Final PPT

Design & Analysis of Fractal Elliptical Patch

Antenna

-Divya Sud (0709731043)-Prakhar Manas (0709731073)-Tanmay Vivek (0709731114)

Under the Supervision of - Mukhram Sir

Design of a Fractal Elliptical Patch antenna to work in cellular frequency range.

Constructing fractal structures of different specifications & iterations.

Analyze different area–perimeter relations of the process of fractal formation.

Problem Statement and Aims

Introduction to Patch Antenna

A Microstrip Patch Antenna

Microstrip antenna consists of various properties which make it very useful for many applications.

These properties include low profile, light weight, compact and conformable to mounting structure, easy fabrication and integratable with solid-state devices.

The results of these properties contributed to the success of microstrip antennas not only in military applications such as aircraft, missiles, rockets, and spacecraft but also in commercial areas such as mobile satellite communications, terrestrial cellular communications, direct broadcast satellite (DBS) system, etc

Properties

The Microstrip antenna is generally a single-layer design and consists of a radiating metallic patch or an array of patches situated on one side of a thin, non conducting, substrate panel with a metallic ground plane situated on the other side of the panel.

The metallic patch is normally made of thin copper foil or is copper-foil

plated with a corrosion resistive metal, such as gold, tin, or nickel. Each patch can be designed with a variety of shapes, with the most popular shapes being rectangular or circular.

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.

Advantages

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.

Disadvantages

Circular Patch Antenna A Circular Patch antenna has a circular metallic strip deposited on the Dielectric material.

Design Parameters

Resonant Frequency for TM(mn0) mode =

For TM(110) mode =

Now for Elliptical geometry –

Perimeter = 2π √( a^2 + b^2)/2

Also for ellipse =e = √(a^2 + b^2) 0<e<1

Combining these 2 formulas, we can find the required dimension of the Elliptical patch.

a

b

If we are specified with the dielectric constant (εr), the resonant frequency (fr), and the height of the dielectric layer (h) , then we can compute radius (a) as -

Antenna Terminology

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”.

1. Radiation Pattern

A radiation lobe is a “portion of the radiation pattern bounded by regions of relatively weak radiation intensity.” A major lobe is defined as “the radiation lobe containing the direction of maximum radiation.” 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.” A back lobe refers to a minor lobe that occupies the hemisphere in a direction opposite to that of the major lobe.

2. Beamwidth

The beamwidth of a pattern is defined as the angular separation between two identical points on opposite sides of the pattern maximum.Half-power beamwidth (HPBW ), 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 beamwidth is the angular separation between the first nulls of the pattern, and it is referred to as the first-null beamwidth (FNBW ).

3. Directivity

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.

4. Gain

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.

ThusG = 4πU(θ,φ)____ (dimensionless)

Pin(lossless isotropic source)

When the direction is not stated, the power gain is usually taken in the direction ofmaximum radiation.

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, beamwidth, polarization, side lobe level, gain, beam direction, radiation efficiency) are within an acceptable value of those at the centre frequency.

5. Bandwidth

Fractal technology

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.

Fractals in nature

Even shapes which are not self-similar can be fractals. The most famous of these is the Koch Snowflake.

First iterationKoch’s Snowflake

Length = (4/3)^2

Third iteration

Length = (4/3)^3

Second iterationsLength = 4/3

After n iterationsLength = (4/3)^n

Length = 1

Whole Process -

Sierpinski’s Triangle

The Sierpinski triangle has Hausdorff dimension [log(3)/log(2) ≈ 1.585], which follows from the fact that it is a union of three copies of itself, each scaled by a factor of 1/2.

Formation -

Other Examples1. Merger Sponge

2. Heighway Dragon Curve

3. Peano Curve

4. Gosper Curve

5. Space filling Tree

Fractal Antenna Antenna elements (as opposed to antenna arrays) made from self-similar shapes were first created by Nathan Cohen, starting in 1988.

A 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.

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.

This makes the fractal antenna an excellent design for wideband and multiband applications.

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.

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.

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.

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.

THE ACTUALPROJECT

Introduction

Understanding the effect of change in area and perimeter due to addition/ subtraction of Fractals.

We achieved it by modeling 3 test designs – 1. Increase in Area and Perimeter (1st and 2nd Additive

Iteration)2. Increasing Perimeter and Decreasing Area (1st and 2nd

Subtractive Iteration)3. Increasing Perimeter and making Area remain constant

(Normalised Iteration)

40 mm

30 mm

13.88 mm

e = .599

Elliptical Patch Antenna (0th Iteration)

Calculation done for the antenna to work optimally at 8 GHz.

Duroid Dielectric Layer (εr = 2.2)

Ground Plane (Copper)

Feed

Air Box

Elliptical Patch(Copper)

Microstrip Line (Copper)

Simulation Results

Magnitude of Electric Field

Mag E of the patch

S Parameter

Rectangular Plot Frequency v/s dB

Directivity

Rectangular Plot [Dir (dB) v/s Theta]

Polar Plot

Gain

Rectangular Plot[Gain (dB) v/s Theta

Polar Plot

Electric Field

Rectangular Plot[rE (dB) v/s Theta]

Polar Plot

Radiation Pattern

1st degree additive iteration

Right Triangular extensions were added to the ellipse after dividing it into 16 segments and extending each alternate segment as the triangle. Area and Perimeter both are increased.

Simulation Results


Mag E of the patch

S Parameter

Rectangular Plot S parameter v/s

Freq

Directivity

Rectangular Plot[Directivity (dB) v/s theta]

Polar Plot

Gain

Rectangular Plot[Gain (dB) v/s Theta]

Polar Plot

Electric Field

Polar Plot


Radiation Pattern

2nd degree additive iteration

Right Triangular Fractals were also added to the remaining 8 segments. Hence increasing area and perimeter by twice as in the last case.

Simulation Results


Mag E of the patch

S Parameter


Freq

Directivity


Polar Plot

Gain


Polar Plot

Electric Field


Polar Plot

Radiation pattern

1st degree subtractive iteration

Right Triangles are removed from the 8 alternating segments. This reduces the area, and increases perimeter. The perimeter increased is same as that in 1st additive iteration.

Simulation Results


Mag E of the patch


Freq

S Parameter


Polar Plot

Directivity

Polar Plot


Gain

Electric Field


Polar Plot

Radiation Pattern

2nd degree subtractive iteration

Right Triangles are removed from the remaining 8 segments. This reduces the area, and increases perimeter. The area removed is twice of the 1st subtractive iteration and perimeter increased is twice as that in 1st subtractive iteration.

Simulation Results


Mag E of the patch


Freq

S Parameter


Polar Plot

Directivity

Polar Plot


Gain

Electric Field


Polar Plot

Radiation Pattern

Normalised iteration

Right Triangular Fractals added and subtracted alternatively from the 16 segments. Hence (since the dimensions of the triangle were kept constant) one could say that no area was added or subtracted, while perimeter increased by the same value as in case of 2nd Degree Additive or Subtractive iteration.

Simulation Results


Mag E of the patch


Freq

S Parameter


Directivity

Polar Plot


Gain

Polar Plot

Electric Field


Polar Plot

Radiation Pattern

Comparison

Between Original Patch (Elliptical) and Final Patch (Normalised Iteration).

• Directivities

Normalised Antenna has higher Directivity

• Radiation Patterns

Normalised Fractal antenna has a more omni-directional nature (if only the front is considered

Conclusion – Hence we can say that the Normalised Fractal Elliptical Patch

antenna so formed is better than the Original Elliptical Patch antenna.

Between 1st order and 2nd order additive fractal.

• Frequency of operation-


From both the Directivity pattern and the Radiation pattern, it can be seen that the 1st Iterative fractal antenna is more directional than the 2nd Iterative fractal antenna.

Between 1st and 2nd Subtractive Iteration

•Frequency-


As can be seen from comparison of Radiation pattern, the directivity increases in the 2nd Iteration as compared to the 1st Iteration.

Conclusions

Fractal geometry increases the directivity of the antenna

Fractal geometry increases the wide band capacity of the antenna.

By keeping the area constant and increasing perimeter, one can achieve better Directivity while keeping the frequency the same.

On increasing the perimeter, the wideband capacity of the antenna, and the directivity of the antenna increases.

Fractal geometry increases Omni-directional characteristic of Elliptical Patch Antenna.

No direct relation between antenna area and frequency or directivity was computable from the experiments performed.

Analysis of Normalised Fractal Antenna

The Normalised Fractal antenna retained the frequency of the Original antenna

The Normalised antenna increased Directivity and Gain of the Original Antenna.

The Normalised fractal geometry increased the Omni-directional characteristic of the Elliptical antenna.

Hence it can be used better for applications which require Omni-directional signals, for example – Cellular Communication.

Thank You

Bibliography

Antenna Theory – Basics and Design by C. A. Balanis (Second Edition, John Willey and Sons Inc.)

Ultra Wideband Rose Leaf Microstrip Patch Antenna by A. A. Lotfi Neyestanak, Islamic Azad University, Tehran, Iran

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)

Analysis, Design, and Measurement of Small and Low-Profile Antennas, K.Hirasawa & M. Haneishi, London: Artech House, 1992.

Final PPT

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