16 Parametric on S11 simulated R2 of proposed antenna
The antenna act as LC resonant because of DGS placed below the substrate. The ladder DGS has suppressed the higher harmonics and undesirable surface wave due to ground current has to follow longer path which gives band stop characteristics. The ladder DGS has higher radiation efficiency compared to without ladder DGS. The Fabricated antenna is tested experimentally cross verifying the simulated results. The design antenna is fabricated based on optimized parameter values. The good acquirement between simulated antenna and fabricated antenna results. The measuring errors due to deception of fabrication process. The measured return loss bandwidth of 1.45 GHz, 697 GHz at dual bands shown in fig. 5. Parametric on S11 simulated R2 of proposed antenna shown in fig. 6.

Fig. 4.17 Field distribution of proposed antenna
The vector surface current distributions of circular annular ring patch antenna are shown in fig. 7. The metallic surface of ground coated with perfect electric conductor and the vector electric field has linearly current distributions of 9.74 A/m and maximum surface current flows at the edges of the slot. The vector magnetic field and surface current have surface current distributions of 7.07 A/m, 5.08 A/m. The number of iterations are increased in ground which reduces the compact size of rectangular patch and improves the surface current distributions.


(b)

(c) (d)
Fig. 4.18 Simulated Co-polar and Cross-polar of the proposed antenna at two frequencies (a) 5.4 GHz( E plane), (b) 5.4GHz(H plane), (c) 13.3GHz(E plane) (d) 13.3 GHz (H plane).
The far-field radiation pattern of co-polarization and cross-polarization in E-plane and H-plane for the proposed antenna is shown in Fig. 8 at two frequency ranges. The main lobe magnitude of co-polarization in E-plane at frequency 5.4 GHz is 6.78dBV/m and cross-polarization is 9.77dBV/m, in H-plane the co-polarization with -19dBA/m and cross-polarization with -5dBA/m. Similarly the other 13.3 GHz frequency with co-polar 6.35dBV/m and cross-polar 12.6dBV/m in E-plane and co-polar -0.5 dBA/m and cross-polar -13.6dBA/m in H-plane. The radiation efficiency is improved due to etching of Ladder DGS on ground plane.

(a) (b)
Fig. 4.19 Simulated max gain at (a) 7.6GHz (b) 12.3 GHz
The design antenna has max gain is varied from 6 to 8 dB and maximum gain is 7.91 dB at 6.62 GHz, 5.4 dB at 13.3 GHz shows in fig. 9. verify the measures in anristu MS2037C vector network analyser.
Conclusion
The ladder defected ground structure (LDGS) has been proposed to work for dual-band applications. The 10 dB return loss bandwidth percentage of simulated LDGS are 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz) The gain of dual band antennas are between 6 to 8 dB, the LDGS has improved the 10 dB return loss bandwidth, radiation characteristics and max gain. The maximum gain of 7.91dB is observed at 5.4 GHz frequency. By loading ladder DGS at the termination of the antenna maximum amount of the power radiates and minimum amount of current is distributed at the termination. This can minimise the cross polarization. The dual-band frequency ranges can be used in Radio determination applications.
CHAPTER 5
CONCLUSIONS AND FUTURE SCOPE
5.1 CONCLUSIONS
This thesis describes briefly the summary of the proposed defected ground structures and discussions on the distinct features of the developed defected ground structures for multi band applications .
The rectangular patch antenna with transmission line feed for X band has operated at resonant frequency 7.3 GHz and used at satellite communication systems. The rectangular patch antenna has good radiation characteristics, current distributions and maximum gain. The cross polarized losses are reduced in rectangular patch antenna. The rectangular patch antenna with U shaped defected ground structure (DGS) on the ground plane for dual-band applications has been discussed. The operating frequency of designed antenna is observed at two center frequencies such as 5.7 GHz, 8.8 GHz and the maximum gain of the designed antenna are 4.05, 8.09. The return loss at resonant frequencies are -20 dB, -15.4. dB. The radiation distributions are good and these frequencies are useful at X band applications.
The ladder defected ground structure (LDGS) has been proposed to work for dual-band applications. The 10 dB return loss bandwidth percentage of simulated LDGS are 27.77 % (4.5-6 GHz), 5.26 % (12.9-13.6 GHz) The gain of dual band antennas are between 6 to 8 dB, the LDGS has improved the 10 dB return loss bandwidth, radiation characteristics and max gain. The maximum gain of 7.91dB is observed at 5.4 GHz frequency. By loading ladder DGS at the termination of the antenna maximum amount of the power radiates and minimum amount of current is distributed at the termination. This can minimise the cross polarization. The dual-band frequency ranges can be used in Radio determination applications.
5.2 FUTURE SCOPE
In this work, only four varieties of defected ground structures are utilized to develop compact, dual band, UWB and multiband. By suitably designing defected ground structures of different shapes, the frequency response characteristics can be improved.
As mentioned in the thesis, as the thickness of the substrate decreases, the cutoff frequency of the rectangular patch also reduces and thus size miniaturization can be achieved. Similarly, as relative permittivity of the substrate increases, the cutoff frequency reduces. Thus a DGS is fabricated using low substrate thickness with high permittivity, compact, wide stopband and good selectivity can be achieved.
As the electromagnetic spectrum is valuable and very limited, the spectrum is utilized for a variety of applications. The spectrum utilization can be done more efficiently by using tunable or reconfigurable microstrip antennas. Reconfigurable planar filters are highly desirable now a days to use in modern wireless communications. Using simple resonator structures, tunable low pass filters can be designed for modern efficient use of the spectrum.
The most important characteristics of a DGS is its passband insertion loss. It should be of very low value so as to transfer maximum energy from the source to the load. To generate a DGS with very low passband insertion loss as well as wide stopband bandwidth, High Temperature Superconducting (HTS) technique can be used. But this method is very expensive to be implemented.
The proposed antenna models have been designed with FR4 epoxy material. But, this material has dielectric constant (?r) 4.4. However, the surface wave is more. So, the flexible materials are used to control the surface waves of the proposed antenna. In India, the manufacturing of the antenna models on flexible material is not available. In future, the proposed designs can be manufactured on flexible materials for enhancement of gain and efficiency.
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PUBLICATIONS
Journal Publications:
Karunaiah Bonigala and Dr. P V Sridevi, “The Analysis of Rectangular Patch Antenna for X Band Applications” International Journal of Research, ISSN 2236-6124, (2019) .
Karunaiah Bonigala and Dr. P V Sridevi, “Research of Dumbbell Shaped DGS to Enhance the Bandwidth and Multiple Band Applications” International Journal of Engineering and Advanced Technology, ISSN:2249-8958, Volume. 9, Issue 2 (2019), pp. 4584-4589.
Karunaiah Bonigala and Dr. P V Sridevi, “Design of Rectangular Antenna with Fractal Defected Ground Structure for Dual Band Applications”, Internationial Journal of Advanced Science and Technology, Vol.29.No.02 (2020) ,pp.2299-2306.
Karunaiah Bonigala and Dr. P V Sridevi, “Design of H Shape Patch with T Shape Slottted Defected Ground Structure for Dual band Applications” Journal of Interdisciplinary Cycle Research, ISSN:0022-1945 Vol.XII,Issue IV (2020), pp.856-864.
International Conference Publication
1. Karunaiah Bonigala and Dr. P V Sridevi, “The Analysis of U shaped DGS for Dual Band Applications” IEEE sponsored 3rd International Conference on Electronics Communication and Aerospace Technology (ICECA 2019) , RVS Technical Campus ,Coimbatore,Tamilnadu,India, 12-14,June 2019.

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