IJRAR Research Journal
Fractal Antenna with Different Defective Ground Structure
(DGS)
Prajakta Madhukar Katkar
M.E
Electronics and Telecommunication Department
Pune Institute of Computer Technology, Pune, India
________________________________________________________________________________________________________
Abstract : Wireless technology is one of the main areas of
research in the world of communication systems. Microstrip antennas
are best choice for wireless application because of low weight,
easy to fabricate and low cost. But on the other side, less
bandwidth and less gain are the disadvantage of microstrip antenna.
So major issues for consideration are multiband and wideband
operation of antenna. For obtaining multiband and wideband
application, there are two different techniques introduced such as
fractal geometry and Defective Ground Structure (DGS). In this
paper, Fractal antenna with four shape of DGS has been proposed.
The antenna designed on FR4 substrate and a height 1.6mm is used.
The proposed antenna has been designed and simulated using High
Frequency Structure Simulator (HFSS) version 13.0.
IndexTerms – Fractal Antenna, Defective Ground Structure (DGS),
Return Loss.
________________________________________________________________________________________________________
I. Introduction
In wireless communication, microstrip patch antenna is very
useful because they are small, compatible and low cost. The
wireless applications such as IEEE 802.11a, Wi-MAX, HIPERLAN2, DCS,
PCS, UMTS, Bluetooth, WLANof IEEE 802.11b/g/h, satellite
communication are used. For these requirements, microstrip patch
antenna and fractal antenna are used. Microstrip patch antenna
designing consideration has four parts i.e., substrate, patch,
ground plane, and feeding. But microstrip patch antenna has few
disadvantages like poor efficiency, less power handling capacity
and narrow bandwidth.
Fractal antenna overcomes the disadvantages of a microstrip
patch antenna. The word fractal comes from Latin word “fractus”.
Fractal means have broken or fractured. Geometries and dimensions
of fractal structures are an important key factor for the operating
resonant frequencies. There are properties of fractal antennas like
space-filling, self-similarity, fractal dimensions. The main
advantages of fractals are miniaturization, wideband
characteristic, multiband characteristic and better efficiency. The
type of fractal antennas are Sierpinski Gasket, Sierpinski Carpet,
Koch curves, Minkowski, etc.
To improve the performance parameter of fractal antenna like
return loss, VSWR, bandwidth, defected ground structure (DGS) can
be introduced. [2] DGS also used for reducing the dimension. DGS is
an etched periodic or non-periodic cascaded arrangement defect in
the ground of a transmission which creates disturbance in the
shield current distribution. The various shapes of DGS such as
slot, arrow-shaped, dumbbell etc, are used in this project.[5]
This paper proposed four different DGS structures with fractal
antenna. Details of simulated and experimental results along with
designing parameter of proposed antennas are presented and
discussed.
II. Design of fractal antenna
For designing fractal antenna we used FR4 material as a
substrate which has dielectric constant 4.4. To design a fractal
antenna following formulae are used:-
· Effective dielectric constant:
is the width of patch, is the height of the substrate.
· Fringing factor:
· Calculate the length of patch (L) :
· Calculation the width () :
· Calculation of ground plane:
Where,
· VSWR (Voltage Standing Wave Ratio) is defined in terms of
input reflection coefficient:
· The Bandwidth of antenna is:
To measure bandwidth, return loss is should be below -10dB
Using above all formulae rectangular patch antenna is
implemented for the frequency then iterations are carried out
simple circular and square shaped. Square shape which tilts 45
degree in circular shape.
Table 1 Design parameter of patch antenna
Parameter
Values
Input Impedance
50
Frequency
3GHz
Dielectric Constant(
4.4
Height of substrate(h)
1.6mm
Table 2 Calculated Parameters for patch
Parameter
Values
Patch Width
30.4mm
Patch Length
23.43mm
Length Extension (
0.0736mm
Dielectric Constant()
4.03
Table 3 Calculated Parameters for Feedline
Parameter
Values
Line width (W1)
3.058mm
Line Length ( L1)
13.699mm
Table 4 fractal antenna design parameters and Dimensions
Parameters
Value(mm)
Patch L
23.43mm
Patch W
30mm
Height of Substrate
1.6mm
Dielectric constant
4.4
Substrate length
41mm
Substrate width
40mm
1st Patch corner cut
2.8mm*4.4mm
2nd Patch corner cut
1mm*1mm
1st circle radius
8.5mm
2nd circle radius
6mm
3rd circle radius
3.6mm
4th circle radius
2mm
III. simulation and results
In simulation process, we go step by step. Here, we start from
0th iteration and goes upto 3rd iteration.
Fig.1. 0th iteration of fractal antenna
Fig.2. Return loss of 0th iteration of fractal antenna
Fig.3. VSWR of 0th iteration of fractal antenna
Fig.4. 1st iteration of fractal antenna
Fig.5. Return loss 1st iteration of fractal antenna
Fig.6. VSWR of 1st iteration of fractal antenna
Fig.7. 2nd iteration of fractal antenna
Fig.8. Return loss of 2nd iteration of fractal antenna
Fig.9. VSWR of 2nd iteration of fractal antenna
Fig.10. 3rd iteration of fractal antenna
Fig.11. Return loss of 3rd iteration of fractal antenna
Fig.12. VSWR of 3rd iteration of fractal antenna
Above diagram shows all the iteration which shows simulation
result of return loss and VSWR. From 0th to 3rd iteration it shows
that they are reduces the size and gives the multiband operation.
But it resonates at higher frequencies. So we want fractal antenna
resonates on both low and high frequency. For this purpose we use
Defective Ground Structure. Also, for improvement in bandwidth we
use Defective Ground Structure.
Fig.13. Front view of fabricated design of 3rd iteration of
fractal antenna
Discussing various shapes of Different Defective Ground
Structures (DGS) is as follows:
1. Fractal antenna with Rectangular Slot DGS:
Front View
Back View
Fig.14. Simulated design of Fractal antenna with Rectangular
slot DGS
Front View Back View
Fig.15. Fabricated design of Fractal antenna with Rectangular
slot DGS
Return loss:
Fig.16. Simulated result of return loss for Fractal antenna with
rectangular slot DGS
Fig.17. VNA result of return loss for fractal antenna with
Rectangular slot DGS
Table5.Table of return loss for fractal antenna with Rectangular
slot DGS
DGS
Return Loss Result
Simulated
Fabricated
Rectangular slot DGS
8.3GHz=-23.04dB
9.7GHz=-18.194dB
11.5GHz=-14.78dB
14.1GHz=-14.47dB
8.34GHz=-24.60dB
9.97GHz=-17.577dB
11.59GHz=-16.74dB
14.11GHz=-14.69dB
The above table shows the result of simulated return loss and
fabricated result on VNA. The rectangular slot DGS gives four
resonant frequencies. In rectangular slot DGS, antenna resonates on
higher frequencies.
VSWR:
Fig.18 Simulated VSWR of Fractal antenna with rectangular slot
DGS
Fig.19 VNA result of VSWR for fractal antenna with rectangular
slot DGS
Table6. VSWR for fractal antenna with Rectangular slot DGS
DGS
VSWR Result
Simulated
Fabricated
Rectangular slot DGS
8.3GHz=1.13
9.7GHz=1.28
11.5GHz=1.44
14.1GHz=1.46
8.34GHz=1.16
9.97GHz=1.30
11.59GHz=1.35
14.11GHz=1.46
The above table shows the simulated and fabricated result of
VSWR. The VSWR should be less than 2 so, this antenna gives VSWR
values less than 2.
3D Polar Plot:
Fig.20. 3D polar plot of fractal antenna with rectangular slot
DGS
Radiation Pattern:
Fig.21 Radiation pattern of fractal antenna with rectangular
slot DGS
The Fig.20 and Fig.21 shows the 3D-polar plot and radiation
pattern respectively.
2. Fractal antenna with Arrow-shaped DGS:
Front View
Back View
Fig.22. Simulated design of fractal antenna with arrow-shaped
DGS
Front View Back View
Fig.23. Fabricated design of fractal antenna with Arrow-shaped
DGS
Return loss:
Fig.24. Simulated return loss result of fractal antenna with
arrow-shaped DGS
Fig.25. VNA result return loss of fractal antenna with
arrow-shaped DGS
Table7. Table of return loss for fractal antenna with
Arrow-shaped DGS
DGS
Return Loss Result
Simulated
Fabricated
Arrow-shaped DGS
5.7GHz=-17.496dB
7.9GHZ=-19.629dB
8.9GHZ=-17.401dB
11.8GHz=-21.31dB
14GHz=-17.467dB
5.79GHz=-12.42dB
8.04GHz=-21.469dB
9.02GHz=-17.322dB
12.14GHz=-24.68dB 13.97GHz=18.574dB
Above table shows the simulated and fabricated results of return
loss for fractal antenna with Arrow-shaped DGS. This antenna gives
five multi-resonant frequencies.
VSWR:
Fig.26. Simulated VSWR result of fractal antenna with
arrow-shaped DGS
Fig.27. VNA result of VSWR on VNA of fractal antenna with
arrow-shaped DGS
Table8. Table of VSWR for fractal antenna with Arrow-shaped
DGS
DGS
VSWR Result
Simulated
Fabricated
Arrow-shaped DGS
5.7GHz=1.30
7.9GHZ=1.23
8.9GHZ=1.31
11.8GHz=1.18
14GHz=1.309
5.79GHz=1.64
8.04GHz=1.17
9.02GHz=1.31
12.14GHz=1.14
13.97GHz=1.27
Above table shows the simulated and fabricated results of VSWR
for Fractal antenna with Arrow-shaped DGS.
3D-Polar Plot:
Fig.28. 3D- polar plot of fractal antenna with arrow-shaped
DGS
Radiation Pattern:
Fig.29. Radiation pattern of fractal antenna with arrow-shaped
DGS
Fig.28 and Fig.29 shows the 3D-polar plot and radiation pattern
of fractal antenna with arrow-shaped DGS.
3. Fractal antenna with Dumbbell- shaped DGS:
Front View
Back View
Fig.30. Simulated design of fractal antenna with Dumbbell-shaped
DGS
Front View Back View
Fig.31. Fabricated design of fractal antenna with
dumbbell-shaped DGS
Return Loss:
Fig.32. Simulated return loss result of fractal antenna with
dumbbell shaped DGS
Fig.33. VNA result of return loss for fractal antenna with
dumbbell shaped DGS
Table9. Table of return loss for fractal antenna with
Dumbbell-shaped DGS
DGS
Return Loss Result
Simulated
Fabricated
Dumbbell-shaped DGS
2.3GHz=-12.87dB
6.5GHz=-12.39dB
7.6GHz=-21.38dB
9.3GHz=-23.99dB
11GHz=-15.86dB
12.1GHz=-18dB
13.8GHz=29.47dB
2.4GHz=-10dB
6.64GHz=-14.41dB
7.93GHz=21.115dB
9.02GHz=-21.15dB
10.03GHz=24.099dB
12.31GHz=-19.40dB
Above table shows the simulated result and fabricated result of
return loss for fractal antenna with Dumbbell-shaped DGS. It gives
the six multi-resonant frequencies which mean it has six multiband
operations. When we use dumbbell-shaped DGS, it resonates at both
low and high frequencies. Dumbbell- shaped DGS give better result
than rectangular slot DGS and Arrow-shaped DGS.
VSWR:
Fig.34. Simulated VSWR result of fractal antenna with dumbbell
shaped DGS
Fig.35. VNA result of VSWR for Fractal antenna with dumbbell
shaped DGS
Table10. Table of VSWR for fractal antenna with Dumbbell-shaped
DGS
DGS
VSWR Result
Simulated
Fabricated
Arrow-shaped DGS
5.7GHz=1.30
7.9GHZ=1.23
8.9GHZ=1.31
11.8GHz=1.18
14GHz=1.309
5.79GHz=1.64
8.04GHz=1.17
9.02GHz=1.31
12.14GHz=1.14
13.97GHz=1.27
3D-Polar Plot:
Fig.36 3D-polar plot of fractal antenna with dumbbell shaped
DGS
Radiation Pattern:
Fig.37 Radiation pattern of fractal antenna with dumbbell shaped
DGS
Fig.36 and Fig.37 show the 3D-polar plot and radiation pattern
respectively.
4. Fractal antenna modified ground with L-shaped DGS:
Front View
Back View
Fig.38 Simulated Design of Fractal antenna modified ground with
L-shaped DGS
Front View Back View
Fig.39. Fabricated Design of fractal antenna modified ground
with L-shaped DGS
The L-shaped DGS is used to increases the impedance matching in
the UWB frequencies. When two L-shaped DGS placed in ground plane,
which moderate the reflection of surface current so, it adjust the
antenna impedance and reduces the return loss.[3]
Return Loss:
Fig.40 Simulated return loss result of fractal antenna modified
ground with L-shaped DGS
Fig.41 VNA result of return loss on VNA of fractal antenna
modified ground with L-shaped DGS
Table11. Table of return loss for fractal antenna modified
ground with L-shaped DGS
DGS
Return Loss Result
Simulated
Fabricated
Modified ground with L-shaped DGS
0.96GHz=-10.01dB
15GHz=-12.91dB
(ultra-wideband)
1.63GHz=-11.625dB
14.34GHz=10.693dB
(ultra-wideband)
Above table shows the simulated results and fabricated results
of fractal antenna with modified ground with L-shaped DGS. It gives
ultra-wideband operation which operates on 0.96GHz to 15GHz.Because
of DGS technique it enhance the bandwidth which use for high data
speed in wireless application.[6]
VSWR:
Fig.42 simulated result of VSWR of Fractal antenna modified
ground with L-shaped DGS
Fig.43 VNA result of VSWR on VNA of Fractal antenna modified
ground with L-shaped DGS
Table11. Table of VSWR for fractal antenna modified ground with
L-shaped DGS
DGS
VSWR Result
Simulated
Fabricated
Modified ground with L-shaped DGS
0.96GHz=1.8
15GHz=1.5
(ultra-wideband)
1.63GHz=1.708
14.34GHz=1.852
(ultra-wideband)
3D- Polar Plot:
Fig.44 3D-Polar plot of fractal antenna modified ground with
L-shaped DGS
Radiation Pattern:
Fig.45 Radiation pattern of fractal antenna modified ground with
L-shaped DGS
Fig.44 and fig.45 shows the 3Dpolar plot and radiation pattern
of fractal antenna modified ground with L-shaped DGS. In radiation
pattern, it is omni-directional in H-plane at frequency 3GHz.
.
IV. Conclusion
In this paper, we studied four defective ground structures with
fractal antenna. There are three DGS on full ground and one
modified ground with DGS. It gives multiband operation as well as
ultra-wideband operation. The Slot DGS, arrow-shaped DGS and
dumbbell-shaped DGS give multiband operation. Slot DGS resonate at
only higher frequencies but arrow-shaped DGS and dumbbell shaped
DGS resonates at low and high frequencies. The another one DGS is
modified ground with L-shaped DGS give ultra-wide band operation
which means 3.1GHz-10.6GHz frequency ultra-wideband operates but
this antenna operates at 0.96GHz-15GHz. The modified ground with
L-shaped DGS gives better antenna efficiency (95%) than other three
antennas. The proposed antennas are useful for wireless local area
application, satellite communication, and military application.
References
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Kumar, “Defectied Ground Structure: Fundamentals, Analysis, and
Applications in Modern Wireless Trends”, International Journal Of
Antenna and Propagation, 2017
[3] Bharti Gupta, Sangeeta Nakhate, Madhu Shandilya, “A compact
UWB Microstrip Antenna with Modified Grround Plane For Banwidth
Enhancement”, International Journal of Computer Application, Vol
49,July 2012
[4] Contantine A. Balanis, “ Antenna Theory, Analysis and
Design”, A John Wiley & Sons, INC., Publication, United State
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[5] Gary Breed, “An Introduction to Defected Ground Strucutures
in microstrip Circuits”, High Frequency Electronics, Summit
Technical Media LLC, November 2008
[6] Iram Nadeem and Dong-You Choi, “Broadband Printed Antenna
with Modified Rectangular Patch and U-Slot in Ground Plane”,
Radioelectronics and Communication Systems, Vol.61 , N0. 12,
2018
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