H shape defected ground structure dgs- embedded square patch antenna

1. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 1, January (2015), pp. 73-79 © IAEME
73
H-SHAPE DEFECTED GROUND STRUCTURE (DGS)
EMBEDDED SQUARE PATCH ANTENNA
Vidyadhar S Melkeri1
, S L Mallikarjun2
P V Hunagund3
1,2,3
Department of PG Studies and Research in Applied Electronics Gulbarga University Kalaburgi
ABSTRACT
In this paper microstrip patch antenna is designed for 2.4GHz frequency. For the antenna
miniaturization and bandwidth improvement H-shaped DGS on microstrip patch antenna (MSA) is
used. The design of DGS has been analyzed for different dimensions of H-slot and achieved
optimized dimensions.The simulation process has been done through Finite Element Machine (FEM)
based software High Frequency Structure Simulator (HFSS) software. The properties of antenna
such as reflection co-efficient, bandwidth andgain are determined and compared with the properties
of single element square patch antenna.Further proposed antennas performance is studied for
different size of defect on the same patch antenna. Proposed antenna finds its application in wireless
LAN protocols such as Bluetooth, IEEE 802.11 and in 2.4GHz ISM Band.
Keywords: DGS, HFSS, MSA, Bandwidth, Reflection co-efficient.
1. INTRODUCTION
The microstrip patch antenna is one of the most useful antennas for low cost and compact
design for RF applications and wireless systems. In wireless mobile communication and satellite
applications, microstrip antenna has attracted much interest because of their small size, low cost on
mass production, light weight, low profile and easy integration with the other components [1-2].
Although microstrip patch antennas have many very desirable features, they generally suffer from
limited bandwidth. So the most important disadvantage of microstrip resonator antenna is their
narrow bandwidth. To overcome this problem without disturbing their principal advantage (such as
simple printed circuit structure, planar profile, light weight and cheapness), a number of methods and
structures have recently been investigated.
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2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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An individual microstrip patch antenna has a typical gain of about 6 dB. Several approaches
have been used to enhance the bandwidth by perturbing the higher order mode by interpolating
surface modification into patch geometry. Gain enhancement by cutting rectangular hole on another
inserted layer. A symmetrical hole on the inserted layer is used which is the major frequency in
modern wireless communication era [3].multilayer structures [4], broad folded flat dipoles [5],
curved line and spiral antennas [6], impedance matched resonator antennas [7], resonator antennas
with capacitive coupled parasitic patch element [8], log periodic structures [9], But the most unique
technique to reduce the size of patch is to defect the ground. While comparing the antenna with the
defected ground structure and the antenna without the defected ground, the antenna having defected
ground structure reduces the size of antenna [10]. The percentage of reduction of size depends upon
the ground area that is defected. Defected Ground Structure disturbs the shielded current distribution
that depends on the dimension and shape of the defect. The current flow and the input impedance of
antenna are then influenced by the disturbance at shielded current distribution due to the DGS
structure. The DGS structure can also be used to control the excitation and the electromagnetic
waves propagating through the substrate layer [11]. A defect in the ground plane causes to increase
in effective capacitance and inductance. In this paper, microstrip antenna for low frequency at 2.4
GHz is designed and simulated using the HFSS software.
2. ANTENNA DESIGN PARAMETERS
For the designing of square microstrip patch antenna, the following equations are used to calculate
the dimensions of the square microstrip patch antenna [11].
Design consideration for required frequency.
Length L, usually 0.333 ߣ଴< L < 0.5 ߣ଴
t<<ߣ଴ patch thickness
Height of substrate h, usually 0.003 ߣ଴ ≤ h ≤ 0.05 ߣ଴
The dielectric constant is considered 2.2 ≤∈௥≤ 12
An effective dielectric constant ߝ௥௘௙௙ must be obtained in order to account for the fringing and the
wave propagation in the line. The value of ߝ௥௘௙௙is little less thanߝ௥because the fringing fields around
the edge of the patch are not confined in the dielectric substrate but are also spread in the air. The
expression for ߝ௥௘௙௙can be given as:
ߝ௥௘௙௙ =
ߝ௥ + 1
2
+
ߝ௥ − 1
2
൤1 + 12
ℎ
ܹ
൨
భ
మ
The dimensions of the patch along its length have now been extended on each end by a distance ∆L,
which is given empirically as:
∆‫ܮ‬ = 0.412ℎ
(ߝ௥௘௙௙ + 0.3) ቀ
ௐ
௛
+ 0.264ቁ
(ߝ௥௘௙௙ − 0.258) ቀ
ௐ
௛
+ 0.8ቁ
The effective length of the patch‫ܮ‬௘௙௙now becomes:
‫ܮ‬௘௙௙ = ‫ܮ‬ + 2∆‫ܮ‬
For a given resonance frequency ݂଴ the effective length is given by as:
‫ܮ‬௘௙௙ =
‫ܥ‬
2݂଴ඥߝ௥௘௙௙

3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 1, January (2015), pp. 73-79 © IAEME
75
For a rectangular microstrip patch antenna, the resonance frequency for any ܶ‫ܯ‬௠௡mode is givenby
as:
݂଴ =
‫ܥ‬
2ඥߝ௥௘௙௙
൤ቀ
݉
‫ܮ‬
ቁ
ଶ
+ ቀ
݊
ܹ
ቁ
ଶ
൨
భ
మ
Where m and n are modes along L and W respectively
For efficient radiation, the width W is given as:
ܹ =
‫ܥ‬
2݂଴ට
(ఌೝାଵ)
ଶ
Substrate dimensions given as:
‫ܮ‬௚ = 6ℎ + ‫ܹ &ܮ‬௚ = 6ℎ + ܹ
Where,
h = substrate thickness
L = length of patch
‫ܮ‬௘௙௙ = effective length
W = width of patch
c = speed of light
݂଴= resonant frequency
ߝ௥= relative permittivity
ߝ௥௘௙௙= effective permittivity
‫ܮ‬௚ = Length of ground plane
ܹ௚ = Width of ground plane
Based on the above formulae a conventional square patch antenna has been designed with thickness
of substrate as h=0.16cm and relative permittivityߝ௥ = 4.2. From the analysis the length and width of
patch are 3.01 cm and 3.01 cm respectively and length and width of substrate are 7.2cm and 4.2cm
respectively.The proposed antenna is fed by using microstrip line feed method. Figure 1 shows the
top view of conventional square MSA.
Figure 1: Top view of conventional square MSA

4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
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76
The H-shaped DGS [12]has been embedded in the ground plane of the proposed antenna
which consists of the two rectangular slots and one rectangular connecting slot in the ground plane as
shown inFigure 2. Figure 3 it shows the bottom view of proposed antenna with DGS.
Figure 2: Shape of the defect in ground plain Figure 3: Bottom view of proposed DGS antenna
3. RESULTS AND DISCUSSION
The S11 parameters for the proposed antennas are calculated and simulated reflection
coefficients results are presented and compared with each otherand are shown in Figure 4.
Figure 4: Reflection co-efficient verses frequency graph.

5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 1, January (2015), pp. 73-79 © IAEME
77
From the above figure it is observed that antenna-1 is resonating at 1.61 GHz with impedance
bandwidthof 500MHz when compared to conventional antenna, antenna-1 is showing improved
impedance bandwidth of 200MHz. Further all compared results are tabulated in Table-1.
Since the proposed antenna with DGS are resonating below the designed frequency. The size
reduction value when compared with conventional antenna in terms of percentage is also tabulated.
Table 1: Antenna parameters
ANTENNAS
Dimensions
of DGS
Resonating
Frequency
in GHz
Reflection
coefficient
BW
%
BW in
MHz
Size
Reduction in
%A B
Conventional - - 2.36 -16.50dB 1.27 300 0
Antenna-1 0.4 1.2 1.61 -26.6dB 3.12 500 49.06
Anteena-2 0.3 1.4 1.59 -24.25dB 3.11 510 50.94
Antenna-3 0.2 1.6 1.48 -23.20dB 3.36 500 62.16
Anteena-4 0.1 1.8 1.45 -16.93dB 2.73 400 65.51
The radiation patterns of the proposed antennas are shown in Figure-5 to Figure-9.From
thefigures it is observed that for conventional antenna the radiation pattern is broadsided which is as
shown in Figure 5 and for other antennas with DGS radiation pattern is observed to be nearly Omni
directional in azimuth plain as shown in Figure-5 to Figure-9.
Figure 5: Radiation pattern of conventional antenna Figure 6: Radiation pattern of Antenna-1
Figure 7: Radiation pattern of Antenna-2 Figure 8: Radiation pattern of Antenna-3

6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 6, Issue 1, January (2015), pp. 73-79 © IAEME
78
Figure 9: Radiation pattern of Antenna-4
Gain is a very important parameter of every antenna. Basically, the gain is the ratio of the
radiated field intensity by test antenna to the radiated field intensity by the reference antenna [9]. In
this study, the gain of antenna is improved with DGS which is found to be 8.25dB when compared
with conventional square MSA (4.62dB).
The smith chart of antenna is shown in figure 10 andit is observed that impedance matching
is good.
Figure 10: Smith chart of antenna – 4
4. CONCLUSION
From the detailed study it is observed that the conventional antenna is designed for 2.4GHz
and further an H-shaped DGS is incorporated exactly below the patch and by doing this it is
observed that antenna is resonating at the lower frequencies. By varying the dimensions of ‘a’ and
‘b’ of DGS it is further obtained that resonating frequency is shifting to lower frequency and from
the comparative study the obtained maximum size reduction is 65.51%. By embedding DGS
bandwidth, radiation pattern and gain are also improved.These antennas find applications in wireless
LAN protocols such as Bluetooth, IEEE 802.11 and in 2.4GHz ISM Band.

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