Sunil Thesis

INTERNATIONAL SOCIETY OF THESIS PUBLICATION

A Society of Research Publication

D E S I G N & A N A LY S I S O F M I C R O S T R I P PAT C H A N T E N N A U S I N G M E TA M AT E R I A L

S U N I L K U M A R T H A K U R A M I E ( E C ) , M E ( C C N )

W W W . I S T P . O R G . I N

C O P Y R I G H T © 2 0 1 2 I S T P I N C . A L L R I G H T S R E S E R V E D .

http://www.istp.org.in/

D E S I G N & A N A L Y S I S O F M I C R O S T R I P P A T C H A N T E N N A U S I N G M E T A M A T E R I A L

pg. 2

A B S T R A C T

This thesis work focuses mostly on design and analysis of microstrip patch antenna using metamaterial

as well as effects of slots made on patch antenna to improve the banwidth. Microstrip patch antenna are

preferred over other antennas in todays modern word scenario for their compatibility to be fit in Mobile ,

Aircraft , Satellites owing to very small sizes. Hence design and development of superior and cost effective

microstrip patch antenna has become an active research area.

We present characteristics of microstrip patch antennas on metamaterial substrates loaded with

complementary split-ring resonators (CSRRs). The proposed antenna utilizes CSRRs in the ground plane

altering the effective medium parameters of the substrate. Simulation results were verified by experimental

results. The experimental results confirm that the CSRR loaded patch antenna achieves size reduction and

keeping the bandwidth intect as well.

The radiation properties of a circular patch antenna with U-slot designed on glass epoxy FR-4 substrate

are obtained and compared with that of a normal circular patch antenna designed under identical conditions.

The modified antenna not only resonates at two different frequencies but also presents marked

Improvement in the bandwidth. The, return loss and VSWR are measured for simple circular patch antenna and

circular patch antenna with U-shaped slot. Reasonably good matching of modified antenna with the feed

network is obtained for both the resonance frequencies.

The designed antennas have been characterized using the commercially available software IE3D.

With the help of this we discuss reflection coefficient, transmission coefficient, VSWR, radiation pattern etc.

All the designs have the same dielectric constant ( ) 4.4, substrate thickness of 1.6 mm and loss tangent of

0.02.


pg. 3

C O N T E N T S

Nomenclature Page No

List of Figures 5 -6

Chapter 1 Introduction of microstrip patch antenna

and metamaterial 07

1.1 Microstrip patch antenna 07

1.1.1 Introduction 07

1.1.2 Advantage and Disadvantage 08

1.1.3 Basic principle of operation 09

1.1.4 Resonant Frequency 10

1.1.5 Feed technique 10

1.1.5 (a) Microstripline Feed 10

1.1.5 (b) Coaxial feed 11

1.1.5 (c) Aperture couple Feed 11

1.1.5 (d) Proximity couple Feed 12

1.1.6 Method of analysis 12

1.1.6 (a) Transmission line method 12

1.2 Metamaterial 15

1.2.1 Negative effective refractive index 15

1.2.2 Design strategies for NRM 16

1.2.2 (a) Thin metallic wire 16

1.2.2 (b) Swiss roll structure 17

1.2.2 (c) Split ring resonators 18

1.2.2 (d) Complementary SRR 19

1.3 Organization of the thesis 19

Chapter 2 Design and analysis of Microstrip

Patch Antenna 20

2.1 Design procedure 20

2.1.1 Summary of design parameters 21

2.1.2 Concluding remarks 23

Chapter 3 Microstrip patch antenna loaded with

Complementary SRR 24

3.1 Introduction 24

3.1.1 Proposed antenna configuration 24

3.1.2 Design and analysis of complementary


pg. 4

SRR loaded patch antenna 25


Chapter 4 Compact dual frequency wide band circular

Patch antenna with U slot 30

4.1 Introduction 30

4.1.1 Proposed antenna geometry 30

4.1.2 Design of circular patch antenna 31

4.1.3 Design of circular patch antenna

With U slot 32


Chapter 5 Conclusion and suggestion for future works 35

5.1 Concluding remarks 35

5.2 Suggestion for future works 35

References 36


pg. 5

L I S T O F F I G U R E S

Figure: 1.1 Structure of microstrip patch antenna

Figure: 1.2 Common shapes of microstrip patch antenna

Figure: 1.3 Microstrip line feed

Figure: 1.4 Probe fed rectangular microstrip patch antenna

Figure: 1.5 Aperture coupled feed

Figure: 1.6 Proximity feed

Figure: 1.7 Microstrip line

Figure: 1.8 Electric field lines

Figure: 1.9 Microstrip patch antenna

Figure: 1.10(a) Top view(patch antenna)

Figure: 1.10(b) Bottom view(patch antenna)

Figure: 1.11 Metallic wire meshes with negative dielectric permitivity

Figure: 1.12 Swiss roll structure

Figure: 1.13(a) Circular structure

Figure: 1.13(b) Square structure

Figure: 1.14 Frequency dependence of effective permittivity for a SRR

Figure: 1.15(a) Circular structure

Figure: 1.15(b) Square structure

Figure: 2.1 Simulated geometry of patch antenna

Figure: 2.2 Photograph of patch antenna(top layer)

Figure: 2.3 Photograph of patch antenna(Bottom layer)

Figure: 2.4 Current distribution

Figure: 2.5 Return loss Vs frequency of patch antenna

Figure: 2.6 VSWR v/s frequency of patch antenna

Figure: 2.7 Comparative graph of return loss Vs frequency

Figure: 3.1 Configuration of metamaterial substrate antenna

Figure: 3.2 Comparision of simulated return loss


Figure: 3.4 Unit cell CSRR


pg. 6

Figure: 3.5 (a) Simulated geometry of patch loaded with CSRR (top layer)

Figure: 3.5 (b) Simulated geometry of patch loaded with CSRR (bottom layer)

Figure: 3.6 (a) photograph of fabricated antenna (upper layer)

Figure: 3.6 (b) photograph of fabricated antenna (upper layer)

Figure: 3.7 (a) photograph of fabricated antenna (bottom layer)

Figure: 3.7 (b) photograph of fabricated antenna (bottom layer)

Figure: 3.8 Return loss Vs frequency of a normal patch antenna

Figure: 3.9 Return loss Vs frequency of a CSRR loaded patch antenna

Figure:3.10 Phase change at1.4GHz of a CSRR loaded patch antenna


Figure: 4.1 Proposed geometry of circular patch antenna with U slot

Figure: 4.2 Simple circular patch antenna

Figure: 4.3 Variation of S11 with frequency of a circular patch antenna

Figure: 4.4 Circular patch antennas with U slot made at the patch

Figure: 4.5 Photograph of U slot circular patch antenna (top layer)

Figure: 4.6 Photograph of U slot circular patch antenna (bottom layer)

Figure: 4.7 Variation of S11 with frequency of a U slot circular patch antenna


Figure: 4.9 Variation of VSWR with frequency


pg. 7

CHAPTER ONE

INTRODUCTION OF MICROSTRIP PATCH ANTENNA

& METAMATERIAL

1.1 MICROSTRIP PATCH ANTENNA

Microstrip antennas are attractive due to their light weight, conformability and low cost [7]. These antennas

can be integrated with printed strip-line feed networks and active devices. This is relatively new area of antenna

engineering. The radiation properties of micro strip structures have been known since the mid 1950‟s.[1] The application

of this type of antennas started in early 1970‟s when conformal antennas were required for missiles. Rectangular and

circular micro strip resonant patches have been used extensively in a variety of array configurations. A major contributing

factor for recent advances of microstrip antennas is the current revolution in electronic circuit miniaturization brought

about by developments in large scale integration. As conventional antennas are often bulky and costly part of an electronic

system, micro strip antennas based on photolithographic technology are seen as an engineering breakthrough.

1.1.1 INTRODUCTION

In its most fundamental form, a microstrip Patch antenna consists of a radiating patch on one side of a dielectric

substrate which has a ground plane on the other side as shown in Figure 1.1. The patch is generally made of conducting

material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually photo

etched on the dielectric substrate.

Figure: 1.1 structure of a microstrip patch antenna

In order to simplify analysis and performance prediction, the patch is generally square, rectangular, circular, triangular,

and elliptical or some other common shape as shown in Figure 2.2.For a rectangular patch, the length L of the patch is

usually 0.3333λo< L < 0.5 λo, where λo is the free-space wavelength. The patch is selected to be very thin such that t <<

λo (where t is the patch thickness). The height h of the dielectric substrate is usually 0.003 λo≤h≤0.05 λo.

Patch Dielectric of

height h

Ground plane


pg. 8

The dielectric constant of the substrate (εr) is typically in the range 2.2 ≤ εr ≤ 12. microstrip patch antennas radiate

primarily because of the fringing fields between the patch edge and the ground plane. For good antenna performance, a

thick dielectric substrate having a low dielectric constant is desirable since this provides better efficiency, larger

bandwidth and better radiation. However, such a configuration leads to a larger antenna size. In order to design a compact

microstrip patch antenna, substrates with higher dielectric constants must be used which are less efficient and result in

narrower bandwidth. Hence a trade-off must be realized between the antenna dimensions and antenna performance.

Figure: 1.2 Common shapes of microstrip patch antenna [7]

1.1.2 ADVANTAGE AND DISADVANTAGE

Microstrip patch antennas are increasing in popularity for use in wireless applications due to their low-profile

structure. Therefore they are extremely compatible for embedded antennas in handheld wireless devices such as cellular

phones, pagers etc... The telemetry and communication antennas on missiles need to be thin and conformal and are often

in the form of Microstrip patch antennas. Another area where they have been used successfully is in Satellite

communication. Some of their principal advantages are given below: [7]

• Light weight and low volume.

• Low profile planar configuration

• Low fabrication cost,

• Supports both, linear as well as circular polarization.

• Can be easily integrated with microwave integrated circuits

• Capable of dual and triple frequency operations.

• Mechanically robust when mounted on rigid surfaces.

Microstrip patch antennas suffer from more drawbacks as compared to conventional antennas. Some of their major

disadvantages discussed by Garg [9] are given below:

• Narrow bandwidth


pg. 9

• Low efficiency

• Low Gain

• Extraneous radiation from feeds and junctions

• Poor end fire radiator except tapered slot antennas

• Low power handling capacity.

• Surface wave excitation

Microstrip patch antennas have a very high antenna quality factor (Q). It represents the losses associated with the

antenna where a large Q leads to narrow bandwidth and low efficiency. Q can be reduced by increasing the thickness of

the dielectric substrate. But as the thickness increases, an increasing fraction of the total power delivered by the source

goes into a surface wave. This surface wave contribution can be counted as an unwanted power loss since it is ultimately

scattered at the dielectric bends and causes degradation of the antenna characteristics. Other problems such as lower gain

and lower power handling capacity can be overcome by using array configuration forthe elements.

1.1.3 BASIC PRINCIPLES OF OPERATION

The metallic patch essentially creates a resonant cavity, where the patch is the top of the cavity, the ground plane

is the bottom of the cavity, and the edges of the patch form the sides of the cavity. The edges of the patch act

approximately as an open-circuit boundary condition. Hence, the patch acts approximately as a cavity with perfect electric

conductor on the top and bottom surfaces ,and a perfect “magnetic conductor” on the sides. This point of view is very

useful in analyzing the patch antenna, as well as in understanding its behavior. Inside the patch cavity the electric field the

electric field is essentially z directed and independent of the z coordinate. Hence, the patch cavity modes are described by

a double index (m, n). For the (m, n) cavity mode of the rectangular patch the electric field has the form

Ez(x,y) = Amn Cos ( ) Cos ( ) -------------------------------- (i)

Where L is the patch length and W is the patch width. The patch is usually operated in the(1, 0) mode, so that L is the

resonant dimension, and the field is essentially constant in the y direction. The surface current on the bottom of the metal

patch is then x directed, and is given by For this mode the patch may be regarded as a wide microstrip line of width W,

having a resonant length L that is approximately one-half wavelength in the dielectric. The current is maximum at the

centre of the patch, x = L/2, while the electric field is maximum at the two“ radiating” edges, x = 0 and x = L. The width W

is usually chosen to be larger than the length (W =1.5 L is typical) to maximize the bandwidth, since the bandwidth is

proportional to the width. (The width should be kept less than twice the length, however, to avoid excitation of the (0,2)

mode.) At first glance, it might appear that the microstrip antenna will not be an effective radiator when the substrate is

electrically thin, since the patch current in will be effectively shorted by the close proximity to the ground plane. If the

modal amplitude A10 were constant, the strength of the radiated field would in fact be proportional to h. However, the Q

of the cavity increases as h decreases (the radiation Q is inversely proportional to h). Hence, the amplitude A10 of the

modal field at resonance is inversely proportional to h. Hence, the strength of the radiated field from a resonant patch is

essentially independent of h, if losses are ignored. The resonant input resistance will likewise be nearly independent of h.

This explains why a patch antenna can be an effective radiator even for very thin substrates, although the bandwidth will

be small.


pg. 10

1.1.4 RESONANT FREQUENCY

The resonance frequency for the (1, 0) mode is given by

fo = ------------------ ------- 1.1.4 (a)

Where c is the speed of light in vacuum. To account for the fringing of the cavity fields at the edges of the patch, the

length, the effective length Le is chosen as

Le= L + 2ΔL------------------ ------- 1.1.4 (b)

The formula for the fringing extension [6] is

--------------- 1.1.4 (c)

where

----------1.1.4(d)

1.1.5. FEED TECHNIQUES

Microstrip patch antennas can be fed by a variety of methods. These methods can be classified into two

categories:-

CONTACTING AND NON-CONTACTING.

In the contacting method, the RF power is fed directly to the radiating patch using a connecting element such as a

microstrip line. In the non-contacting scheme, electromagnetic field coupling is done to transfer power between the

microstrip line and the radiating patch. The four most popular feed techniques used are the microstrip line, coaxial probe

(both contacting schemes), aperture coupling and proximity coupling (both non-contacting schemes).

1.1.5 (a) MICROSTRIP LINE FEED

In this type of feed technique, a conducting strip is connected directly to the edge of the Microstrip patch as

shown in Figure 1.3. The conducting strip is smaller in width as compared to the patch and this kind of feed arrangement

has the advantage that the feed can be etched on the same substrate to provide a planar structure.

Figure: 1.3 Microstrip Line Feed [7]


pg. 11

The purpose of the inset cut in the patch is to match the impedance of the feed line to the patch without the need for any

additional matching element. This is achieved by properly controlling the inset position. Hence this is an easy feeding

scheme, since it provides ease of fabrication and simplicity in modeling as well as impedance matching. However as the

thickness of the dielectric substrate being used, increases, surface waves and spurious feed radiation also increases, which

hampers the bandwidth of the antenna. The feed radiation also leads to undesired cross polarized radiation.

1.1.5 (b) COAXIAL FEED

The Coaxial feed or probe feed is a very common technique used for feeding Microstrip patch antennas. As seen

from Figure 1.4, the inner conductor of the coaxial connector extends through the dielectric and is soldered to the

radiating patch, while the outer conductor is connected to the ground plane.

Figure: 1.4 Probe fed Rectangular Microstrip Patch Antenna [7]

The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the patch in

order to match with its input impedance. This feed method is easy to fabricate and has low spurious radiation. However, a

major disadvantage is that it provides arrow bandwidth and is difficult to model since a hole has to be drilled in the

substrate and the connector protrudes outside the ground plane, thus not making it completely planar for thick substrates

(h >0.02λo). Also, for thicker substrates, the increased probe length makes the input impedance more inductive, leading to

matching problems [11]. It is seen above that for a thick dielectric substrate,which provides broad bandwidth, the

microstrip line feed and the coaxial feed suffer from numerous disadvantages. The non-contacting feed techniques which

have been discussed below, solve these issues.

1.1.5 (c) APERTURE COUPLED FEED

In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane as

shown in Figure 1.5. Coupling between the patch and the feed line is made through a slot or an aperture in the ground

plane.

Figure: 1.5 Aperture coupled feed [7]


pg. 12

The coupling aperture is usually centered under the patch, leading to lower cross-polarization due to symmetry of the

configuration. The amount of coupling from the feed line to the patch is determined by the shape, size and location of the

aperture. Since the ground plane separates the patchand the feed line, spurious radiation is minimized. Generally, a high

dielectric material is used for bottom substrate and a thick, low dielectric constant material is used for the top substrate to

optimize radiation from the patch . The major disadvantage of this feed technique is that it is difficult to fabricate due to

multiple layers, which also increases the antenna thickness. This feeding scheme also provides narrow bandwidth.

1.1.5 (d) PROXIMITY COUPLING

This type of feed technique is also called as the electromagnetic coupling Scheme. As shown in figure 1.5, two

dielectric substrates are used such that the feed line is between the two substrates and the radiating patch is on top of the

upper substrate. The main advantage of this feed technique is that it eliminates spurious feed radiation and provides very

high bandwidth. Due to overall increase in the thickness of the microstrip patch antenna. This scheme also provides

choices between two different dielectric media, one for the patch and one for the feed line..

Figure: 1.6 Proximity Feed Technique [7]

1.1.6 METHODS OF ANALYSIS

The preferred models for the analysis of microstrip patch antennas are the transmission line model, cavity model,

and full wave model (which include primarily integral equations /Moment Method). The transmission line model is the

simplest of all and it gives good physical insight but it is less accurate. The cavity model is more accurate and gives good

physical insight but is complex in nature. The full wave models are extremely accurate, versatile and can treat single

elements, finite and infinite arrays, stacked elements, arbitrary shaped elements and coupling. These give less insight as

compared to the two models mentioned above and are far more complex in nature.

1.1.6 (a) TRANSMISSION LINE MODEL

This model represents the microstrip antenna by two slots of width W and height h, separated by a transmission

line of length L. [7] The microstrip is essentially a non-homogeneous line of two dielectrics, typically the substrate and

air.

Figure: 1.7 Microstrip line [7] Figure: 1.8 Electric field lines [7]


pg. 13

Hence, as seen from Figure 1.7, most of the electric field lines reside in the substrate and parts of some lines in air. As a

result, this transmission line cannot support pure transverse-electromagnetic (TEM) mode of transmission, since the phase

velocities would be different in the air and the substrate. Instead, the dominant mode of propagation would be the quasi-

TEM mode. Hence, an effective dielectric constant (εeff) must be obtained in order to account for the fringing and the

wave propagation in the line. The value of εeff is slightly less then εr because the fringing fields around the periphery of

the patch are not confined in the dielectric substrate but are also spread in the air as shown in Figure 1.7 above. The

expression for εreff is given by Balanis [7] as:

------1.1.6 (a)

where εreff = effective dielectric constant

εr = dielectric constant of substrate

h = height of dielectric substrate

W = width of the patch

Consider Figure 1.8 above, which shows a rectangular microstrip patch antenna of length L, width W resting on a

substrate of height h. The co-ordinate axis is selected such that the length is along the x direction, width is along the y

direction and the height is along the z direction.

Figure: 1.9 Microstrip patch antenna [7]

In order to operate in the fundamental TM10 mode, the length of the patch must be slightly less than λ/2 where λ is the

wavelength in the dielectric medium and is equal to λo/√εreff where λo is the free space wavelength. The TM10 mode

implies that the field varies one λ/2 cycle along the length, and there is no variation along the width of the patch. In the

Figure 1.10 (a) shown below , the microstrip patch antenna is represented by two slots, separated by a transmission line of

length L and open circuited at both the ends. Along the width of the patch, the voltage is maximum and current is

minimum due to the open ends. The fields at the edges can be resolved into normal and tangential components with

respect to the ground plane.[7]


pg. 14

Figure: 1.10(a) Top view Figure: 1.10(b) bottom view

It is seen from Figure 1.10 (b) that the normal components of the electric field at the two edges along the

width are in opposite directions and thus out of phase since the patch is λ/2 long and hence they cancel each other in the

broadside direction. The tangential components (seen in Figure 1.10 (b)) , which are in phase, means that the resulting

fields combine to give maximum radiated field normal to the surface of the structure. Hence the edges along the width can

be represented as two radiating slots, which are λ/2 apart and excited in phase and radiating in the half space above the

ground plane .The fringing fields along the width can be modeled as radiating slots and electrically the patch of the

microstrip antenna looks greater than its physical dimensions. The dimensions of the patch along its length have now been

extended on each end by a distance ΔL, which is given empirically by

---------1.1.6 (b)

where

--------1.1.6 (a)

The effective length of the patch Leff now becomes

Leff = L +2ΔL --------1.1.6 (c)

For a given resonance frequency fr , the effective length Leff is given by [4] as

--------1.1.6 (d)

For a rectangular microstrip patch antenna , the resonance frequency for any TMmn is given as


pg. 15

fo = [( )2 + ( )

2]1/2

-1.1.6 (e)

where m and n are modes along L and W respectively.

for efficient radiation , the width W is given as

--------1.1.6 (f)

Where C is the free space velocity of light

1.2 METAMATERIAL

The advent of micro system technologies and nanotechnologies enabled breakthroughs in many different areas

of science and technology, offering functionalities well beyond the natural ones. It enabled structuring of materials for

electromagnetic and optical applications in manners previously unimaginable. Among probably the best known examples

of novel electromagnetic structures are photonic crystals and the negative refractive index metamaterials, popularly

known as „left-handed‟ materials [17]. These enabled extension of the operation of passive and active elements for

microwave and optical applications beyond the limits previously deemed impossible. Another result was an extreme

miniaturization of components, sometimes even three to four orders of magnitude. Metamaterials are artificial materials

engineered to provide properties which "may not be readily available in nature".These materials usually gain their

properties from structure rather than composition, using the inclusion of small inhomogeneities to enact effective

macroscopic behavior. Negative refractive index metamaterials (NRM) are artificial composites, characterized by

subwavelength features and negative effective value of refractive index. These materials were theorically predicted in

1968 by Vaselago [4]. With the arrival of micro- and nanofabrication, new possibilities opened for practical

implementation of different metamaterials and the field became intensely studied by a number of research teams.

Extremely influential were seminal texts by Pendry . A further boost to the field came when the existence of NRM was

experimentally confirmed by Smith, Shelby [11]. The applicability of NRM for lensing which avoids the diffraction limit

by utilizing both periodic and evanescent electromagnetic waves, as proposed by Pendry in 2000 [10] even further

increased the interest for NRM. The field continued to expand owing to the fact that the Maxwell equations are scalable,

thus practically the same strategies can be used for the microwave and the optical range, including the transmission line

approach.

Today the number of the teams studying NRM and the number of published treatises on this topic are both

increasing exponentially. The aim of this paper is to present a comprehensive review of the state of the art in the rapidly

expanding field of NRM. We examine electromagnetic and physics of these materials, focusing our attention to some

issues which may appear counter-intuitive. We systematize the most important approaches to the design and application of

the NRM.

1.2.1 NEGATIVE EFFECTIVE REFRACTIVE INDEX

The complex refractive index of a given medium is defined as the ratio between the speed of an electromagnetic wave

through that medium and that in vacuum and can thus be written as n = με, where μ is complex relative magnetic


pg. 16

permeability and ε complex relative dielectric permittivity. If both ε and μ are negative in a given wavelength range, this

means that we may write μ = |μ| exp( iπ) and in an equivalent fashion ε = |ε| exp( iπ). It follows that

=

= - -------- 1.2.1 (a)

i.e. the refractive index of a medium with simultaneously negative μ and ε must be negative. Since no known material

inherently possesses negative permeability and permittivity, NRM metamaterial is a composite of two materials which

individually show ε<0 and μ<0. This raises a question when it is permissible to describe such a composite as a medium

with negative effective index.

1.2.2 DESIGN STRATEGIES FOR NRM

It is known that highly conductive metals with permittivity dominated by plasma-like behavior (as described

by Drude model) show negative dielectric permittivity in a narrow range at UV/visible frequencies. However, typical

materials with negative permeability or negative permittivity are composites consisting of a large number of the basic

building blocks described as unit cells (to retain correspondence with single crystals of natural materials). These building

blocks are also referred to as electric (ε<0) or magnetic (μ<0) „particles‟ and are often composed of dielectric with metal

inclusions. The characteristic dimensions of NRM particles have to be much smaller than the operating wavelength (in

order for the effective medium approach to be applicable), but still macroscopic, i.e. much larger than the atomic or ionic

dimension of their constituent materials.

All NRM structures fabricated until now were highly dispersive and dissipative. The main cause of dissipation is large

absorption due to conduction losses in the metal parts of the NRM. The main structures utilized to obtain NRM include

thin metallic wires, metal cylinders, „Swiss roll‟ structures, split ring and complementary split ring resonators (SRR),

omega structures, broadside-coupled or capacitivelly loaded SRRs, capacitivelly loaded strips, space-filling elements, etc.

Of these, only the most important ones will be presented here.

1.2.2 (a) THIN METALLIC WIRES

Thin metallic wires were described as one of the earliest structures with negative permittivity. The media with

embedded thin metallic wires as an artificial dielectrics for microwave applications were reported in 1953 [3].The

structure with ε < 0 described by Pendry consists of a square matrix of infinitely long parallel thin metal wires embedded

in dielectric medium

Figure: 1.11 Metallic wire mesh with negative dielectric permittivity [3]


pg. 17

In the situation shown in Fig. 1.11 the medium is vacuum or air, the unit cell length is a and the radius of a single wire is

r<<a. If plasma frequency for the longitudinal plasma mode is

---------------- 1.2.2 (i)

The effective dielectric permittivity can be written as

----------------1.2.2 (ii)

i.e. it becomes negative for ω<ωp. The approximate value at the right-hand side of the above expression is valid if

conductance ζ→∞.

1.2.2 (b) ‘SWISS ROLL’ STRUCTURES

The induced currents in a particle (both real and displacement ones) contribute to its effective magnetization through their

magnetic moments. This contribution is non-negligible if at the same time their electric polarizability is small. For

instance, if the effective permeability of the structure of metal cylinders is considered, similar to that shown in Fig. 1.12,

one obtains that its effective permeability cannot reach negative values. However, the introduction of capacitive elements

into the structure furnishes μ<0.

This can be practically done by rolling up a metal sheet into spiral coils which assume the form of a cylinder (Fig. 1.12).

This is the popularly know Swiss roll structure.[8]

Figure: 1.12 swiss roll structure[8]

The sheets in the Swiss roll coils are separated by an insulator with a thickness d. If the number of coils is N and their per

unit length resistance is ρ, the effective μ becomes

----- 1.2.2 (iii)

Swiss roll structures are especially convenient for low frequency operation.


pg. 18

1.2.2 (c) SPLIT RING RESONATORS

For decades, and starting in the early 1950s, different ring or ring-like structures with negative permeability were of

interest as building blocks for artificial chiral materials in microwave. A split ring was described in this context in the

textbook by Schelkunoff and Friis [1]. A double split ring resonator (SRR) (Fig1.13) is a highly conductive structure in

which the capacitance between the two rings balances its inductance. A time-varying magnetic field applied perpendicular

to the rings surface induces currents which, in dependence on the resonant properties of the structure, produce a magnetic

field that may either oppose or enhance the incident field, thus resulting in positive or negative effective μ. In other words,

the operation of a SRR represents an 'over-screened, under-damped' response of material to electromagnetic stimulation.

For a circular double split ring resonator (Fig. 1.13) in vacuum and with a negligible thickness the following approximate

expression is valid .

---------- 1.2.2 (iv)

Where a is unit cell length and ζ is electrical conductance.

Figure: 1.13 (a) circular structure [1] (b) square structure [1]

Dark: thin metal film

Figure: 1.14 frequency dependence of effective permittivity for a split ring resonator. Shaded area denotes negative μ

region.[1]


pg. 19

The shape of the frequency dependence of є is shown in Fig. 1.14 It can be seen that there is a narrow frequency range

where the effective permeability is below zero.

The resonant frequency (for which μeff→±∞)

Split ring resonator is probably the most often used and analyzed negative permeability building block for the NRM.

1.2.2 (d) COMPLEMENTARY SRR

Structures complementary to double split rings were designed and produced by applying the Babinet principle to the

split rings [14]. In this way structures with apertures in metal surface are obtained, as shown in Fig. 1.15 These

complementary split rings (CSRR) [14] create negative ε instead of μ in a narrow range near the resonance frequency.

Figure: 1.15 (a) circular structure (b) square structure

Dark : thin metal film

1.3 ORGANIZATION OF THE THESIS

This topic “Design & Analysis of Microstrip patch antenna Using Metamaterial” covers all the work which I have

done in this thesis.In the chapter two of this thesis The basic design of microstrip patch antenna is covered.

Chapter three of this thesis covers design and analysis of microstrip patch antenna loaded with complementary

split ring resonators which achieves size reduction as well as keeping the bandwidth intect.

In the chapter four of this thesis the design of compact dual frequency wide band circular patch antenna with U

slot is carried out and analysed. By comparision of return loss of simple circular patch antenna and circular patch antenna

with U slot, it is evident that the bandwidth is greatly enhanced and there is an scope of future works in this area.

In chapter five the concluding remarks and suggestion for further work of all the thesis is presented.


pg. 20

CHAPTER TWO

DESIGN AND ANALYSIS OF MICROSTRIP

PATCH ANTENNA

2.1 DESIGN PROCEDURE:

Based on the simplified formulation that has been described, a design procedure is outlined which leads

to practical design of rectangular microstrip patch antennas. The procedure assumes that the specified

information includes the dielectric constant of the substrate (εr), the resonant frequency (fr) , the height of the

substrate (h) and the loss tangent (δ).

SPECIFY :-

The software used to model and simulate the Microstrip patch antenna is Zeland Inc‟s IE3D. IE3D is a full-

wave electromagnetic simulator based on the method of moments. It analyzes 3D and multilayer structures of general

shapes. It has been widely used in the design of MICs, RFICs, patch antennas, wire antennas, and other RF/wireless

antennas. It can be used to calculate and plot the S11 parameters, VSWR, current distributions as well as the radiation

patterns.


Length of the patch antenna = 54.775 mm

width of the patch antenna = 70.00 mm

Resonant frequency = 1.3 GHz


pg. 21

2.1.1 SUMMARY OF DESIGN PARAMETERS

Figure: 2.2 Photograph of patch antenna (top layer)

.

Figure: 2.3 Photograph of patch antenna (bottom layer)

Frequency 1.3GHz

Length 54.775 mm

Width 70 mm

Cut width 5.009 mm

Cut depth 9.9 mm

Path length 44.9 mm

Path width 3.009 mm

Return loss -24.16 dB

VSWR 1.132


pg. 22

Figure: 2.4 current distributions

The 3D current distribution plot gives the relationship between the co-polarization (desired) and cross-polarization

(undesired) components. Moreover it gives a clear picture as to the nature of polarization of the fields propagating through

the patch antenna.

figure 2.4 clearly shows that the patch antenna is linearly larized.

Figure: 2.5 Return loss Vs freq of patch antenna

Figure: 2.6 VSWR Vs freq of patch antenna


pg. 23

Figure: 2.7 Comparative Graph of Return loss with Frequency

Return loss is measured using a spectrum analyzer. Numerical calculations of the Return loss is performed using

the method of moments (mom) based electromagnetic solver IE3D commercial software. Measured and simulated return

losses are presented in Figure 2.6(a) & 2.6(b), which exhibits a good agreement. Some minor discrepancies between the

measured and simulated return loss values can be attributed to some impedance mismatches as a result coax-to-microstrip

transitions connector side and also imperfections in fabrication process.

2.1.2 CONCLUDING REMARKS

A simple microstrip patch antenna has been designed and fabricated as shown in Figure 2.2 & 2.3. it is clear that

from figure 2.5 and fig 2.7 the return loss at the frequency of operation 1.3 GHz is more than -20 dB . subsection 2.1.1

shows the summary of design parameters. By varying the cutwidth and cutdepth and of course by using the optimization

method in IE3D simulation process, very good return loss up to -45 dB can be achieved. However this design suffers from

the difficulties of narrow bandwidth and larger size which could be alleviated by using defected ground structure and

artificially structured metamaterial in the subsequent chapter.


pg. 24

CHAPTER THREE

MICROSTRIP PATCH ANTENNA LOADED WITH COMPLEMENTARY SRR

3.1 INTRODUCTION

We present characteristics of microstrip patch antennas on metamaterial substrates loaded with complementary

split-ring resonators (CSRRs). The proposed antenna utilizes CSRRs in the ground plane altering the effective medium

parameters of the substrate. To characterize the performance of the CSRR loaded microstrip antenna, the metamaterial

substrate has been modeled as an effective medium with extracted constitutive parameters. Simulation results were

verified by experimental results. The experimental results confirm that the CSRR loaded patch antenna achieves size

reduction and maintaining the same bandwidth as well. Metamaterials [13] are finding numerous applications for novel

antennas. One such application is the use of artificial materials for compact antennas. Miniaturization of microstrip

antennas has been attempted for a long time using various different methods. Most popular and traditional way would be

to use a high permittivity substrate decreasing the guided wavelength in the substrate, so that the overall antenna size is

reduced [4]. However, this approach has a drawback resulting in the tendency for more of the energy delivered to the

antenna to be trapped in substrates with high permittivities, which eventually decreases the antenna impedance bandwidth.

To overcome the drawbacks of the patch antenna on a high permittivity substrate, several remedies have been proposed

using artificial structures in conjunction with the patch element [6], [19]. In this chapter, we propose a new design

approach to the realization of compact antennas with improved impedance bandwidth using an artificial substrate based

on complementary split ring resonators (CSRRs) and present the simulated and measured characteristics of the designed

antenna. The characteristics of split-ring resonators (SRRs) have been already studied by several groups [12], [18]. In

complementary structures, due to the fact that the electric boundary conditions on the metal are exchanged with magnetic

ones, the structure becomes effectively dual. thus, the CSRRs electromagnetic behavior is essentially an electric dipole

excited by an axial electric field exhibiting similar propagation properties as an effective negative є medium [14],[15]. We

investigate a microstrip patch antenna on a metamaterial substrate with CSRRs employed in the ground plane, and

examine the resonant frequency, impedance bandwidth, and radiation characteristics using the effective medium

approach. The comparison of the impedance bandwidth between the microstrip patch antenna on a conventional high

permittivity substrate and with the CSRR loaded metamaterial substrate is presented. The experimental results

demonstrated that a size reduction is possible for a microstrip antenna without sacrificing the bandwidth by using the

metamaterial substrate based on CSRRs.

3.1.1 PROPOSED ANTENNA CONFIGURATION

Figure 3.1 shows the geometry of the CSRR and antenna configuration. In the proposed antenna, the solid metal ground

plane is replaced with a ground plane with periodically etched CSRRs. [20]

Figure:3.1 Configuration of the metamaterial substrate antenna


pg. 25

.

Figure:3.2 Comparison of simulated return losses between the conventional antenna and the CSRR loaded antenna for different

substrate permitivities (eps).[20]

Figure 3.2 shows the simulated return losses for three different antennas (patch antennas on conventional dielectric

substrates (єr=3 and 6) and on the metamaterial substrate loaded with CSRRs (єr=3 ). It has been noted that the CSRR

loaded antenna with єr=3 achieves the same reduction in the resonant frequency as the conventional antenna with

substrate material having a twice higher permittivity. Moreover, the bandwidth at the operating frequency is wider than

the original operating frequency. The increased bandwidth can be attributed to the reduced Q of the substrate due to the

energy leakage through the aperture in the CSRR.

3.1.2 DESIGN ANALYSIS OF A CSRR LOADED PATCH ANTENNA

Figure: 3.3 simulated Geometry of patch loaded with CSRR. Figure: 3.4 Unit cell CSRR

Unit cell parameters:

R1 = 8 mm

R2 = 5 mm

C = 2 mm

D = 1 mm


pg. 26

Figure: 3.5 (a) simulated Geometry of patch loaded with CSRR(upper layer)

Upper layer parameters:

Length = 54.775 mm

Width = 70 mm

Cut width = 5.009 mm

Cut depth = 9.9 mm

Figure:3.5(b) simulated Geometry of patch loaded with CSRR(bottom layer)

CSRR array parameters:

Length of the CSRR array = 86 mm

width of the CSRR array = 50 mm


pg. 27

Figure: 3.6(a) Photograph of the fabricated antenna (Upper layer) Figure: 3.6(b) Photograph of the fabricated antenna

(Upper layer)

Figure: 3.7(a) Photograph of the fabricated antenna (bottom layer) Figure 3.7(b) Photograph of the fabricated antenna

(bottom layer)

Return loss is measured using a spectrum analyzer. Numerical calculations of the Return loss is performed using the

Method of Moments (Mom) based electromagnetic solver IE3D commercial software. Measured and simulated return

losses are presented in Figure 2.6(a) & 2.6(b), which exhibits a good agreement. Some minor discrepancies between the

measured and simulated return loss values can be attributed to some impedance mismatches as a result coax-to-microstrip

transitions connector side and also imperfections in fabrication process.


pg. 28

Figure: 3.8 Return loss Vs freq of a normal patch antenna

Figure: 3.9 Return loss vs frequency of CSRR loaded patch antenna


pg. 29

Figure: 3.10 Angle Vs freq showing phase change at 1.4 GHz of a metamaterial(CSRR) loaded patch antenna.

Figure: 3.11 comparative graph of return loss Vs frequency

3.13 CONCLUDING REMARKS

A compact microstrip antenna with an improved bandwidth using a metamaterial substrate based on complimentary split

ring resonators has been presented. For the characterization of the microstrip antennas on metamaterial substrates, the

effective medium approach was employed. The new design help achieve the reduction of the antenna size and the

improvement of the bandwidth for microstrip patch antennas. The results presented in this chapter are promising for the

design of compact antennas achieving a size reduction without having to sacrifice the antenna bandwidth, which makes

the antenna useful for various applications.


pg. 30

CHAPTER FOUR

COMPACT DUAL FREQUENCY WIDE BAND CIRCULAR PATCH ANTENNA WITH U-SLOT

4.1 INTRODUCTION

In this chapter, we have reported the performance of a compact inset-feed circular patch antenna with U-shaped

slot and its performance is compared with that of a simple circular patch antenna designed under identical conditions. The

radiation properties of a circular patch antenna with U slot designed on glass epoxy FR-4 substrate are obtained and

compared with that of a normal circular patch antenna designed under identical conditions. The modified antenna not only

resonates at two different frequencies (2.567-2.733 GHz) but also presents marked improvement in the bandwidth (3 dB

bandwidth 400 MHz). return loss and VSWR of antenna as a function of frequency are simulated using conventional

software Zeeland‟s IE3D method of moment and has been compared with the network analyzer measured value of return

loss Vs frequency. while radiation patterns of the modified structure are simulated to present in this paper.

4.1.1 PROPOSED ANTENNA GEOMETRY

Geometry and inset feed arrangement of a circular patch antenna with U-shaped slot is shown in figure4.I. The

circular patch antenna with radius 'r' = 1.4 cm is designed on a glass epoxy FR-4 substrate having substrate thickness 'h' =

1.6mm, relative dielectric constant = 4.4 and loss tangent tan β= 0.02. The patch lie in the XY plane over a large

rectangular ground plane. the resonance frequency of a simple circular patch antenna for TM10 mode of excitation is

2.877 GHz while measured results with this antenna indicate that antenna is resonating at single frequency 2.86GHz.

These two frequency values are quite close to each other. The measured VSWR of this antenna is 1.15. These results

indicate good matching of antenna geometry with the feed network.

Figure: 4.1 Proposed Geometry of circular patch antenna with U slot [5]


pg. 31

4.1.2 DESIGN OF CIRCULAR PATCH ANTENNA

The circular patch antenna with radius 'r' = 1.4 cm is designed on a glass epoxy FR-4 substrate having

substrate thickness 'h' = 1.6 mm, relative dielectric constant = 4.4 and loss tangent tan β = 0.02. The patch lie in the XY

plane over a large rectangular ground plane

< ------2.8 c.m ------------ >

Feed point : 3,-5.5

Figure:4.2 simple circular patch antenna

Figure: 4.3 Variation of return loss with frequency for a circular patch antenna


pg. 32

4.1.3 DESIGN OF CIRCULAR PATCH ANTENNA WITH U SLOT :

A U slot has been made on the same circular patch antenna with radius 'r' = 1.4 cm is designed on a glass epoxy

FR-4 substrate having substrate thickness 'h' = 1.6mm, relative dielectric constant = 4.4 and loss tangent tan β = 0.02. The

patch lie in the XY plane over a large rectangular ground plane. The structure is simulated by IE3D using method of

moment technique having feed point at 3,-5.5 and its response of return loss Vs frequency is analyses.

-----> I 5 mm I <---

Figure: 4.4 circular patch antenna with U slot made at the patch.

Upper structure

Figure: 4.5 photograph of U slot circular patch antenna (top layer)

Figure: 4.6 photograph of U slot circular patch antenna (bottom layer)


pg. 33

Figure: 4.7 Variation of return loss with frequency for a circular patch antenna with U slot made at the patch.

Figure 4.8 comparative graph of return loss Vs frequency

Figure 4.9 variation of VSWR with frequency


pg. 34

On application of U-shaped slot in the circular patch geometry with dimensions LI = 1.05cm, L2 = 0.95cm, WI =

0.5cm, and W2 = 0.l cm, the antenna now resonates at two different frequencies (2.568 and 2.677 GHz) which are smaller

than that obtained with a simple circular patch antenna. The variations in return loss and VSWR with frequency are shown

in figures 4.7 , 4.8 and 4.9. VSWR of antenna is close to unity at the frequency of interest as shown in the figure 4.9

which again confirms excellent matching of this antenna with feed network.

4.1.4 CONCLUDING REMARKS

The return loss of a circular patch antenna with U shaped slot is investigated in free space and is compared with

that of a simple circular patch antenna excited under similar conditions. The modified antenna resonates at two different

frequencies with improved bandwidth. The two resonance frequencies are in the lower band of frequencies allotted for

Wi-Fidelity systems by IEEE 802.16 working group. The verification of other results through experimental results is stil l

going on.


pg. 35

CHAPTER FIVE

CONCLUSION AND SUGGESTIONS FOR FUTURE WORK

5.1 CONCLUDING REMARKS

Microstrip patch antenna can provide printed radiating structure, which are electrically thin, lightweight and low

cost, is a relatively not too old. The development of system such as Satellite communication, highly sensitive radar, radio

altimeters and Missiles systems needs very light weight antenna which can be easily attached with the systems and not

make the system bulky. These requirements are main factors to the development of the microstrip patch antenna. By doing

this we can get required results.

Rectangular and circular microstrip patch antenna are most common and very easy to analysis but to enhance

their bandwidth, and to achieve multiband operation we need to make some slots on the patch and to work on defected

ground structure, defected microstrip structure and meta-material.

5.2 SUGGESTION FOR FUTURE WORKS

In future also, as per requirement many new shapes can replace the conventional shapes .There are many shapes

in the field of microstrip patch antenna .A design of slots on the patch and making defected structure in the ground plane

for improving the bandwidth as well as achieving the multiband operation which is the part of this project is very good

for future aspects. All works has been performed in the thesis with the IE3D simulation software.

An interesting feature of a CSRR loaded patch antenna which would be my future area of work is the zeroth

order resonance [16], which could be observed by simulating the CSRR loaded patch antenna at different resonant

frequency. Observing zeroth order resonance could be utilized for designing multiband antennas.

As we have seen the utility of U slot antenna for achieving the wideband as well as multiband operation. This

advantage can further be enhanced by using double U slot antenna.


pg. 36

REFERENCES

[1] S. A. Schelkunoff, H.T.Friss, Antennas: Theory and Practice, New York: John Willy & Sons, 1952. [2 ] G. A. Deschamps, “ Microstrip Microwave Antennas”, presented at Third USAF symposium on Antennas, 1953.

[3] J. Brown, “Artificial dielectrics,” Progress in Dielectrics, vol. 2, pp. 195–225, 1960.

[4] V. G. Veselago,“The electrodynamics of substances with simultaneously negative values of epsilon and mu,” Sov. Phys.

Uspekhi, 10, pp. 509-514, 1968.

[5] Y.T. Lo, Theory and experiment on microstrip antennas, IEEE Trans.Antennas Propag 27, pp.137–145. 1979

[6] J.S. Colburn and Y. Rahmat-Samii, patch antennas on externally perforated high dielectric permittivity material, electron Lett.

31,pp.1710–1712. 1995

[7] C. A. Balanis, “Antenna Theory, Analysis and Design,” John Wiley & Sons, New York, 1997.

[8] J. B. Pendry, A. J. Holden, D. J. Robbins, and W. J. Stewart, “Magnetism from conductors and enhanced nonlinear phenomena,” IEEE Trans. Microw. Theory Tech. 47, pp. 2075-2081, 1999.

[9] R Garg, P Bhartia, I Bahl, and A. Lttipiboon, Microstrip antenna design handbook, Artech House, 2000.

[10] J. B. Pendry, “Negative Refraction Makes a Perfect Lens,” Phys. Rev. Lett. 85,pp.3966-3969, 2000.

[11] A. Shelby, D. R. Smith, S. Schultz, “Experimental verification of a negative index of refraction,” Science, 292, pp. 77–79, 2001.

[12] R. Marques, F. Mesa, J. Martel, and F. Median, Comparative analysis of edge and broadside coupled split ring resonators for

metamaterial design-Theory and experiment, IEEE Trans. Antennas Propag.51,pp 2572–2581.2003,

[13] D.R. Smith, J.B. Pendry, and M.C.K.Wiltshire, Metamaterials and negative refractive index, Science, 305, pp.788–792. 2004,

[14] F. Falcone, T. Lopetegi, M. A. G. Laso, J. D. Baena, J. Bonache, M. Beruete, R. Marques, F. Martin, M. Sorolla, “Babinet

Principle Applied to the Design of Metasurfaces and Metamaterials,” Phys. Rev. Lett. 93, 197401, 2004.

[15] F. Falcone, T. Lopetegi, J.D. Baena, R. Marques, F. Martin, and M. Orolla, Effective Negative є stopband microstrip lines based

on complimentary split ring resonators, IEEE Microwave Wireless Compon. Lett. 14,pp.280–282. 2004 [16 ] A. Sanada, M. Kimura, I. Awai, C. Caloz, and T. Itoh, A Planar

Zeroth-Order Resonator Antenna Using A Left-handed TransmissionLine, 34th European Microwave Conference, Amsterdam, 2004.

[17] S. A. Ramakrishna, “Physics of negative refractive index materials,” Rep. Prog. Phys. 68, pp. 449–521, 2005.

[18] J.D. Baena, J. Bonache, F. Martin, R.M. Sillero, F. Falcone, T. Lopetegi, M.A.G. Laso, J. Garcia-Garcia, I. Gil, M.F.

Portillo, and M.Sorolla, Equivalent-circuit models for split-ring resonators and complementary split-ring resonators coupled to planar

transmission lines, IEEE Trans. Antennas Propag.53, 1451–1461. 2005

[19] P.M.T. Ikonen, S.I. Maslovski, C.R. Simovski, and S.A. Tretyakov, on artificial magnetodielectric loading for improving the

impedance bandwidth properties of microstrip antennas, IEEE Trans. Antennas Propag. 54, pp.1654–1662. 2006

[20] Yoonjae Lee and Yang Hao, “Characterization of microstrip patch antennas on metamaterial Substrates loaded with

complementary split-ring Resonators” Wiley Periodicals, Inc. Microwave Opt Technol. Lett. 50, pp.2131–2135, 2008.


pg. 37

A B O U T T H E A U T H O R

Sunil Kumar Thakur is presently working as Senior Scientific Officer In Director General Quality Assurance,

Department of Defense production, Ministry Of Defense (India) since Jul 2012. Till Jul 2012 he had 19 years of

working experience in Indian Air Force wherein he has been looking after induction of Surface To Air Missile

Systems in Indian Air Force and Production, Planning, Execution and its Monitoring of Missiles and Radars

systems of Russian and Indio-western origin. He has received his Bachelor of Engineering Degree in

Electronics & Communication Engineering from Institution of Engineers (India) and ME Degree in

Communication Control and Networking from the University of RGPV Bhopal, MP. He has presented 03

papers in National Conference and one paper in International Conference in the topic of Microstrip Patch

Antenna.


pg. 38

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