1

CHAPTER 1

INTRODUCTION

1.1 MICROSTRIP PATCH ANTENNA:

Microstrip patch antenna is a type of radio antenna with low profile, which

can be mounted on a flat surface. It consists of a flat rectangular sheet or patch of

metal, mounted over a larger sheet of metal called ground plain.

A patch antenna is a narrowband, wide-beam antenna fabricated by etching

the antenna element pattern in metal trace bonded to an

insulating dielectric substrate, such as a printed circuit board, with a continuous

metal layer bonded to the opposite side of the substrate which forms a ground

plane. Common Microstrip antenna shapes are square, rectangular, circular and

elliptical, but any continuous shape is possible. Some patch antennas do not use a

dielectric substrate and instead are made of a metal patch mounted above a ground

plane using dielectric spacers; the resulting structure is less rugged but has a

wider bandwidth. Because such antennas have a very low profile, are mechanically

rugged and can be shaped to conform to the curving skin of a vehicle, they are

often mounted on the exterior of aircraft and spacecraft, or are incorporated

into mobile radio communications devices.

They are usually employed at UHF and higher frequencies because

the size of the antenna is directly tied to the wavelength at the resonant frequency.

An advantage inherent to patch antennas is the ability to

have polarization diversity. Patch antennas can easily be designed to have vertical,

https://en.wikipedia.org/wiki/Light_beamhttps://en.wikipedia.org/wiki/Dielectrichttps://en.wikipedia.org/wiki/Printed_circuit_boardhttps://en.wikipedia.org/wiki/Ground_planehttps://en.wikipedia.org/wiki/Ground_planehttps://en.wikipedia.org/wiki/Bandwidth_(signal_processing)https://en.wikipedia.org/wiki/Mobile_radiohttps://en.wikipedia.org/wiki/UHFhttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Resonancehttps://en.wikipedia.org/wiki/Polarization_(waves)

2

horizontal, right hand circular (RHCP) or left hand circular (LHCP) polarizations,

using multiple feed points, or a single feed point with asymmetric patch structures.

This unique property allows patch antennas to be used in many types of

communications links that may have varied requirements.

1.1.1 RECTANGULAR PATCH:

The most commonly employed Microstrip antenna is a rectangular patch

which looks like a truncated Microstrip transmission line. It is approximately of

one-half wavelength long. When air is used as the dielectric substrate, the length of

the rectangular Microstrip antenna is approximately one-half of a free-

space wavelength. As the antenna is loaded with a dielectric as its substrate, the

length of the antenna decreases as the relative dielectric constant of the substrate

increases. The resonant length of the antenna is slightly shorter because of the

extended electric "fringing fields" which increase the electrical length of the

antenna slightly. An early model of the Microstrip antenna is a section of

Microstrip transmission line with equivalent loads on either end to represent the

radiation loss.

With the development of MIC and high frequency semiconductor devices,

Microstrip has drawn the maximum attention of the antenna community in recent

years. In spite of its various attractive features like, light weight, low cost, easy

fabrication, conformability on curved surface and so on, the Microstrip element

suffers from an inherent limitation of narrow impedance bandwidth

A WLAN is a flexible data communication network used as an extension to,

or an alternative for, a wired LAN in a building. Primarily they are used in

industrial sectors where employees are on the move, in temporary locations or

https://en.wikipedia.org/wiki/Microstriphttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Dielectric_constant

3

where cabling may hinder the installation of wired LAN. Increasingly more and

more wireless LANs are being setup in home and or home office situations as the

technology is becoming more affordable. Industry giants are already predicting that

90% of all notebooks will contain integrated WLAN by 2008. With progress and

expansion comes the need for faster technology and higher transfer rates. The

ongoing wireless LAN standardization and Research & Development activities

worldwide, which target transfer rates higher than 100 Mbps, justify the fact that

WLAN technology will play a key role in wireless data transmission. Cellular

network operators have recognized this fact, and strive to exploit WLAN

technology and integrate this technology into their cellular data networks.

4

CHAPTER 2

FEEDING TECHNIQUES

Feeding technique influences the input impedance and polarization

characteristics of the antenna. There are three most common structures that are

used to feed planar printed antennas. These are coaxial probe feeds, Microstrip line

feeds, and aperture coupled feeds. With coaxial probe feed the centre conductor of

the coaxial connector is soldered to the patch. The coaxial fed structure is often

used because of ease of matching the characteristic impedance to that of the

antenna. Along with this, the parasitic radiation from the feed network tends to be

insignificant. Microstrip line-fed structures are more suitable compared to probe

feeds, due to ease of fabrication and lower costs. Serious drawbacks of this feed

structure are the strong parasitic radiation and it requires a transformer, which

restricts the broadband capability of the antenna. The aperture-coupled structure

has all of the advantages of the former two structures and isolates the radiation

from the feed network thereby leaving the main antenna radiation uncontaminated.

5

2.1 TYPES OF FEEDING TECHNIQUES:

A feed line is used to excite to radiate by direct or indirect contact. There are

many different methods of feeding and 4 most popular methods are:

Microstrip line feed

Co-axial probe

Aperture coupling

Proximity coupling

2.1.1 MICROSTRIP LINE FEEDING:

Microstrip line feed is one of the easier methods to fabricate as it is a just

conducting strip connecting to the patch and therefore be considered as extinction

of patch. It is simple to model and easy to match by controlling the insert position..

Microstrip line feed is a conducting strip that is connected directly to the

edge of the Microstrip patch. It has an advantage that the feed can be etched on the

same substrate to provide a planar structure. However the disadvantage of this

method is that as substrate thickness increases, surface wave and spurious feed

radiation increases which limit the bandwidth

2.1.2 CO-AXIAL FEEDING:

Microstrip antennas can also be fed from underneath via a probe. Co-axial

feeding is feeding method in which the inner conductor of the co-axial is attached

to the radiation patch of the antenna while the outer conductor is connected to the

6

ground plane (ie) the outer conductor of the coaxial cable is connected to the

ground plane, and the center conductor is extended up to the patch antenna.

FIG 2.1: Coaxial cable feed of patch antenna.

The position of the feed can be altered as before (in the same way as the

inset feed, above) to control the input impedance.

The coaxial feed introduces an inductance into the feed that may need to be

taken into account if the height h gets large (an appreciable fraction of a

wavelength). In addition, the probe will also radiate, which can lead to radiation in

undesirable directions.

The Advantages are

Easy to fabricate

Easy to match

Low spurious radiation

The Disadvantages are

Narrow bandwidth

7

Difficult to model specially for thick substrate

Possess inherent asymmetries which generate higher order

modes which produce cross polarization radiation.

2.1.3 APERTURE COUPLING:

Another method of feeding Microstrip antennas is the aperture feed. In this

technique, the feed circuitry (transmission line) is shielded from the antenna by a

conducting plane with a hole (aperture) to transmit energy to the antenna. Aperture

coupling consists of two different substrate separated by a ground plane. On the

bottom side of the lower substrate there is a Microstrip feed line whose energy is

coupled to the patch through a slot on the ground plane separating two substrates.

This arrangement allows independent optimization of the feed mechanism and the

radiating element. Normally top substrate uses a thick low dielectric constant

substrate while for the bottom substrate; it is the high dielectric substrate. The

ground plane, which is in the middle, isolates the feed from radiation element and

minimizes interferences of spurious radiation for pattern formation and

polarization purity.

FIG 2.2: Aperture coupled feed.

8

The upper substrate can be made with a lower permittivity to produce

loosely bound fringing fields, yielding better radiation. The lower substrate can be

independently made with a high value of permittivity for tightly coupled fields that

don't produce spurious radiation. The disadvantage of this method is increased

difficulty in fabrication.

The Advantages are

Allows independent optimization of fed mechanism element.

2.1.4 PROXIMITY COUPLING:

Proximity coupling has the largest bandwidth, has low spurious radiation.

However fabrication is difficult. Length of the feeding stub and width - to - length

ratio of patch is used to control the match.

2.1.5 INSET FEED:

Input impedance could be reduced by inserting an inset feed closer to the

centre of the patch. So this is used to tune the input impedance to the desired value.

Typically patch antenna yields a high input impedance, the current is low at the

ends of a half-wave patch and increases in magnitude towards the centre, the input

impedance (Z=V/I) could be reduced if the patch was fed closer to the centre. One

method of doing this is by using an inset feed (a distance R from the end). Since

the current has a sinusoidal distribution, moving in a distance R from the end will

increase the current by cos (pi*R/L) – this is just nothing that the wavelength is

2*L, and so the phase difference is 2*pi*R/(2*L)=pi*R/L.

9

The voltage also decreases in magnitude by the same amount that the current

increases. Hence, using Z=V/I, the input impedance scales as:

Zin (R) = cos2(

𝜋𝑅

𝐿) Zin(0)

In the above equation, Zin(0) is the input impedance if the patch was feed at

the end. Hence, by feeding the patch antenna as shown, the input impedance can be

decreased. As an example, if R=L/4, then cos (pi*R/L)= cos (pi/4), so that

[cos(pi/4)]^2=1/2. Hence, a (1/8) – wavelength inset would decrease the input

impedance by 50%. This method can be used to tune the input impedance to the

desired value.

2.1.5.1 FED WITH A QUARTER-WAVELENGTH TRANSMISSION LINE

The Microstrip antenna can also be matched to a transmission line of

characteristic impedance Z0 by using a quarter-wavelength transmission line of

characteristic impedance Z1.

FIG 2.3:Patch antenna with a quarter-wavelength matching section

10

The goal is to match the input impedance (Zin) to the transmission line (Z0).

If the impedance of the antenna is ZA, then the input impedance viewed from the

beginning of the quarter-wavelength line becomes

This input impedance Zin can be altered by selection of the Z1, so that

Zin=Z0 and the antenna is impedance matched. The parameter Z1 can be altered

by changing the width of the quarter-wavelength strip. The wider the strip is, the

lower the characteristic impedance (Z0) is for that section of line.

2.1.6 COUPLED (INDIRECT) FEEDS:

The feeds above can be altered such that they do not directly touch the

antenna. For instance, the probe feed can be trimmed such that it does not extend

all the way up to the antenna. The inset feed can also be stopped just before the

patch antenna.

11

FIG 2.4: Coupled (indirect) inset feed.

The advantage of the coupled feed is that it adds an extra degree of freedom

to the design. The gap introduces a capacitance into the feed that can cancel out the

inductance added by the probe feed.

12

CHAPTER 3

FOUNDATIONS FOR MICROSTRIP DESIGN

A Microstrip patch antenna is a radiating patch on one side of a dielectric

substrate, which has a ground plane on the underside. The EM waves fringe off the

top patch into the substrate, reflecting off the ground plane and radiates out into the

air. Radiation occurs mostly due to the fringing field between the patch and

ground.

FIG 3.1: Operations of a Microstrip Patch

The radiation efficiency of the patch antenna depends largely on the

permittivity (εr) of the dielectric. Ideally, a thick dielectric, low εr and low insertion

loss is preferred for broadband purposes and increased efficiency. The advantages

13

of Microstrip antennas are that they are low-cost, conformable, light weight and

low profile, while both linear and circular polarization is easily achieved. These

attributes are desirable when considering antennas for WLAN systems. Some

disadvantages include such as a narrow bandwidth as well as a low gain (~6 dB)

and polarization purity is hard to achieve.

3.1 POLARIZATION TYPES:

This is the polarization of the wave radiated by the antenna in that particular

direction. This is usually dependant on the feeding technique. When the direction

is not specified, it is in the direction of maximum radiation. Shown below are two

most widely used polarization types.

3.1.1 LINEAR POLARIZATION:

A slot antenna is the counterpart and the simplest form of a linearly

polarized antenna. On a slot antenna the E field is orientated perpendicular to its

length dimension. The usual Microstrip patches are just different variations of the

slot antenna and all radiate due to linear polarization. The operations of a linearly

polarized wave radiating perpendicular to the patch plane.

14

FIG 3.2: Linear Polarization

3.1.2 CIRCULAR POLARIZATION:

Circular polarization (CP) is usually a result of orthogonally fed signal input.

When two signals of equal amplitude but 90 degree phase shifted the resulting

wave is circularly polarized. Circular polarization can result in Left hand circularly

polarized (LHCP) where the wave is rotating anticlockwise, or Right hand

circularly polarized (RHCP) which denotes a clockwise rotation. The main

advantage of using CP is that regardless of receiver orientation, it will always

receive a component of the signal. This is due to the resulting wave having an

angular variation.

15

FIG 3.3: Circular Polarization

3.2 BANDWIDTH:

The bandwidth of the patch is defined as the frequency range over which it

is matched with that of the feed line within specified limits. In other words, the

frequency range over which the antenna will perform satisfactorily. This means the

channels have larger usable frequency range and thus results in increased

transmission. The bandwidth of an antenna is usually defined by the acceptable

standing wave ratio (SWR) value over the concerned frequency range.

16

FIG 3.4: Narrowband vs. Broadband

Most commercial antennas use a 1.5:1 ratio, suggesting that the range that is

covered between the SWR of 1 up to 1.5 is the bandwidth. To ensure comparability

with the commercial products, a decision was made to use a 1.5:1 ratio to calculate

the bandwidth of antennas.

17

FIG 3.5: Bandwidth Measurement

18

CHAPTER 4

DESIGN METHODOLOGY FOR RECTANGULAR PATCH

4.1 ANTENNA SHAPE:

In its most basic 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. 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.

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.

FIG 4.1: Structure of Microstrip Patch Antenna

19

4.2 METHOD OF ANALYSIS:

Transmission line model represents the Microstrip antenna by two slots of

width W and height h, separated by a transmission line of length L. The Microstrip

is essentially a non-homogeneous line of two dielectrics, typically the substrate and

air.

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 electric-

magnetic (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 (εreff) must

be obtained in order to account for the fringing and the wave propagation in the

line.

FIG 4.2: Electric Field Lines

The value of (εreff) 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.

εreff = 𝜀𝑟+1

2 +

𝜀𝑟−1

2 [1+12

ℎ

𝑊 ]1/2

20

Where,

εreff= Effective dielectric constant

εr = Dielectric constant of substrate

h= Height of dielectric substrate

W= Width of the patch

Consider, 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.

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 λ0/√εreff.

where,

λ0 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 4 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.

21

FIG 4.3: Microstrip Patch Antenna

It is seen 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 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.

22

FIG 4.4: Top View of Antenna

∆L = 0.412 (εreff±0.3)(

W

h+0.264)

(εreff−0.258)(W

h+0.8)

The effective length of the patch Leff now becomes:

Leff = L+2∆L

For a given resonance frequency f0 , the effective length is

Leff = 𝑐

2𝑓0 √εreff

23

For a rectangular Microstrip patch antenna, the resonance frequency for any

TMmn mode is

f0 = 𝑐

2√εreff [(

𝑚

𝐿)2 + (

𝑛

𝑊)2]

1

2

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

For efficient radiation, the width W is

W = 𝑐

2𝑓0 √(εr+1)

2

4.3 FEED POINT:

4.3.1 MICROSTRIP INSET FEED:

Previously, the patch antenna was fed at the end as shown here. Since this

typically yields a high input impedance, we would like to modify the feed. Since

the current is low at the ends of a half-wave patch and increases in magnitude

toward the center, the input impedance (Z=V/I) could be reduced if the patch was

fed closer to the center. One method of doing this is by using an inset feed (a

distance R from the end).

http://www.antenna-theory.com/antennas/patches/patch.php

24

FIG 4.5: Patch Antenna with an Inset Feed.

Since the current has a sinusoidal distribution, moving in a distance R from

the end will increase the current by cos(pi*R/L) - this is just noting that the

wavelength is 2*L, and so the phase difference is 2*pi*R/(2*L) = pi*R/L.

The voltage also decreases in magnitude by the same amount that the current

increases. Hence, using Z=V/I, the input impedance scales as:

In the above equation, Zin(0) is the input impedance if the patch was fed at

the end. Hence, by feeding the patch antenna as shown, the input impedance can be

decreased. As an example, if R=L/4, then cos(pi*R/L) = cos(pi/4), so that

[cos(pi/4)]^2 = 1/2. Hence, a (1/8)-wavelength inset would decrease the input

25

impedance by 50%. This method can be used to tune the input impedance to the

desired value.

The feed mechanism plays an important role in the design of Microstrip

patch antennas. A Microstrip patch antenna can be fed either by coaxial probe or

by an inset Microstrip line. Coaxial probe feeding is sometimes advantageous for

applications like active antennas, while Microstrip line feeding is suitable for

developing high-gain Microstrip array antennas. In both cases, the probe position

or the inset length determines the input impedance.

The input impedance behavior for a coaxial probe-fed patch antenna has

been studied analytically by means of various models, including the transmission-

line model and the cavity model, and by means of full-wave

analysis. Experimentally and theoretically, it has been found that a coaxial-probe

fed-patch antenna's input impedance exhibits behavior that follows the

trigonometric function:

cos2(π𝑦0

𝐿)

Where;

L = the length of the patch and

y0 = the position of the feed from the edge along the direction of the patch length

L.

On the other hand, it has been found experimentally4 that on low-dielectric-

constant materials, the input impedance of an inset-fed probe antenna exhibits

fourth-order behavior following the function:

26

cos4(π𝑦0

𝐿)

Fortunately, a simple analytical approach has been developed using the

transmission-line model to find the input impedance of an inset-fed Microstrip

patch antenna. Using this approach, a curve-fit formula can be derived to find the

inset length to achieve a 50-Ω input impedance when using modern thin dielectric

circuit-board materials.

FIG 4.6

This is a graphical depiction of an inset-fed Microstrip patch antenna. The

parameters εr, h, L, W, wf, and y0, respectively, are used to denote substrate

27

dielectric constant, thickness, patch length, patch width, feed-line width, and feed-

line inset distance. The input impedance of an inset-fed Microstrip patch antenna

depends mainly on the inset distance, y0, and to some extent on the inset width (the

spacing between the feed line and the patch conductor). Variations in the inset

length do not produce any change in resonant frequency, but a variation in the inset

width will result in a change in resonant frequency. Hence, in the following

discussion, the spacing between the patch conductor and feed line is kept constant,

equal to the feed line's width; variations in the input impedance at resonant

frequency with respect to inset length will studied as a function of various

parameters.

4.4 DIELECTRIC SUBSTRATE:

Considering the trade-off between the antenna dimensions and its

performance, it was found suitable to select a thin dielectric substrate with low

dielectric constant. Thin substrate permits to reduce the size and also spurious

radiation as surface wave, and low dielectric constant − for higher bandwidth,

better efficiency and low power loss. The simulated results were found

satisfactory.

28

CHAPTER 5

DESIGN METHODOLOGY FOR MINKOWSKI FRACTAL STRUCTURE

Fractal antenna is an antenna that uses a fractal , self-similar design to

maximize the length or increase the perimeter of material that can transmit or

receive electromagnetic radiation within a given total surface area or volume.

An important property of any fractal geometry is the possibility of obtaining

an arbitrarily long curve confined in a given space. This property can be exploited

effectively in the process of antenna miniaturization. Another interesting property

of fractal geometry is the self-similarity property. Self similarity can be described

as the replication of the geometry of the structure at a different scale within the

same structure. Self similarity property of fractals may result in multiband

behavior of the fractal shaped antennas. The iterative-generation procedure for a

Minkowski island fractal is depicted.

FIG 5.1: Iterative generation Procedure for a Minkowski Fractal

29

The fractal is formed by displacing the middle one-third of each straight

segment (indentation length) by some fraction called the indentation width.

Indentation factor (i) is defined here as the ratio of indentation width to the

indentation length. The resulting structure has five segments for every one of the

previous iteration, but not all of the same scale. Changing the indentation factor

causes a shift in the resonant frequencies, so proper tuning of the indentation factor

is necessary to obtain the frequencies required for WiMAX and Bluetooth

applications.

5.1 ANTENNA DESIGN PROCEDURE AND MODELLING:

To start with, rectangular shaped wearable antenna is designed with the

specifications using CST Microwave Studio 2010. The antenna is fed through an

aperture using Microstrip line. Width of the Microstrip line is calculated for 50

ohm characteristic impedance and its length beyond the aperture is optimized to

achieve best impedance matching. Size of the ground plane and the substrate is

taken as 76.8mm X 57.8mm. The patch layer and the ground plane of the antenna

are made up of conductive fabrics having thicknesses of 1.8mm (Flame Retardant,

FR4). The patch dimensions for each of the antenna are optimized to get a

resonance frequency of 2.4 GHz. This constitutes the basic design for zeroth

iteration of the fractal geometry for the antenna under consideration and to be used

for WiMAX and Bluetooth applications.

30

5.2 DESIGN SPECIFICATIONS OF ANTENNA:

DESIGN PARAMETER VALUE

Resonant frequency (GHz) 2.4

Substrate dielectric constant 1.44

Substrate thickness(mm) 1.8

Substrate material FR4

TABLE 5.1: DESIGN SPECIFICATIONS OF ANTENNA

31

CHAPTER 6

DESIGN METHODOLOGY FOR DMS STRUCTURE

A Defected Microstrip Structure (DMS) is proposed to reduce the size of a

rectangular patch antenna by increasing its electric length, without degrading its

performance.

Currently, patch antennas have become one of the principal goals in radio-

frequency and microwave system design because of their inherent characteristics.

Circuit-size reduction is another goal in order to provide a higher scale of

integration and portability, and patch antennas are a great option for this purpose.

In the present work, a defected Microstrip structure is proposed, which

behaves in a very similar way to that obtained when a one-cell Defected Ground

Structure (DGS) is used, but without any leakage through the ground plane.

Lately, the DGS has been widely employed to reduce the filter size, as well

as in amplifier implementations.

Moreover, the associated inductance of a conventional DGS is, at times, not

high enough to provide the required electric length by increasing the current path

in a certain application. Therefore, several works have been presented in which

the conventional defected ground structure is modified to obtain an increment in

the associated inductance, in such a way that the resulting electric length is bigger.

This proposed defected Microstrip line is an alternative for increasing the electric

length of certain circuits but without any manipulation of the ground plane.

32

With the inductance increment, a reduction in circuit dimensions can be

achieved, firstly applied in filter design. However, the DGS behavior has not been

used in patch-antenna size reduction, since most reported applications of DGS in

patch antennas are related to harmonic suppression and bandwidth improvement.

To reduce the antenna size, a shape modification short-circuited λ /4 antenna has

been reported, which is inherently of smaller size than the conventional one, but

radiation efficiency, gain, and radiation pattern are modified.

In this work, the Defected Microstrip Structure (DMS) behavior is proposed

to reduce the antenna size by introducing a defect in a conventional patch.

Moreover, this method can also be used in other rectangular patch antennas like

conventional λ /4 patch antennas, adding an extra size reduction.

6.1 DEFECTED RECTANGULAR PATCH ANTENNA :

The proposed defected antenna is designed to perform at 2.4 GHz. The slots

can be observed along the antenna length L, that is, along the non-radiating edges.

In this position, the slots can avoid any interference or modification in the

radiation pattern.

In this case, the dimension W was obtained after an optimization procedure

to avoid high cross-polarization levels, thus we obtain a relation W/L. The antenna

dimensions are W =39.4 mm, L =28.9 mm, Ls = 10 mm, and Ws =1.0 mm. Le is

set to 9.25 mm. We is set to 2 mm. The substrate used is FR4, with dielectric

constant of 1.44 and thickness of 1.8 mm. The simulation and optimization

process were done using HFSS by Ansoft.

33

Meanwhile, the simulated far-field gain pattern of both antennas is depicted.

In this figure, a comparison can be made when the elevation angle ф is zero. It is

observed that the radiation pattern in the E-plane is almost the same in both

antennas.

FIG 6.1: T-SLOT DMS STRUCTURE

6.2 SOFTWARE FOR SIMULATION:

The software used to model and simulate the Microstrip patch antenna was

HFSS (High Frequency Structural Stimulator). HFSS is a commercial finite

element method solver for electro-magnetic structures from Ansys. It is one of

several commercial tools used for antenna design, and design of RF electronic

circuit elements including filters, transmission lines and packaging. HFSS is a

34

high-performance full-wave electromagnetic (EM) field simulator for arbitrary 3D

volumetric passive device modeling that takes advantage of the familiar Microsoft

Windows graphical user interface. Ansoft HFSS employs the Finite Element

Method (FEM), adaptive meshing, and brilliant graphics to give you unparalleled

performance and insight to all of your 3D EM problems. Ansoft HFSS can be used

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

HFSS is an industry – standard stimulation tool for 3D- full wave electromagnetic

field stimulation. It is essential for the design of high frequency and high speed

component.

35

CHAPTER 7

DESIGN PARAMETERS FOR PATCH ANTENNA

7.1 DESIGN FLOW:

FIG 7.1: DESIGN FLOW

36

7.2 DESIGN SPECIFICATION:

The three essential parameters for the design of a rectangular Microstrip

Patch Antenna are:

Frequency of Operation

The resonant frequency of the antenna must be selected appropriately. The

resonant frequency selected for my design is 2.4 GHz.

Dielectric constant of the substrate (εr)

The dielectric material selected for my design is FR4which has a dielectric

constant of 1.44.

Height of dielectric substrate (h)

Because of using FR4, so height of dielectric substrate is 1.8 mm.

So, the essential parameters for the design are :

fO : 2.4 GHz

εr: 1.44

h : 1.8 mm

7.3 DESIGN PROCEDURE:

The transmission line model will be used to design the antenna.

Calculation the wavelength (λ) :

Because c = 3x108 and fo = 2.4 GHz,

So, λ = c/fo

By substituting c = 3x108 and fo = 2.4 GHz, we get;

λ=0.125m=125mm

37

Calculation of the Width (W) :

The width of the Microstrip patch antenna with substituting εr = 1.03, we get;

W=39.4mm

Calculation of Effective dielectric constant (εreff) :

The effective dielectric constant, with substituting h =1.8mm and W=39.4mm, we

get;

εreff =1.023

Calculation of the Effective length (Leff):

The Effective length with substituting εreff =1.023, we get;

Leff =25.9mm

Calculation of the length extension (ΔL):

The length extension with substituting Leff =25.9mm, we get;

ΔL=7.78mm

Calculation of actual length of patch (L):

The actual length of patch with substituting Leff =25.9mm and ΔL=7.78mm, we

get;

L=28.9mm

Calculation of the ground plane dimensions (L(g) and W(g)) The

transmission line model is applicable to infinite ground planes only. However, for

practical considerations, it is essential to have a finite ground plane. Finite and

38

infinite ground plane can be obtained if the size of the ground plane is greater than

the patch dimensions by approximately six times the substrate thickness all around

the periphery. Hence, for this design, the ground plane dimensions would be given

as:

L(g)=6h+L=6(1.8)+28.9mm=39.7mm

W(g)=6h+W=6(1.8)+39.4mm=50.2mm

39

CHAPTER 8

DESIGN ANALYSIS

8.1 SIMULATION DESIGNS:

FIG 8.1: STRUCTURE OF PATCH ANTENNA

40

FIG 8.2: PATCH ANTENNA WITH FRACTAL STRUCTURE

FIG 8.3: FINAL DESIGN

41

8.2 SIMULATION RESULTS:

8.2.1 S-PARAMETERS:

S-parameters describe the input-output relationship between ports (or

terminals) in an electrical system. For instance, if we have 2 ports (intelligently

called Port 1 and Port 2), then S12 represents the power transferred from Port 2 to

Port 1. S21 represents the power transferred from Port 1 to Port 2. In general, SNM

represents the power transferred from Port M to Port N in a multi-port network.

A port can be loosely defined as any place where we can deliver voltage and

current. So, if we have a communication system with two radios (radio 1 and radio

2), then the radio terminals (which deliver power to the two antennas) would be the

two ports. S11 then would be the reflected power radio 1 is trying to deliver to

antenna 1. S22 would be the reflected power radio 2 is attempting to deliver to

antenna 2. And S12 is the power from radio 2 that is delivered through antenna 1 to

radio 1. Note that in general S-parameters are a function of frequency (i.e. vary

with frequency).

As an example, consider the following two-port network:

FIG 8.4: TWO-PORTNETWORK

42

In the above Figure, S21 represents the power received at antenna 2 relative

to the power input to antenna 1. For instance, S21=0 dB implies that all the power

delivered to antenna 1 ends up at the terminals of antenna 2. If S21=-10 dB, then if

1 Watt (or 0 dB) is delivered to antenna 1, then -10 dB (0.1 Watts) of power is

received at antenna 2.

If an amplifier exists in the circuitry, then S21 can show gain (i.e. S21 > 0

dB). This means that for 1 W of power delivered to Port 1, more than 1 W of

power is received at Port 2.

In practice, the most commonly quoted parameter in regards to antennas is S11.

S11 represents how much power is reflected from the antenna, and hence is known

as the reflection coefficient (sometimes written as gamma: or return loss. If

S11=0 dB, then all the power is reflected from the antenna and nothing is radiated.

If S11=-10 dB, this implies that if 3 dB of power is delivered to the antenna, -7 dB

is the reflected power. The remainder of the power was "accepted by" or delivered

to the antenna. This accepted power is either radiated or absorbed as losses within

the antenna. Since antennas are typically designed to be low loss, ideally the

majority of the power delivered to the antenna is radiated.

43

FIG 8.5: S11 PLOT FOR RECTANGULAR PATCH ANTENNA

FIG 8.6: S11 PLOT FOR FRACTAL DESIGN

0.00 1.00 2.00 3.00 4.00 5.00 6.00Freq [GHz]

-20.00

-17.50

-15.00

-12.50

-10.00

-7.50

-5.00

-2.50

0.00

Y1

HFSSDesign1XY Plot 1 ANSOFT

m1

m2

Curve Info

dB(St(feed_T1,feed_T1))Setup1 : Sw eep

dB(St(feed_T1,feed_T1))_1Imported

Name X Y

m1 2.4010 -17.0012

m2 3.6010 -12.2478

44

FIG 8.7: S11 PLOT FOR FINAL DESIGN

8.2.2 VSWR:

For a radio (transmitter or receiver) to deliver power to an antenna, the

impedance of the radio and transmission line must be well matched to the antenna's

impedance. The parameter VSWR is a measure that numerically describes how

well the antenna is impedance matched to the radio or transmission line it is

connected to.

VSWR stands for Voltage Standing Wave Ratio, and is also referred to as

Standing Wave Ratio (SWR). VSWR is a function of the reflection coefficient,

which describes the power reflected from the antenna. If the reflection coefficient

is given by , then the VSWR is defined by the following formula:

http://www.antenna-theory.com/http://www.antenna-theory.com/basics/impedance.phphttp://www.antenna-theory.com/basics/impedance.php

45

The VSWR is always a real and positive number for antennas. The smaller

the VSWR is, the better the antenna is matched to the transmission line and the

more power is delivered to the antenna. The minimum VSWR is 1.0. In this case,

no power is reflected from the antenna, which is ideal.

Often antennas must satisfy a bandwidth requirement that is given in terms

of VSWR. For instance, an antenna might claim to operate from 100-200 MHz

with VSWR

46

8.2.3 GAIN:

The term Antenna Gain describes how much power is transmitted in the

direction of peak radiation to that of an isotropic source. Antenna gain is more

commonly quoted than directivity in an antenna's specification sheet because it

takes into account the actual losses that occur.

A transmitting antenna with a gain of 3 dB means that the power received

far from the antenna will be 3 dB higher (twice as much) than what would be

received from a lossless isotropic antenna with the same input power. Note that a

lossless antenna would be an antenna with an antenna efficiency of 0 dB (or

100%). Similarly, a receive antenna with a gain of 3 dB in a particular direction

would receive 3 dB more power than a lossless isotropic antenna.

Antenna Gain is sometimes discussed as a function of angle. In this case, we

are essentially plotting the radiation pattern, where the units (or magnitude of the

pattern) are measured in antenna gain.

Antenna Gain (G) can be related to directivity (D) and antenna efficiency

by:

The gain of a real antenna can be as high as 40-50 dB for very large dish

antennas (although this is rare). Directivity can be as low as 1.76 dB for a real

antenna (example: short dipole antenna), but can never theoretically be less than 0

dB. However, the peak gain of an antenna can be arbitrarily low because of losses

or low efficiency. Electrically small antennas (small relative to the wavelength of

http://www.antenna-theory.com/basics/directivity.phphttp://www.antenna-theory.com/basics/efficiency.phphttp://www.antenna-theory.com/basics/radpattern.phphttp://www.antenna-theory.com/basics/directivity.phphttp://www.antenna-theory.com/antennas/shortdipole.php

47

the frequency that the antenna operates at) can be very inefficient, with antenna

gains lower than -10 dB (even without accounting for impedance mismatch loss).

FIG 8.9: GAIN PLOT

8.2.4 RADIATION PATTERN:

In the field of antenna design the term radiation pattern (or antenna

pattern or far-field pattern) refers to the directional (angular) dependence of the

strength of the radio waves from the antenna or other source.

Particularly in the fields of fiber optics, lasers, and integrated optics, the

term radiation pattern may also be used as a synonym for the near-

https://en.wikipedia.org/wiki/Antenna_(radio)https://en.wikipedia.org/wiki/Radio_waveshttps://en.wikipedia.org/wiki/Fiber_opticshttps://en.wikipedia.org/wiki/Laserhttps://en.wikipedia.org/wiki/Integrated_opticshttps://en.wikipedia.org/wiki/Near_and_far_field

48

field pattern or Fresnel pattern. This refers to the positional dependence of

the electromagnetic field in the near-field, or Fresnel region of the source. The

near-field pattern is most commonly defined over a plane placed in front of the

source, or over a cylindrical or spherical surface enclosing it.

The far-field pattern of an antenna may be determined experimentally at

an antenna range, or alternatively, the near-field pattern may be found using a near-

field scanner, and the radiation pattern deduced from it by computation. The far-

field radiation pattern can also be calculated from the antenna shape by computer

programs such as NEC. Other software, like HFSS can also compute the near field.

The far field radiation pattern may be represented graphically as a plot of

one of a number of related variables, including; the field strength at a constant

(large) radius (an amplitude pattern or field pattern), the power per unit solid angle

(power pattern) and the directive gain. Very often, only the relative amplitude is

plotted, normalized either to the amplitude on the antenna bore sight, or to the total

radiated power. The plotted quantity may be shown on a linear scale, or in dB. The

plot is typically represented as a three-dimensional graph (as at right), or as

separate graphs in the vertical plane and horizontal plane. This is often known as

a polar diagram.

https://en.wikipedia.org/wiki/Near_and_far_fieldhttps://en.wikipedia.org/wiki/Electromagnetic_fieldhttps://en.wikipedia.org/wiki/Near_and_far_fieldhttps://en.wikipedia.org/wiki/Antenna_measurementhttps://en.wikipedia.org/wiki/Electromagnetic_near-field_scannerhttps://en.wikipedia.org/wiki/Electromagnetic_near-field_scannerhttps://en.wikipedia.org/wiki/Numerical_Electromagnetics_Codehttps://en.wikipedia.org/wiki/HFSShttps://en.wikipedia.org/wiki/Field_strengthhttps://en.wikipedia.org/wiki/Antenna_gainhttps://en.wikipedia.org/wiki/Antenna_boresighthttps://en.wikipedia.org/wiki/Decibelhttps://en.wikipedia.org/wiki/Vertical_planehttps://en.wikipedia.org/wiki/Horizontal_plane

49

FIG 8.10: RADIATION PATTERN

8.3 COMPARISON OF SIMULATION RESULTS:

PARAMETERS

PATCH

FRACTAL

DMS

S11 PLOT

-17.0012

-31.5508

-34.7580

VSWR PLOT

1.1048

1.0543

1.0373

GAIN PLOT

3.8543

4.2504

4.4051

TABLE 8.1: COMPARISON OF SIMULATION RESULTS

50

CHAPTER 9

FABRICATION & TESTING

9.1 FABRICATED ANTENNA:

FIG 9.1: FRONT VIEW

51

FIG 9.2: BACK VIEW

9.2 TESTING TOOL:

9.2.1 N9926A FieldFox Handheld Microwave Vector Network Analyzer

KEY FEATURES AND FUNCTIONS:

14 GHz max frequency

Carry the world’s most integrated handheld T/R VNA analyzer

Expand your measurement flexibility with optional 2-port VNA, time-

domain, vector voltmeter, cable and antenna analyzer and more

Save time by simultaneously measuring all four S-parameters with a single

connection

Perform accurate testing with QuickCal, full 2-port unknown thru Cal, TRL

Easily measure average and pulse power with a USB power sensor

Lightest handheld VNA at only 6.6 lb. (3.0 kg)

52

FIG 9.3: NETWORK ANALYZER

The Applications are

S-Parameters

Distance-To-Fault

Cable Trimming

Return Loss

Insertion Loss/Gain

Power Measurements

53

9.3 TESTING RESULTS :

FIG 9.4: S11 PLOT

54

FIG 9.5: VSWR PLOT

55

9.4 CERTIFICATION FOR TESTING:

56

CHAPTER 10

CONCLUSION

The designing and fabrication of Microstrip patch antenna has been

accomplished. A number of findings have been identified during the designing and

fabricating phases. The signal strength (Gain) of Microstrip patch antenna for an

unidirectional pattern is better. The area of Microstrip patch antenna is about

76.8mm * 57.8mm. There is still back lobe in radiation pattern of Microstrip

antenna. In this design, miniaturization of antennas is achieved by the use of

Minkowski fractal structure of the 1st and 2nd iterations. The material used for the

design of Minkowski fractal shaped antenna is Flame Retardant (FR4) material. In

the zeroth iteration, the antenna dimensions are chosen to suit for Bluetooth and

WiMAx applications. In the 1st and 2nd iterations the fractal geometry parameters

are tuned for optimal performance in the WiMAX and Bluetooth bands

respectively with achievement of compactness as an additional feature. In the two

frequency bands, the designed antenna gives good performance characteristics. The

DMS phenomenon is employed to reduce the physical dimensions of a rectangular

patch antenna, without degrading its radiation pattern, as well as its VSWR at the

resonant frequency (2.4 GHz). Moreover, by avoiding any etching in the ground

plane, any increasing leakage through the plane which could interfere with another

circuit of the system is not allowed. An area reduction factor of 22% was obtained.

Good agreement between the measured and simulated results was obtained for the

Microstrip patch antenna with Minkowski fractal and DMS structures.

57

10.1 COMPARISON OF RESULTS:

PARAMETER

SIMULATED VALUE

MEASURED VALUE

S11 PLOT

-34.7580 dB

-26.55 dB

VSWR PLOT

1.0373

1.369

TABLE 10.1: COMPARISON OF RESULTS

58

CHAPTER 11

REFERENCES

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NJ: John Wiley, 2005

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3. A proposed defected Microstrip structure (DMS) behavior for reducing

rectangular patch antenna size,IEEE Microwave and Optical Technology,

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4. John P. Gianvittorio and Yahya Rahmat-Samii, Fractal Antennas: A Novel

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16. Wireless. http://en.wikipedia.org/wiki/Wireless

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