turnstile fractal patch antenna report
DESCRIPTION
Turnstile Fractal Patch Antenna ReportTRANSCRIPT
A Project Report
on
DESIGN AND ANALYSIS OF TURNSTILE FRACTAL PATCH ANTENNA
Session 2011-2012
Submitted for partial fulfilment of award of the degree of
Bachelor of Technology
in
Electronics and Communication Engineering
from
Galgotias College of Engineering and Technology
Knowledge Park II, Greater Noida
By: Under the Supervision of:
Shailesh Kumar Patel (2909731009) Mr. Mukh Ram Rajbhar
Ravindra Singh (0809731069) Assistant professor
Shashibhushan Sharma (0809731075) ECE Dept. GCET
Yogendra Kumar (2909731012)
Certificate
This is to certify that Shailesh Kumar Patel, Ravindra Singh, Shashibhushan Sharma,
Yogendra Kumar have carried out this project titled Design and Analysis of Turnstile Fractal
Patch antenna, for the award of degree in Bachelor of Technology from Gautam Buddha
Technical university (formerly Uttar Pradesh technical University), Lucknow; under my
supervision. The project report embodies result of original work and studies carried out by
the students themselves.
Project Guide:
Dr. Manish Rai Mr. Mukh Ram Rajbhar
Head of the Department Assitant Professor
Dept. of ECE, GCET Dept. of ECE, GCET
Acknowledgement
We wish to express our deep sense of gratitude to Mukh Ram Sir, our project guide, for his
valuable guidance at all the stages of our project. His able guidance, constructive criticism
and his approach to the problems and the results obtained during the course of this project
helped us to a great extent in bringing this project to its completion.
We are grateful to Mukh Ram Sir, for his encouragement and succour with the resources
which helped in accomplishment of the project.
Shailesh Kumar Patel (2909731009)
Ravindra Singh (0809731069)
Shashibhushan Sharma (0809731075)
Yogendra Kumar (2909731012)
Abstract
In the undertaken project, we tried to design, simulate and fabricate turnstile fractal patch
antenna (TFPA) using Ansoft’s HFSS software and tried to include all the advantages of
MPA and as well as fractal structures like small size ,low volume, conformal mapping, easy
to integrate with host surfaces , self similarity and multiband properties with turnstile
antenna.
The above written objetives has been accomplished by designing the said TFPA for various
degrees and orientations of iterations, providing different changes in area and perimeter.
Hence, formulating the basic scheme for the effects on antenna pattern (port reflection
coefficient, radiation pattern etc) due to the variations in area and perimeter.
Table of Contents
Chapter -1
1.1 Introduction.
1.2 Antenna Terminology.
1.2.1 Radiation Pattern.
1.2.2 Isotropic ,Directional and Omni directional Pattern.
1.2.3 Radiation Power Density.
1.2.4 Antenna Beam width.
1.2.5 Antenna Directivity.
1.2.6 Antenna Efficiency.
1.2.7 Antenna Gain.
1.2.8 Bandwidth.
1.2.9 Polarisation.
1.2.9.1 Linear Polarisation.
1.2.9.2 Circular Polarisation.
1.2.9.3 Elliptical Polarisation.
1.2.10 Antenna Radiation Efficiency.
1.2.11 Relation Between Directivity and Effective Area.
Chapter - 2
Microstrip patch antenna
2.1 Microstrip antenna.
2.2 Feed Methods.
2.2.1. Microstrip line feed.
2.2.2. Coaxial Probe Feed.
2.3.1 Advantages and Drawb.
Chapter – 3
Fractal Geometry and Fractal Antenna
3.1. Fractal antenna.
3.2.Koch snowflake .
3.3.Construction of Koch snow flake
3.4. Representation of lindenmayer system
3.4.1.Sierpinski triangle
3.5. construction of sierpinski triangle
3.6 .Iterated structures
3.7.Natan Cohen criterion.
3.8. Log-periodic Antenna and Fractal.
3.9. Fractal Antenna Elements and Performance.
3.10. Fractal Antenna, Frequency invariance and Maxwell equations.
3.11. Antenna Tuning Unit.
3.12. Advantages and Drawbacks.
3.13 Disadvantages
3.14. Applications.
Chapter - 4
Basics of Turnstile Antenna
4.1.Turnstile Antenna.
Chapter - 5
Proposed Project
5.1. Introduction.
5.1.1. Objectives.
5.1.2. Tools.
5.1.3. Methodology.
5.1.4. Observations.
5.1.5. Design Formulas.
5.1.6. Design Parameters and Dimensions.
5.2. Feed Type.
5.3.1. Turnstile Fractal Patch Antenna (Zero Iteration).
5.3.1.1. Reflection Coefficient.
5.3.3. Turnstile Fractal Patch Antenna (Second Iteration).
5.3.3.1. Reflection Coefficient.
5.4. Observations and Graph.
5.5. Turnstile Fractal Patch Antenna.
Chapter - 6
Results and Conclusions
6.1. Results.
6.2. Conclusions.
6.2.1. Analysis of the Normalised Turnstile Fractal Patch Antenna.
6.3. Appendix.
6.4.future scope
6.5. References
List of Figure.
Chapter 1
1.1. Antenna as a transmission device showing constructive interference in
between the transmission line and finally release into the open media.
1.2Radiation Pattern shown in antenna coordinates.
1.3 Radiation Pattern, showing all the components.
1.3.1 First-null beam width (FNBW/2), which is usually used to approximate
the half-power beam width (HPBW).
1.4 (a) Antenna with input and output terminals.
1.4 (b) Reflection, conduction and dielectric losses
Chapter 2
2.1 Image showing Microstrip patch antenna.
2.2 Micro strip Feed Line.
2.3 Equivalent Circuit of Microstrip patch Feed.
2.4 Micro strip feed.
2.5 Coax Probe Feed.
Chapter -3
3.1 Fractals in nature.
3.2 The first four iteration of the Koch snowflake.
3.3 Sierpinski triangle in logic:
The first 16 conjunctions of lexicographically ordered arguments
3.4.1 Different triangular fractal iteration designs.
3.4.2 Different square fractal iteration designs.
Chapter -4
4.1 Turnstile antenna.
4.2 Two dipole turnstile antenna.
Chapter-5
5.1.Zero iteration turnstile patch antenna
5. 2 .Reflection coff. of zero itration.
5.3 2D radiation pattern of zero iteration at 0 phase
5.4 2D radiation pattern at 90 phase
5.5 Reflection coffcient of first iteration
5.6. 2D radiation pattern of first iteration at 0 phase
5.7. 2D radiation pattern of first iteration at 90 phase
5.8. Second iteration turnstile patch antenna.
5.9. Reflection coff. Of second itration.
5.10. Far Field 2 D Radiation pattern of second iteration TFPA at frequencies
5.11 Far Field 2 D Radiation pattern of second iteration TFPA at frequencies
5.12 Far Field 3- D Radiation pattern of second iteration TFPA
5.13 Far Field 3- D Radiation pattern of second iteration TFPA at frequencies
Chapter- 1
Introduction to Antenna and Antenna Terminology
1.1. Introduction
An antenna is defined by Webster’s Dictionary as ―usually a metallic device for radiating or
receiving radio waves‖. The IEEE Standards Definitions define antenna (or aerial) as ―a
means for radiating or receiving radio waves‖. In other words the antenna is the transitional
structure between free space and a guiding device.
Fig.1.1 Antenna as a transmission device showing constructive interference in between the
transmission line and finally release into the open media.
In addition to receiving or transmitting energy, an antenna (in an advance wireless system) is
usually required to optimise or accentuate the radiation energy in some directions and
suppress it in others. Thus the antenna must also serve as a directional device in addition to a
probing device. It must then take various forms to meet the particular need at hand.
The field of antenna is vigorous and dynamic, and over the last 50 years, antenna technology
has been an indispensable partner of the communication revolution. Many major advances
that occurred during this period are in common use today. However many more issues are
facing us today, especially since the demands for the system performance is even greater.
Hence antenna development and testing is of great interest to the engineering community of
the day.
1.2.Antenna Terminology
To describe the performance of an antenna, definitions of various parameters are necessary.
Some of the parameters are interrelated and not all of them need be specified for complete
description of the antenna performance.
1.2.1. Radiation Pattern
An antenna radiation pattern or antenna pattern is defined as ―a mathematical function or a
graphical representation of the radiation properties of the antenna as a function of space
coordinates. In most cases, the radiation pattern is determined in the far-field region and is
represented as a function of the
directional coordinates.
Radiation properties include
power flux density, radiation
intensity, field strength,
directivity, phase, or
polarization‖. The radiation
property of most concern is the
two- or three-dimensional
spatial distribution of radiated
energy as a function of the
observer’s position along a path
or surface of constant radius. A convenient set of coordinates is shown in Figure 1.2. A trace
of the received electric (magnetic) field at a constant radius is called the amplitude field
pattern. On the other hand, a graph of the spatial variation of the power density along a
constant radius is called an amplitude power pattern. Often the field and power patterns are
normalized with respect to their maximum value, yielding normalized field and power
patterns. Also, the power pattern is usually plotted on a logarithmic scale or more commonly
in decibels (dB).
Various parts of a radiation pattern are referred to as lobes, which may be sub-classified into
major or main, minor, side, and back lobes. A radiation lobe is a ―portion of the radiation
pattern bounded by regions of relatively weak radiation intensity‖. Figure 1.3a demonstrates a
Fig 1.2 Radiation Pattern shown in antenna coordinates
symmetrical three-dimensional polar pattern with a number of radiation lobes. Some are of
greater radiation intensity than others,
but all are classified as lobes.
A major lobe (also called main beam) is
defined as ―the radiation lobe containing
the direction of maximum radiation‖. In
the figure, the major lobe is pointing in
the Θ =0 direction. In some antennas,
such as split-beam antennas, there exist
more than one major lobe.
A minor lobe is any lobe except a major
lobe. A side lobe is ―a radiation lobe in
any direction other than the intended lobe‖.
(Usually a side lobe is adjacent to the main lobe
and occupies the hemisphere in the direction of
the main beam.) A back lobe is ―a radiation lobe whose axis makes an angle of approximately
180◦ with respect to the beam of an antenna‖. Usually it refers to a minor lobe that occupies
the hemisphere in a direction opposite to that of the major (main) lobe. Minor lobes usually
represent radiation in undesired directions, and they should be minimized. Side lobes are
normally the largest of the minor lobes. The level of minor lobes is usually expressed as a
ratio of the power density in the lobe in question to that of the major lobe. This ratio is often
termed the side lobe ratio or side lobe level. Side lobe levels of −20 dB or smaller are usually
not desirable in many applications.
1.2.2. Isotropic, Directional, and Omni-directional Patterns
An isotropic radiator is defined as ―a hypothetical lossless antenna having equal radiation in
all directions‖. Although it is ideal and not physically realizable, it is often taken as a
reference for expressing the directive properties of actual antennas. A directional antenna is
one ―having the property of radiating or receiving electromagnetic waves more effectively in
some directions than in others. This term is usually applied to an antenna whose maximum
directivity is significantly greater than that of a half-wave dipole‖. Omni-directional antennas
radiate at a specific direction, with no side lobes what so ever. An omni-directional pattern is
then a special type of a directional pattern.
Fig 1.3 Radiation Pattern, showing all the components
1.2.3. Radiation Power Density
Electromagnetic waves are used to transport information through a wireless medium or a
guiding structure, from one point to the other. It is then natural to assume that power and
energy are associated with electromagnetic fields. The quantity used to describe the power
associated with an electromagnetic wave is the instantaneous Poynting vector defined as
W = E ×H
W = instantaneous Poynting vector (W/m2)
E = instantaneous electric-field intensity (V/m)
H = instantaneous magnetic-field intensity (A/m)
Note that script letters are used to denote instantaneous fields and quantities, while roman
letters are used to represent their complex counterparts. Since the Poynting vector is a power
density, the total power crossing a closed surface can be obtained by integrating the normal
component of the Poynting vector over the entire surface. In equation form
where
P = instantaneous total power (W)
n = unit vector normal to the surface
da = infinitesimal area of the closed surface (m2)
----------(1)
The time-average Poynting vector (average power density) can be written
The ½ factor appears in Eq. (1.5) because the E and H fields represent peak values, and it
should be omitted for RMS values. Based on the definition of Eq. (1.5), the average power
radiated by an antenna (radiated power) can be written
1.2.4. Antenna Beam width
Associated with the pattern of an antenna is a parameter designated as beam width. The beam
width of a pattern is defined as the angular separation between two identical points on
opposite sides of the pattern maximum. In an antenna pattern, there are a number of
beamwidths. One of the most widely used beamwidths is the half-power beam width
(HPBW), which is defined by IEEE as: ―In a plane containing the direction of the maximum
of a beam, the angle between the two directions in which the radiation intensity is one-half
value of the beam‖. Another important beam width is the angular separation between the first
nulls of the pattern, and it is referred to as the first-null beam width (FNBW). Both of the
HPBW and FNBW. Other beamwidths are those where the pattern is −10 dB from the
maximum, or any other value. However, in practice, the term beam width, with no other
identification, usually refers to the HPBW.
The beam width of an antenna is a very important figure-of-merit and often is used as a trade-
off between it and the side lobe level; that is, as the beam width decreases, the side lobe
increases and vice versa. In addition, the beam width of the antenna is also used to describe
the resolution capabilities of the antenna to distinguish between two adjacent radiating
sources or radar targets. The most common resolution criterion states that the resolution
capability of an antenna to distinguish between two sources is equal to half the
Fig 1.3 First-null beam width (FNBW/2), which is usually used to approximate the half-
power beam width (HPBW).
1.2.5. Directivity
In the 1983 version of the IEEE Standard Definitions of Terms for Antennas, there was a
substantive change in the definition of directivity, compared to the definition of the 1973
version. Basically the term directivity in the 1983 version has been used to replace the term
directive gain of the 1973 version. In the 1983 version the term directive gain has been
deprecated. According to the authors of the 1983 standards, ―this change brings this standard
in line with common usage among antenna engineers and with other international standards,
notably those of the International Electrotechnical Commission (IEC)‖. Therefore directivity
of an antenna is defined as ―the ratio of the radiation intensity in a given direction from the
antenna to the radiation intensity averaged over all directions. The average radiation intensity
is equal to the total power radiated by the antenna divided by 4π. If the direction is not
specified, the direction of maximum radiation intensity is implied‖. Stated more simply, the
directivity of a non isotropic source is equal to the ratio of its radiation intensity in a given
direction over that of an isotropic source. In mathematical form, it can be written –
If the direction is not specified, it implies the direction of maximum radiation intensity
(maximum directivity) expressed as –
Where,
D = directivity (dimensionless).
D0 = maximum directivity (dimensionless).
U = radiation intensity (W/unit solid angle).
Umax = maximum radiation intensity (W/unit solid angle).
U0 = radiation intensity of isotropic source (W/unit solid angle).
Prad = total radiated power (W).
The directivity of an isotropic source is unity since its power is radiated equally well in all
directions. For all other sources, the maximum directivity will always be greater than unity,
and it is a relative ―figure-of-merit‖ that gives an indication of the directional properties of
the antenna as compared with those of an isotropic source. The directivity can be smaller than
unity; in fact it can be equal to zero. The values of directivity will be equal to or greater than
zero and equal to or less than the maximum directivity (0≤D≤D0).
1.2.6.Antenna Efficiency
Associated with an antenna are a number of efficiencies that can be defined. The total
antenna efficiency e0 is used to take into account losses at the input terminals and within the
structure of the antenna. Such losses may be due, referring to figure,
I. Reflections because of the mismatch between the transmission line and the antenna
and
II. I 2R losses (conduction and dielectric).
Fig.1.4 (a) Antenna with input and output terminals
Fig.1.4 (b) Reflection, conduction and dielectric losses
In general, the overall efficiency can be written
Where,
e0 = total efficiency (dimensionless)
err = reflection (mismatch) efficiency=(1−|_|2) (dimensionless)
ec = conduction efficiency (dimensionless)
ed = dielectric efficiency (dimensionless)
= voltage reflection coefficient at the input terminals of the antenna
Usually ec and ed are very difficult to compute, but they can be determined experimentally.
Even by measurements they cannot be separated, and it is usually more convenient to write as
–
where ecd =eced =antenna radiation efficiency, which is used to relate the gain and directivity.
1.2.7. Antenna Gain
Another useful measure describing the performance of an antenna is the gain. Although the
gain of the antenna is closely related to the directivity, it is a measure that takes into account
the efficiency of the antenna as well as its directional capabilities.Gain of an antenna (in a
given direction) is defined as ―the ratio of the intensity, in a given direction, to the radiation
intensity that would be obtained if the power accepted by the antenna were radiated
isotropically. The radiation intensity corresponding to the isotropically radiated power is
equal to the power accepted (input) by the antenna divided by 4π‖. In most cases we deal
with relative gain, which is defined as ―the ratio of the power gain in a given direction to the
power gain of a reference antenna in its referenced direction‖. The power input must be the
same for both antennas. The reference antenna is usually a dipole, horn, or any other antenna
whose gain can be calculated or it is known. In most cases, however, the reference antenna is
a lossless isotropic source.
Thus
When the direction is not stated, the power gain is usually taken in the direction of maximum
radiation.We can write that the total radiated power (Prad) is related to the total input power
(Pin) by –
where ecd is the antenna radiation efficiency (dimensionless). Here we define two gains:
1. gain (G), and the other,
2. absolute gain (Gabs), that also takes into account the reflection/mismatch losses.
Thus we can introduce an absolute gain Gabs that takes into account the reflection/mismatch
losses (due to the connection of the antenna element to the transmission line), and it can be
written as –
The maximum absolute gain G(0)abs is related to the maximum directivity D(0) by –
If the antenna is matched to the transmission line, that is, the antenna input impedance Z in is
equal to the characteristic impedance Z 0 of the line, then the two gains are equal, i.e. Gabs
=G.
Usually the gain is given in terms of decibels instead of the dimensionless quantity. The
conversion formula is given by -
1.2.8. Bandwidth
The bandwidth of an antenna is defined as ―the range of frequencies within which the
performance of the antenna, with respect to some characteristic, conforms to a specified
standard‖. The bandwidth can be considered to be the range of frequencies, on either side of a
centre frequency (usually the resonance frequency for a dipole), where the antenna
characteristics (such as input impedance, pattern, beam width, polarization, side lobe level,
gain, beam direction, radiation efficiency) are within an acceptable value of those at the
centre frequency. For broadband antennas, the bandwidth is usually expressed as the ratio of
the upper-to-lower frequencies of acceptable operation. For example, a 10:1 bandwidth
indicates that the upper frequency is 10 times greater than the lower. For narrowband
antennas, the bandwidth is expressed as a percentage of the frequency difference (upper
minus lower) over the centre frequency of the bandwidth. For example, a 5% bandwidth
indicates that the frequency difference of acceptable operation is 5% of the centre frequency
of the bandwidth.
Because the characteristics (input impedance, pattern, gain, polarization, etc.) of an antenna
do not necessarily vary in the same manner or are not even critically affected by the
frequency, there is no unique characterization of the bandwidth. The specifications are set in
each case to meet the needs of the particular application. Usually there is a distinction made
between pattern and input impedance variations. Accordingly pattern bandwidth and
impedance bandwidth are used to emphasize this distinction. Associated with pattern
bandwidth are gain, side lobe level, beam width, polarization, and beam direction while input
impedance and radiation efficiency are related to impedance bandwidth. For example, the
pattern of a linear dipole with overall length less than a half-wavelength is insensitive to
frequency. The limiting factor for this antenna is its impedance, and its bandwidth can be
formulated in terms of the Q. The Q of antennas or arrays with dimensions large compared to
the wavelength, excluding super directive designs, is near unity. Therefore the bandwidth is
usually formulated in terms of beam width, side lobe level, and pattern characteristics. For
intermediate length antennas, the bandwidth may be limited by either pattern or impedance
variations, depending on the particular application.
1.2.9. Polarisation
Polarization of an antenna in a given direction is defined as ―the polarization of the wave
transmitted (radiated) by the antenna. When the direction is not stated, the polarization is
taken to be the polarization in the direction of maximum gain‖. In practice, polarization of the
radiated energy varies with the direction from the centre of the antenna, so that different parts
of the pattern may have different polarizations.
Polarization of a radiated wave is defined as ―that property of an electromagnetic wave
describing the time-varying direction and relative magnitude of the electric-field vector;
specifically, the figure traced as a function of time by the extremity of the vector at a fixed
location in space, and the sense in which it is traced, as observed along the direction of
propagation‖. Polarization then is the curve traced by the end point of the arrow (vector)
representing the instantaneous electric field.
1.2.9. Linear, Circular, and Elliptical Polarizations
Polarization may be classified as linear, circular, or elliptical briefly they can be described as,
1.2.9.1. Linear Polarization - A time-harmonic wave is linearly polarized at a given point in
space if the electric-field (or magnetic-field) vector at that point is always oriented along the
same straight line at every instant of time. This is accomplished if the field vector (electric or
magnetic) possesses the following:
I. Only one component, or
II. Two orthogonal linear components that are in time phase or 180◦ (or multiples
of180◦) out-of-phase.
1.2.9.2. Circular Polarization - A time-harmonic wave is circularly polarized at a given
point in space if the electric (or magnetic) field vector at that point traces a circle as a
function of time. The necessary and sufficient conditions to accomplish this are if the
field vector (electric or magnetic) possesses all of the following:
I. The field must have two orthogonal linear components, and
II. The two components must have the same magnitude, and
III. The two components must have a time-phase difference of odd multiples of
900.
The sense of rotation is always determined by rotating the phase-leading component
toward the phase-lagging component and observing the field rotation as the wave is
viewed as it travels away from the observer. If the rotation is clockwise, the wave is
right-hand (or clockwise) circularly polarized; if the rotation is counter clockwise, the
wave is left-hand (or counter clockwise) circularly polarized. The rotation of the
phase-leading component toward the phase-lagging component should be done along
the angular separation between the two components that is less than 1800. Phases
equal to or greater than 00 and less than 180
0 should be considered leading whereas
those equal to or greater than 180degree and less than 3600 should be considered
lagging.
1.2.9.3. Elliptical Polarization - A time-harmonic wave is elliptically polarized if the
tip of the field vector (electric or magnetic) traces an elliptical locus in space. At
various instants of time the field vector changes continuously with time in such a
manner as to describe an elliptical locus. It is right-hand (clockwise) elliptically
polarized if the field vector rotates clockwise, and it is left-hand (counter
clockwise) elliptically polarized if the field vector of the ellipse rotates counter
clockwise. The sense of rotation is determined using the same rules as for the
circular polarization. In addition to the sense of rotation, elliptically polarized
waves are also specified by their axial ratio whose magnitude is the ratio of the
major to the minor axis.
A wave is elliptically polarized if it is not linearly or circularly polarized. Although linear
and circular polarizations are special cases of elliptical, usually in practice elliptical
polarization refers to other than linear or circular. The necessary and sufficient conditions
to accomplish this are if the field vector (electric or magnetic) possesses all of the
following:
I. The field must have two orthogonal linear components, and
II. The two components can be of the same or different magnitude.
III. (a) If the two components are not of the same magnitude, the time-phase difference
between the two components must not be 00 or multiples of 180
0 (because it will then
be linear). (b) If the two components are of the same magnitude, the time-phase
difference between the two components must not be odd multiples of 900 (because it
will then be circular).
1.2.10. Antenna Radiation Efficiency
The antenna efficiency that takes into account the reflection, conduction, and dielectric
losses. The conduction and dielectric losses of an antenna are very difficult to compute and in
most cases they are measured. Even with measurements, they are difficult to separate and
they are usually lumped together to form the ecd efficiency. The resistance RL is used to
represent the conduction–dielectric losses. The conduction–dielectric efficiency ecd is defined
as the ratio of the power delivered to the radiation resistance Rr to the power delivered to Rr
and RL.
The radiation efficiency can be written
For a metal rod of length l and uniform cross-sectional area A, the dc resistance is given by-
1.2.11. Relation between Directivity and Effective Area
In general then, the maximum effective area (Aem ) of any antenna is related to its maximum
directivity (D0) by –
Thus this equation is multiplied by the power density of the incident wave it leads to the
maximum power that can be delivered to the load. This assumes that there are no conduction-
dielectric losses (radiation efficiency ecd is unity), the antenna is matched to the load
(reflection efficiency er is unity), and the polarization of the impinging wave matches that of
the antenna (polarization loss factor PLF and polarization efficiency pe are unity). If there are
losses associated with an antenna, its maximum effective aperture above equation must be
modified to account for conduction-dielectric losses (radiation efficiency). Thus
CHAPTER -2
Microstrip Patch Antenna
2.1. Microstrip Antenna
Microstrip antenna, consist of a very thin (t << 0, where 0 is the free space wavelength)
metallic strip (patch) placed a small fraction of a wavelength (h << 0 , usually 0.003 0 ≤ h ≤
0.05 0) above a ground plane. The microstrip patch is designed so its pattern maximum is
normal to the patch (broadside radiator). This is accomplished by properly choosing the mode
of excitation beneath the patch. For the rectangular patch the length L of the element is
usually 0 /3< L < 0 /2. The strip and the ground are separated by a dielectric sheet. There
are numerous substrate that can be used to design microstrip antennas, and their dielectric
constant are usually in the range 2.2 . The ones that are most often used are thick
substrates whose dielectric constant is in the lower end the range because they provide better
efficiency, larger bandwidth, loosely bound field for radiation; but do all this at the expense
of larger element size. Thin substrate with higher dielectric constant are desirable for
microwave circuitry because ther require tightly bound fields to minimise undesirable
radiation and coupling, and lead to smaller element size.
2.2.Feed Methods
There are many configurations that can be used to feed the microstrip match antenna. The
four most popular are –
2.2.1.Microstrip Line feed – is easy to fabricate, usually is much smaller as compared to
the patch. However as the substrate thickness increases, surface waves and spurious feed
radiation increases, which for practical design limits the bandwidth.
Fig2.2 Microstrip Feed Line Fig 2.3 Equivalent Circuit of Microstrip Feed
Variation in Microstrip feed can be provided by having more than one feeds
This may lead to orthogonal polarisation, if the 2 feeds are in phase, otherwise if they
are 900 apart, circular polarisation may take place.
2.2.2Coaxial Probe feed – the inner conductor of the coax is attached to the Radiating
patch while the outer conductor is connected to the ground plane. It is also easy to
fabricate and match, and has low spurious radiation. However, it has narrow bandwidth
and is more difficult to model if the substrate is thick.
Fig 2.4 microstrip feed
Fig 2.5 Coax Probe Feed fig 2.6 Equivalent circuit of Coax
Probe Feed
2.3.Advantages and Drawbacks
2.3.1.Advantages:
1. The extremely low profile of the microstrip antenna makes it lightweight and it
occupies very little volume of the structure or vehicle on which it is mounted.
2. The patch element or an array of patch elements, when produced in large quantities,
can be fabricated with a simple etching process, which can lead to greatly reduced
fabrication cost.
3. Multiple-frequency operation is possible by using either stacked patches or a patch
with loaded pin or a stub.
4. There are other miscellaneous advantages, such as the low antenna radar cross section
(RCS), and the microstrip antenna technology can be combined with the reflectarray
technology to achieve very large aperture without any complex and RF lossy
beamformer.
Besides no of advantages MSPA has following drawbacks also.
1. A single-patch microstrip antenna with a thin substrate (thickness < 0.02 of freq)
generally has a narrow bandwidth of less than 5%.
2. The microstrip antenna can handle relatively lower RF power due to the small
separation between the radiating patch and its ground plane. Depending on the
substrate thickness, metal edge sharpness, and the frequency of operation, a few
kilowatts of peak power for microstrip lines at X-band have been reported.
3. The microstrip array generally has a larger ohmic insertion loss than other types of
antennas of equivalent aperture size. This ohmic loss mostly occurs in the dielectric
substrate and the metal conductor of the microstrip line power dividing circuit.
4. Patch antennas have quite a few benefits, including the aforementioned inexpensive
price, versatility, and ease of manufacture. The low profile nature of patch antennas is
also obvious as well as the small size needed to generate a sizeable directive gain.
5. Patch antennas however do have some disadvantages. Primarily; narrow bandwidth
and poor efficiency are top issues that plague microstrip antenna designers. It is
common to require multiple patch antennas to cover different frequency bands due to
their narrow bandwidth.
6. This disadvantage is being somewhat mitigated by the fact that many communications
protocols are moving towards CDMA and TDMA techniques which uses a single
band. The poor efficiency of patch antennas is also a particular disadvantage in
favored applications like cell phones and space hardware due to the limited power
resources in these cases.
7. Small applications which benefit greatly from the compact size of patch antennas also
seek efficient systems which allow for longer battery life in mobile applications. The
efficiency of patch antennas can be increased by utilizing materials with lower
dielectric constants for the substrate, as well as moving the antenna farther away
from the ground plane (ex. utilizing a thicker substrate). These methods change the
frequency characteristics and gain patterns of the antennas while also creating
challenges in design.
8. Another disadvantage of patch antennas is the complex nature of performing analyses
to determine gain patterns. While simple patch antennas (squares and circles) are
relatively easy to analyze, complex structures often become necessary to improve
gain, pattern, bandwidth or efficiency.
9. These complex patterns are non-trivial to analyze and thus are often modeled utilizing
the FDTD method which can handle more complex structures with much more
facility. It is the goal of this project to provide an introduction to this methodology.
CHAPTER-3
Fractal Geometry and Fractal Antenna
3.1.Fractal Antenna
Derived from Latin word ―fractus‖ meaning broken. A fractal is ―a rough or
fragmented geometric shape that can be split into parts, each of which is (at least
approximately) a reduced-size copy of the whole,‖ a property called self-similarity. Even
shapes which are not self-similar can be fractals. The most famous of these is the Koch
Snowflake.
Fig 3.1 Fractals in nature.
3.2.Koch Snowflake
Fig 3.2 The first four iterations of the Koch snowflake.
The Koch snowflake (also known as the Koch star and Koch island) is a mathematical curve
and one of the earliest fractal curves to have been described. It is based on the Koch curve,
which appeared in a 1904 paper titled "On a continuous curve without tangents, construct
able from elementary geometry" (original French title: "Sur une courbe continue sans
tangente, obtenue par une construction géométrique élémentaire") by the Swedish
mathematician Helge von Koch.
3.3.Construction of Koch snowflake – The Koch snowflake can be constructed by starting
with an equilateral triangle, then recursively altering each line segment as follows:
1. Divide the line segment into three segments of equal length.
2. Draw an equilateral triangle that has the middle segment from step 1 as its base and
points outward.
3. Remove the line segment that is the base of the triangle from step 2.
After one iteration of this process, the result is a shape similar to the Star of David.The Koch
snowflake is the limit approached as the above steps are followed over and over again. The
Koch curve originally described by Koch is constructed with only one of the three sides of
the original triangle. In other words, three Koch curves make a Koch snowflake.
Properties – The Koch curve has an infinite length because each time the steps above are
performed on each line segment of the figure there are four times as many line segments, the
length of each being one-third the length of the segments in the previous stage. Hence the
total length increases by one third and thus the length at step n will be (4/3)n of the original
triangle perimeter: the fractal dimension is log 4/log 3 ≈ 1.26, greater than the dimension of a
line (1) but less than Peano's space-filling curve . The Koch curve is continuous everywhere
but differentiable nowhere.
wheretaking s as the side length.
The side length of each successive small triangle is 1/3 of those in the previous iteration;
because the area of the added triangles is proportional to the square of its side length, the area
of each triangle added in the nth step is 1/9 of that in the (n-1)th step. In each iteration after
the first, 4 times as many triangles are added as in the previous iteration; because the first
iteration adds 3 triangles, the nth iteration will add triangles. Combining these two
formulae gives the iteration formula:
where A0 is area of the original triangle. Substituting in
and expanding yields:
In the limit, as n goes to infinity, the limit of the sum of the powers of 4/9 is 4/5, so
So the area of a Koch snowflake is 8/5 of the area of the original triangle, or Therefore
the infinite perimeter of the Koch triangle encloses a finite area.
3.4.Representation as Lindenmayer system
The Koch Curve can be expressed by a rewrite system (Lindenmayer system).
Alphabet : F
Constants : +, −
Axiom : F++F++F
Production rules: F → F−F++F−F
Here, F means "draw forward", + means "turn right 60°", and − means "turn left 60°"
3.4.1.Sierpinski triangle
Fig 3.3 Sierpinski triangle in logic:
The first 16 conjunctions of lexicographically ordered arguments
The Sierpinski triangle (also with the original orthography Sierpiński), also called the
Sierpinski gasket or the Sierpinski Sieve, is a fractal and attractive fixed set named after the
Polish mathematician Wacław Sierpiński who described it in 1915. However, similar patterns
appear already in the 13th-century Cosmati mosaics in the cathedral of Anagni, Italy.
Originally constructed as a curve, this is one of the basic examples of self-similar sets, i.e. it
is a mathematically generated pattern that can be reproducible at any magnification or
reduction.Comparing the Sierpinski triangle or the Sierpinski carpet to equivalent repetitive
tiling arrangements, it is evident that similar structures can be built into any rep- tile
arrangements.
3.5. Construction Sierpinski triangle
An algorithm for obtaining arbitrarily close approximations to the Sierpinski triangle is as
follows:
Note: each removed triangle (a trema) is topologically an open set.
Fig 3.4 different triangular fractal iteration designs
1. Start with any triangle in a plane (any closed, bounded region in the plane will
actually work). The canonical Sierpinski triangle uses an equilateral triangle with a
base parallel to the horizontal axis (first image).
2. Shrink the triangle to ½ height and ½ width, make three copies, and position the three
shrunken triangles so that each triangle touches the two other triangles at a corner
(image 2). Note the emergence of the central hole - because the three shrunken
triangles can between them cover only 3/4 of the area of the original. (Holes are an
important feature of Sierpinski's triangle.)
3. Repeat step 2 with each of the smaller triangles (image 3 and so on).
Note that this infinite process is not dependent upon the starting shape being a triangle—it is
just clearer that way. The first few steps starting, for example, from a square also tend
towards a Sierpinski triangle. Michael Barnsley used an image of a fish to illustrate this in his
paper "V-variable fractals and superfractals.
Fig 3.4 different square fractal iteration designs
The actual fractal is what would be obtained after an infinite number of iterations. More
formally, one describes it in terms of functions on closed sets of points. If we let da note the
dilation by a factor of ½ about a point a, then the Sierpinski triangle with corners a, b, and c is
the fixed set of the transformation da U db U dc.
This is an attrctive fixed set, so that when the operation is applied to any other set repeatedly,
the images converge on the Sierpinski triangle. This is what is happening with the triangle
above, but any other set would suffice.If one takes a point and applies each of the
transformations da, db, and dc to it randomly, the resulting points will be dense in the
Sierpinski triangle, so the following algorithm will again generate arbitrarily close
approximations to it:
Start by labeling p1, p2 and p3 as the corners of the Sierpinski triangle, and a random point v1.
Set vn+1 = ½ ( vn + prn ), where rn is a random number 1, 2 or 3. Draw the points v1 to v∞. If
the first point v1 was a point on the Sierpiński triangle, then all the points vn lie on the
Sierpinski triangle. If the first point v1 to lie within the perimeter of the triangle is not a point
on the Sierpinski triangle, none of the points vn will lie on the Sierpinski triangle, however
they will converge on the triangle. If v1 is outside the triangle, the only way vn will land on
the actual triangle, is if vn is on what would be part of the triangle, if the triangle was
infinitely large
3.5.1.Iterated structure :
1. Take 3 points in a plane to form a triangle, you
need not draw it.
2. Randomly select any point inside the triangle and
consider that your current position.
3. Randomly select any one of the 3 vertex points.
4. Move half the distance from your current position
to the selected vertex.
5. Plot the current position.
6. Repeat from step 3.
Note: This method is also called the Chaos game. You can start from any point outside or
inside the triangle, and it would eventually form the Sierpinski Gasket with a few leftover
points. It is interesting to do this with pencil and paper. A brief outline is formed after placing
approximately one hundred points, and detail begins to appear after a few hundred.
3.6. Fractal antenna
An example of a fractal antenna: a space-filling curve called a Minkowski IslandA fractal
antenna is an antenna that uses a fractal, self-similar design to maximize the length, or
increase the perimeter (on inside sections or the outer structure), of material that can receive
or transmit electromagnetic radiation within a given total surface area or volume.
Such fractal antennas are also referred to as multilevel and space filling curves, but the key
aspect lies in their repetition of a motif over two or more scale sizes or "iterations". For this
reason, fractal antennas are very compact, are multiband or wideband, and have useful
applications in cellular telephone and microwave communications.
A fractal antenna's response differs markedly from traditional antenna designs, in that it is
capable of operating with good-to-excellent performance at many different frequencies
simultaneously. Normally standard antennas have to be "cut" for the frequency for which
they are to be used—and thus the standard antennas only work well at that frequency. This
makes the fractal antenna an excellent design for wideband and multiband applications.
3.7.Nathan Cohen Criterion –
In 1995, in a paper Nathan Cohen wrote -
In order for an antenna to work equally well at all frequencies, it must satisfy two criteria:
1. it must be symmetrical about a point,
2. and it must be self-similar, having the same basic appearance at every scale: that is, it
has to be fractal.
3.8.Log periodic antennas and fractals
The first fractal "antennas" were, in fact, fractal "arrays", with fractal arrangements of
antenna elements, and not recognized initially as having self-similarity as their attribute. Log-
periodic antennas are arrays, around since the 1950s (invented by Isbell and DuHamel), that
are such fractal arrays. They are a common form used in TV antennas, and are arrow-head in
shape.
3.9.Fractal antennas element and performance
Antenna elements (as opposed to antenna arrays) made from self-similar shapes were first
created by Nathan Cohen, then a professor at Boston University, starting in 1988. Cohen's
efforts with a variety of fractal antenna designs were first published in 1995 (thus the first
scientific publication on fractal antennas), and a number of patents have been issued from the
1995 filing priority of invention (see list in references, for example). Most allusions to fractal
antennas make reference to these "fractal element antennas".
Many fractal element antennas use the fractal structure as a virtual combination of capacitors
and inductors. This makes the antenna so that it has many different resonances which can be
chosen and adjusted by choosing the proper fractal design. Electrical resonances may not be
directly related to a particular scale size of the fractal antenna structure. The physical size of
the antenna is unrelated to its resonant or broadband performance. The general rule of
antenna length being near target frequency wavelength does not apply itself in the same way
with fractal antennas.This complexity arises because the current on the structure has a
complex arrangement caused by the inductance and self capacitance. In general, although
their effective electrical length is longer, the fractal element antennas are themselves
physically smaller.
Fractal element antennas are shrunken compared to conventional designs, and do not need
additional components. In general the fractal dimension of a fractal antenna is a poor
predictor of its performance and application. Not all fractal antennas work well for a given
application or set of applications. Computer search methods and antenna simulations are
commonly used to identify which fractal antenna designs best meet the need of the
application.Although the first validation of the technology was published as early as 1995,
recent independent studies show advantages of the fractal element technology in real-life
applications, such as RFID and cell phone.
3.10.Fractal antennas, frequency invariance, and Maxwell's equations
A different and also useful attribute of some fractal element antennas is their self-scaling
aspect. In 1999, it was discovered that self-similarity was one of the underlying requirements
to make antennas "invariant" (same radiation properties) at a number or range of frequencies.
Previously, under Rumsey's Principle, it was believed that antennas had to be defined by
angles for this to be true; the 1999 analysis, based on Maxwell's equations, showed this to be
a subset of the more general set of self-similar conditions.
Hence fractal antennas offer a closed-form and unique insight into a key aspect of
electromagnetic phenomena. To wit: the invariance property of Maxwell's equations: this
property being in keeping with the fundamental nature of Maxwell’s derivation and
mathematical treatment of electromagnetic phenomena, and is further demonstrated by its
complete harmony and integration with Einstein’s special theory of relativity.
3.11.Antenna tuning units
Antenna tuning units are typically not required on fractal antennas due to their wide
bandwidth and complex resonance. However, if a transmitting antenna has deep nulls in its
response or has electromagnetic structural issues that require equalization then an antenna
tuning unit should be used, per the definition of required.
3.12.Advantages
1. Fractal element antennas are shrunken compared to conventional designs, and do not
need additional components.
2. Reduced Dimension and better utilisation of space.
3. In many cases, the use of fractal element antennas can simplify circuit design, reduce
construction costs and improve reliability.
3.13.Disadvantages -
1. Not all fractal antennas work well for a given application or set of applications.
2. In general the fractal dimension of a fractal antenna is a poor predictor of its
performance and application.
3.14.Applications
Fractal antennas can be used for a wide variety of applications. For example,-
1. Fractal antennas can be used in cellular phones to provide a much better reception
than that provided by other types of antennas that are only capable of operating on
one or a few frequencies.
2. Fractal antennas can also be used as filters for radio signals as well as loads, ground
planes, and counterpoises within antenna systems.
3. There seems to be an increased use of Fractal Antenna in Military communication.
3.15.Other applications
In addition to their use as antennas, fractals have also found application in other antenna
system components including loads, counterpoises, and ground planes. Fractal inductors and
fractal tuned circuits (fractal resonators) were also discovered and invented simultaneously
with fractal element antennas. An emerging example of such is in meta-materials.
A recent report demonstrates using close-packed fractal resonators to make the first
wideband meta-material invisibility cloak, at microwaves. Fractal filters (a type of tuned
circuit) are another example where the superiority of the approach has been proven.
As fractals can be used as counterpoises, loads, ground planes, and filters, all parts that can be
integrated with antennas, they are considered parts of some antenna systems and thus are
discussed in the context of fractal antennas.
CHAPTER-4
Basics of Turnstile Antenna
4.1.Turnstile Antenna
A turnstile antenna is a set of two dipole antennas aligned at right angles to each other and
fed 90 degrees out-of-phase.The name reflects that the antenna looks like a turnstile when
mounted horizontally . When mounted horizontally the antenna is nearly omnidirectional on
the horizontal plane. When mounted vertically the antenna is directional to a right angle to its
plane and is circularly polarized. The turnstile antenna is often used forcommunication
satellites because, being circularly polarized, the polarization of the signal doesn't rotate
when the satellite rotates.
The principles of the turnstile antenna are also applicable to Yagi and Log periodic antennas.
Fig 4.1 Turnstile antenna
Fig 4.2 Two dipole turnstile antenna
A Turnstile antenna consists of a pair of crossed dipoles PLUS a pair of reflector elements
spaced about quarter wavelength below (behind) the driven pair. Without the reflectors, the
pair of crossed dipoles are known simply as "crossed dipoles".
A Turnstile antenna is an excellent antenna for LEO, Polar orbit, satellites. Like all
antennas it should be installed "in the clear". I have used one for over a dozen years for
receiving the 137MHz weather satellite image signals. I start receiving image data within a
few seconds of the satellite crossing my AOS horizon and continue to receive image data
until a second or two after LOS! No one can ask for more than that. Here in New England, I
get image data from south of Cuba to North of Hudson Bay!
As noted above, the secret is to get the Turnstyle up above all local obsticles. Install
it as high as you can.
An even "better" omni-directional antenna for LEO satellite work is the Quadrifilar
Helix. This gives equal coverage to the Turnstyle and has the added advantage of maintaining
its circular polarisation property over the total hemi-sphere, from horizon to horizon in all
direction, and over all elevation angles.
The Turnstile, as noted above, is good. However it is only circular polarised at the
zenith (directly overhead). At the horizon it is linear, horizontal, polarised. It is elliptically
polarised, of varying ratios, at all intermediate elevation angles.
CHAPTER-5
Proposed Project
5.1.Introduction
5.1.1Objectives
1. To study the effect of fractal geometry (negation, addition, and normalised) of
Turnstile patch antenna.
2. To study the effect of change in perimeter and area of turnstile patch antenna
3. To construct a Turnstile fractal Patch antenna working at a frequency range of
3 to 10 GHz.
As specified above, the project to be explained within the next few sections aims at finding
effects of different fractal geometry on Turnstile fractal Patch antenna. In addition, the aim
was to find an iterative solution, which does not affect the antenna radiation pattern to a large
extent, but at the same time, make it more directive and wideband than the original one.
In the process, it was also observed that different geometry of fractals may introduce different
variations in
1. Area
2. Perimeter
This gives an additional dimension to the project, i.e. observing the effect of area and
perimeter variation on antenna’s frequency, directivity, and gain.
We would not say that we have been able to achieve all the goals we had kept in mind when
we commenced our work on the given project; but what so ever, the project has been a
success in at least one of the above written aims.
5.1.2.Tools
The basic equipment required was Ansoft HFSS (Refer to Appendix 1) and a PC that could
run it. The rest was just hardwork. In all it was a nice project and Mr. Mukhram Sir provided
with much needed support and motivation.
5.1.3.Methodology
The method can be divided into the following steps –
1. Construction of Turnstile Fractal Patch antenna based on calculations (Refer
Appendix 2).
2. Simulation and procurement of results based on the suitable condition (Refer
Appendix 2).
3. Formation of fractals of different kinds which included
a. 1st degree iteration.
b. 2nd
degree iteration.
4. Procure results for the above mentioned configuration.
5. Compare the graphs.
6. Reaching Conclusions.
5.1.4.Observations
Observations can be divided into 3 categories with regard to the 5 configurations of the patch
antenna –
a. Zero degree iteration or Original Antenna
b. First degree iteration antenna.
c. Second degree iteration antenna.
d. Normalised iteration of Final Antenna
The zero degree iteration is the antenna is the original Elliptical Patch Antenna which forms
the base of the rest of the antennas. The zero degree iterative antenna, forms the basis of
observation for rest of the antennas to which the characteristics of all the other antennas are
compared .The first degree additive iterative antenna, consists of right triangular fractals
which are added to the elliptical patch alternatively to the elliptical antenna segments as
shown. Segmentation is done in a way so that nearly equal in length, though for turnstile, it is
not possible to make the length exactly equal.
5.1.5.Design formula :
To get to know ADS( Advance Design System ) and get a feeling of what antenna design is
all about, we started of by designing a simple dipole antenna. We picked 2.1 GHz, just a
random frequency, to test the theoretical content. We are here using the RT/Duriod substrate
(see Appendix II for substrate parameters).
L = 0.44 = 0.44. = 63 mm
5.1.6.DESIGN PARAMETERS
Software Name Ansoft HFSS
Frequency 2.1 GHz
Substrate 72x72 mm2 ( RT / Duriod )
Height 3.2 mm
Dipole length 26.5 mm
Dipole width 12 mm
Feed type Coaxial
Center spacing 13mm
Zero Iteration Turnstile Fractal Patch Antenna(TFPA)
The Zero iterated TFPA has been designed and given in the fig5.1 . After simualting the
structure with with HFSS with feeding wave port we see that the TFPA resonates at three
frequencies . These frequences 3.656 GHz. The reflection coefficient at these frequency is -
19.882 dB fig 5.2
Afre setting the polar pattern at phi 0 and 90 deg . we found that the radiation pattern at these
three frequenciecs are almost the unidirectional . The radiation pattern at 3.656 GHz is
omnidirectional and more uniformas shown in the fig5.3 .
The two dimensional radiation patteran at phi 0 and 90 deg has been plot as given in the
fig.5.3 & 5.4. it may be due to feeding .or phse different different than 90 deg. Between two
feed point. After optimization this can be get that maximum radiation at theta at 0 deg.
Fig.5.1 Zero Iteration Turnstile Fractal Patch Antenna(TFPA)
Fig. 5.2 Reflection Cofficient (S11) of Zero iteration TFPA
Fig5.3. Far Field 2 D Radiation pattern of zero iteration TFPA at frequencies 3.656 GHz at
phi 0 deg.
Fig. 5.4 Far Field 2 D Radiation pattern of zero iteration TFPA at frequencies 3.655GHz at
phi 90 deg.
First Iteration Turnstile Fractal Patch Antenna(TFPA)
The first iterated TFPA has been generated from the zero iterated TFPA by substaceting a
rectanualr rectangle as shown in the fig 5.5 . After simualting the structure with HFSS with
feeding wave port we see that the TFPA resonates at two frequencies . These frequences
are3.7, & 9.505GHz respectively. The reflection coefficient at these frequencies are -17.59
&-22.038dB respectively as shown in fig 5.6
Afre setting the polar pattern at phi0 and 90 deg . we found that the radiation pattern at these
three frequenciecs are almost the unidirectional . The radiation pattern at the firat two
frequency are more directive that second one i.e. (at 3.7,and 9.505 GHz the pattern are more
directive ). The radiation pattern at the second frequency 9.505GHz is omnidirectional and
more uniformas shown in the fig5.7 .
The two dimensional radiation patteran at phi 0 and 90 deg has been plot as given in the
fig.5.6&5.7.
Fig.5.4 Second Iteration Turnstile Fractal Patch Antenna(TFPA)
Fig. 5.5 Reflection Cofficient (S11) of second iteration TFPA
Fig5.6. Far Field 2 D Radiation pattern of first iteration TFPA at frequencies 3.700 &
9.505GHz at phi 0 deg.
Fig. 5.7 Far Field 2 D Radiation pattern of first iteration TFPA at frequencies 3.70 &
9.505GHz at phi 90 deg.
Second Iteration Turnstile Fractal Patch Antenna(TFPA)
The second iterated TFPA has been generated from the first iterated TFPA by substaceting
a rectanualr rectangle as shown in the fig5.8 . After simualting the structure with with HFSS
with feeding wave port we see that the TFPA resonates at three frequencies . These
frequences are3.745,7.39 &9.505GHz respectively. The reflection coefficient at these
frequencies are -20.1073,-10.8172&-22.4544B respectively as shown in fig 5.9
Afre setting the polar pattern at phi0 and 90 deg . we found that the radiation pattern at these
three frequenciecs are almost the unidirectional . The radiation pattern at the firat two
frequency are more directive that third one i.e. (at 3.745,and 7.39 GHz the pattern are more
directive ). The radiation pattern at the third frequency 9.505GHz is omnidirectional and
more uniformas shown in the fig5.10 .
The two dimensional radiation patteran at phi 0 and 90 deg has been plot as given in the
fig.5.10&5.11. the three d radiation pattern is also given in the fig 5.12 to 5.13. from these fig
the conclusion si same as from the 2 dimensional radiation pattern .the maximum farfiled
electric field is about 10 Db attheta18 deg . it may be due to feeding .or phse different
different than 90 deg. Between two feed point. After optimization this can be get that
maximum radiation at theta at 0 deg.
Fig.5.8 Second Iteration Turnstile Fractal Patch Antenna(TFPA)
Fig. 5.9 Reflection Cofficient (S11) of second iteration TFPA
Fig5.10. Far Field 2 D Radiation pattern of second iteration TFPA at frequencies 3.745,7.39
&9.505GHz at phi 0 deg.
Fig. 5.11 Far Field 2 D Radiation pattern of second iteration TFPA at frequencies 3.745,7.39
&9.505GHz at phi 90 deg.
Fig.5.12 Far Field 3- D Radiation pattern of second iteration TFPA at frequency 3.745GHz.
Fig. 5.13 Far Field 3- D Radiation pattern of second iteration TFPA at frequencies 3.745,7.39
&9.505GHz at phi 90 deg.
Fig. 5.14 Far Field 2 D Radiation pattern of second iteration TFPA at frequencies 3.745,7.39
&9.505GHz at phi 90 deg.
Analysis from previous design:
No of Iterations No of Bands Frequency (GHz) Reflection coefficient
0 1 3.65 -19.88
1 2 3.70
9.50
-17.50
-22.03
2 3 3.74
7.39
9.50
-20.10
-10.51
-22.46
Observation and Graphs
I. Turnstile Fractal Patch Antenna.
The antenna consists of a 66 mm length turnstile patch with material RT duriod as substrate.
It is supposed to be made of copper. It is placed upon a Duroid (dielectric constant = 2.2)
Dielectric substrate, of height 3.2 mm, a copper ground plate is present beneath the substrate.
A 40 ohms and 20 ohms feed line is provided with the antenna which is connected to the both
Wave port respectively. The dimensions and related measurements have been explained in
Appendix 2 and Appendix 3.
When simulate the structure wath taking the frequency range 1 to 4 GHz, We get the
rectangular plot of frequency vs gain like this.
S parameter (Frequency v/s dB)
S parameter (Frequency v/s dB)
CHAPTER - 6
Results and Conclusions
6.1. Results :
We have Design and Simulate the turnstile fractal patch antenna, which is act as multiband
antenna when we create fractal structure using iterative mechanism of fractal geometry.
We got the following result :
No of Iterations No of Bands Frequency (GHz) Reflection coefficient
0 1 3.65 -19.88
1 2 3.70
9.50
-17.50
-22.03
2 3 3.74
7.39
9.50
-20.10
-10.51
-22.46
6.2. Conclusions :
1. fractal geometry increases the directivity of the antenna
2. Fractal geometry increases the wide band capacity of the antenna.
3. By keeping the area constant and increasing perimeter, one can achieve better
Directivity while keeping the frequency the same.
4. On increasing the perimeter, the wideband capacity of the antenna, and the directivity
of the antenna increases.
5. Fractal geometry increases Omni-directional characteristic of Turnstile Fractal Patch
Antenna.
6. No direct relation between antenna area and frequency or directivity was computable
from the experiments performed.
Analysis of the Normalised Tunstile Fractal Patch Antenna
1. The Normalised Fractal antenna retained the frequency of the Original antenna.
2. The Normalised antenna increased Directivity and Gain of the Original Antenna.
3. The Normalised fractal geometry increased the Omni-directional characteristic of the
Turnstile Fractal antenna.
4. Hence it can be used better for applications which require Omni-directional signals,
for example – Cellular Communication, Radar Communication.
6.3. Appendix
Construction on HFSS –
1. Patch – Patch needs to be calculated based on the given equation. It can be
constructed using various drawing tools on HFSS. Boundary condition of finite
conductivity is provided.
2. Dielectric Substrate – Constructed in form of Cube just below the Patch. It is then
given the properties of a suitable material (in our case duroid). Its length must be
taken into account.
3. Ground Plane – A sheet is provided beneath the dielectric substrate, it is provided
with the boundary condition of finite conductivity, based on property of a conductor
(we used Copper).
4. Feed – A strip of copper (dimensionally very small to the patch) is provided for EM
wave from wave port to patch. It must be of 50 ohm conductivity.
5. Wave port – Wave port is used to provide excitation to the whole model. Its length
must be at least /4.
6. Air Box – It is provided to restrict the area where the antenna must radiate. It must be
big enough but not very big to provide reflected interference. It is provided with
Radiation Boundary condition
7. Meshing – A Meshing length is provided to the air box which must be /10.
8. Far Field Set up – An infinite sphere far field condition is set up to calculate far field
parameter.
6.4. Future scope :
Turnstile antenna having many advantages over the other available antennas, like other
coventional antennas cannot work with high frequency. But the turnstile antenna can work
with high frequency. And turnstile antenna having the features of highly directional antenna.
So turnstile antenna having the very important use in coming future, these types of antenna
can be used in new emerging devices like Cellphone, tablet and others Personal devices like
GPS handheld etc.
6.5. Refrences
[1.] Antenna Theory – Basics and Design by C. A. Balanis (Second Edition, John Willey
and Sons Inc.)
[2.] Ultra Wideband Rose Leaf Microstrip Patch Antenna by A. A. Lotfi Neyestanak,
Islamic Azad University, Tehran, Iran
[3.] A Printed Crescent Patch Antenna for Ultra wideband Applications by Ntsanderh C.
Azenui & H. Y. D. Yang (IEEE Antennas & Wireless propagation Letters, Vol. 6,
2007)
[4.] Analysis, Design, and Measurement of Small and Low-Profile Antennas,
K.Hirasawa & M. Haneishi, London: Artech House, 1992.
[5.] Designing a GSM dipole antenna, TNE062 – RF System Design.