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Investigation on Radiation Improvement of Corner Truncated Triband
Square Microstrip Patch Antenna with Double Negative Material
Shobhit K. Patel1 and Yogeshwar Kosta2, Member, IEEE
1Assistant Professor, Charotar University of Science and Technology, Changa-388421, Gujarat,
India
2Director, Marwadi Education Foundation’s Group of Institutions, Rajkot, Gujarat, India
1shobhit_65@yahoo.com
Abstract— In this paper, we have reported a truncated square microstrip patch antenna loaded
with double negative material and conventional dielectric material. Metamaterials exhibit
qualitatively new electromagnetic response functions that cannot be found in the nature. The
inclusion of these structures allows simultaneous operation over several frequencies. We have
designed an antenna loaded with metamaterial to work in three bands in the frequency range of
0.5-2.0 GHz. The designed antenna loaded with metamaterial has three working frequency
bands. We have shown a comparative analysis of this metamaterial loaded antenna with
conventional antenna. The designed antenna loaded with metamaterial has several wireless
applications. Design results are obtained by High Frequency Structure Simulator (HFSS), that is
used for simulating microwave passive components.
Keywords- Double Negative (DNG), Single negative (SNG), Metamaterial, Left-handed (LH),
Split ring resonator (SRR).
2
1. INTRODUCTION
The rapid development of electronics and wireless communications has led to greater demand
for wireless devices that can operate at different standards such as the universal mobile
telecommunications system UMTS, bluetooth, wireless local-area network (WLAN) and also
satellite communications. However, the E-shape microstrip patch antenna for GPS application is
shown [1]. Additionally, many applications, such as mobile devices, demand that the antenna be
very compact. These two requirements have triggered research on the design of compact and
single or multiband antenna operation [2]. Microstrip patch antennas are widely used because of
their many merits, such as the low profile, light weight and conformity. However, patch antennas
have a main disadvantage: narrow bandwidth. Researchers have made many efforts to overcome
this problem and many configurations have been presented to extend the bandwidth [4].
Microstrip patch antennas are widely used in wireless devices and other compact sizes with
multiband antenna operation. Microstrip patch antennas can be meandered and circularly
polarized by slot geometry [3-5].
Metamaterials exhibit qualitatively new electromagnetic response functions which cannot be
found in the nature. The prefix “meta-” is of Greek origin and is translated as “outside of" thus
the term "metasubstances" may be interpreted as structures whose effective electromagnetic
behavior falls outside of that of its constitutive elements. The analysis of publications on various
aspects of metamaterials technology allows classifying all varieties of artificial environments
depending on their effective values of permittivity (ε) and magnetic permeability (µ). The idea of
complex materials in which both permittivity and permeability possess negative real values at
certain frequencies has received considerable attention (see e.g., [6] -[29]). In 1967, Veselago
3
theoretically investigated plane wave propagation in a material whose permittivity and
permeability were assumed to be simultaneous negative [10]. His theoretical study showed that
for a monochromatic uniform plane wave in such a medium the direction of the Poynting vector
is antiparallel to the direction of phase velocity, contrary to the case of plane wave propagation
in conventional simple media. Smith et al. constructed such a composite medium for the
microwave regime, and demonstrated experimentally the presence of anomalous refraction in
this medium [6]. For metamaterials with negative permittivity and permeability, several names
and terminologies have been suggested, such as “left-handed” media, media with negative
refractive index, “backward wave media” (BW media), “double negative (DNG)” metamaterials,
to name a few.
Many research groups all over the world are now studying various aspects of this class of
metamaterials, and several ideas and suggestions for future applications of these materials have
been proposed. As for methods of constructions, several geometries for the inclusions of such
media have been suggested. Among those, one can mention the thin wire and the split ring
resonators (SRR) used originally by Smith, Schultz and Shelby [6], [9], inspired by the work of
Pendry [8], negative permittivity and permeability by Ziolkowski and Heyman [12]. Recently the
double negative metamaterial have attracted much attention because they have a series of unique
electromagnetic properties such as negative refraction phenomenon. Tang et al. constructed dual
band epsilon negative material design using folded wire [13], Duan et al. shown progress in
reversed chernkov radiation in DNG metamaterial [14], L-shaped chiral negative index structure
simulated by Li, Yang and Dong [15], compact DNG metamtarial based resonators designed by
Karamonos, Dimitriadis and Kantartzis [16], Wang et al. studied scattering of metallic
columncovered by DNG Metamaterial [21], Daniele et al. designed cylindrical resonator filled
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with DNG Metamaterial [22], negative refraction by plasma metamaterial studied by Guo [24],
the multiband metamaterial design shown by Patel and Kosta [26].
The topic of metamaterials, especially engineered media with unconventional response
functions not readily found in natural materials, has received ever increasing attention in recent
years. In particular, media in which one or both of the material parameters, permittivity and
permeability, can attain negative real parts in a certain frequency band, have been the subject of
study by numerous groups. When both material parameters possess negative real parts, such
double negative media can support wave propagation and exhibit the peculiar phenomenon of
negative refraction, while media with a single-negative parameter, such as plasmonic media
(e.g., noble metals in the IR and visible regimes) support evanescent wave. DNG and SNG
metamaterials, formed by embedding arrays of metallic split-ring resonators and wires in a host
medium, have been successfully constructed in the microwave regime by several groups, and
some of their unusual properties (e.g., negative refraction) have been experimentally
demonstrated [28]. One of the interesting research directions in DNG (or left-handed “LH”)
metamaterials is the development of such materials in the infrared (IR) and visible regimes. In
these frequency regimes, constructing DNG and µ-negative (MNG) materials are challenging, in
part due to the fact that in these frequency regimes the magnetic permeability due to the
molecular currents in a material tends to approach to the free space permeability [29].
2. DESIGN AND MODELING
Calculation for Metamaterial (Double Negative Material)
Maxwell’s equations:
(1)
D
t
H
5
(2)
B
t
E
From the point of view of Maxwell’s Equations, the material is some collection of objects
(whether atoms, molecules, composites or anything else) that can be described by Permittivity (ε)
and a Permeability (µ) [30].
Permittivity (ε) and Permeability (µ) measurements:
The constitutive parameters are the permittivity and the permeability, which are related to the
refractive index n by
(3)
rr
n
Where, εr and µr are the relative permittivity and permeability related to the free space
permittivity and permeability by
(4)
1-
mf
12-
108.854
0 r
(5) m)s/(Av
-7
104
0
r
The reflection coefficient (Γ) at the interface is found from the measured reflection (S11) and the
transmission (S21) coefficients [31].
(6) 1
2
XX
Where,
(7)
21
11
2
21
2
11 S
SS
X
The propagation factor P is found from S11, S21 & Γ
(8)
12111
2111
SS SS
P
6
The complex dielectric constant and permeability can be determined from P and Γ:
(9)
11 22
0
r
2
c
r
(10)
1
ln
211 2
2
pl
(11)
11
1
1
22
0
c
r
Where,
λ0 is the free space wavelength
λc is the cutoff wavelength of the transmission line section
Equations (6–8) show how the reflection coefficient (Γ) and the propagation factor (P) is
related to transmission coefficients. Equations (9-11) show how permeability and complex
dielectric constant is related to reflection coefficient (Γ) and the propagation factor (P). In a way
these equations show how permeability and complex dielectric constant is related to transmission
coefficients [31].
Let us consider a patch with length L and width W above a substrate composed of a dielectric
material with permittivity εr. The frequency of operation of an antenna is f0 and thickness of the
substrate is t then the width of patch W is given by the Equation (12) [26].
(12)
21
20
r
f
c
W
Where c is the speed of light. Here we have used a square patch, so the width (W) and length (L)
of the patch are identical. We have calculated the length and width of the patch to be 56.4 mm;
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as the patch is square, the substrate length and width are chosen to be 66.4 mm. By truncating the
corners we get better response compared to the simple patch.
The resonance frequency of the microstrip antenna (MSA) excited at any TMmn mode is
obtained by using the following expression [32]:
(13)
1/2
2
W
2
L
n
2
t
m
2
p
c
mnp
r
f
Where t is the thickness of the substrate, W is the width of the patch, and L is the length of the
patch and m, n and p are the modes along the thickness t, length L and width W of the patch,
respectively.
By using Equation (12), we get the patch width 56.5 mm and as we used a square patch its
length and width are same, for both conventional material substrate and DNG material substrate
the patch size remains same. Here two designs are shown in Figure 1 and Figure 2, the first
design is with conventional material as shown in Figure 1 and second design is with double
negative material substrate with metallic inclusions as shown in Figure 2. All the other things
apart from the substrate material are same for both the designs. The thickness of the substrate is
kept small (compared to the length and width of the antenna) so that the shorter co-axial probe is
required and thus less probe inductance is induced. Figure 1 and 2 depicts the geometry of the
proposed patch antenna. The square patch, with dimensions of 56.4×56.4 mm2 is supported by a
thin dielectric substrate with dielectric permittivity ε (16.5) with material diamond [26] [34], and
it is in between the patch and the ground plane. In this substrate metallic inclusions are added to
make the DNG material as shown in Figure 2. The substrate is very thin and its thickness is 2
mm as shown in Figure 1 (b) and 1 (b). The feed of the antenna is located at (7mm, 7mm) from
the center left of the antenna as shown in Figure 1 (a) and 2 (a). Here the patch is truncated at the
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one corner as shown in the Figure 1 and 2. Here the corner is truncated 12.2 mm. The feed is
located as shown in the design. Split ring resonators are used as metallic inclusions to make
DNG material. Inclusion of these structures allows simultaneous operations over several
frequencies. An SRR structure can give rise to both electric and magnetic plasmonic resonance
depending on the orientation of the gap with respect to the incident electric field. When a wave
is incident on the SRR, the alternating H-field induces a current in the loop of the SRR that
results in a varying voltage across the gap within the SRR and between adjacent SRRs. In the
case of the double SRR as shown in Figure 2(c), the inner and outer ring gap positions are
different. Therefore, the inner ring and the outer ring have different surface charge densities at
corresponding positions those results in a capacitive coupling between the inner ring and the
outer ring. The directivity of the antenna is increased by using metamaterial substrate.
The key component SRR provide a negative effective permeability µeff (due to a resonance of
circular currents around the SRR) and a negative effective permittivity εeff with frequency ω'
greatly reduced compared to that of bulk metal ω, as a result mainly of the magnetic field energy
dominating the kinetic energy of the current carrying electrons [26]. The antiparallel Poynting
and wave vector exhibited by LHMs enables an interesting application, such as negative
refraction. SRRs behave as an LC resonator that can be excited by an external magnetic flux,
exhibiting a strong diamagnetism above their first resonance. SRRs also exhibit cross-
polarization effects (magneto electric coupling) so that excitation by a properly polarized time-
varying external electric field is also possible. Fig. 2 (c) shows the basic topology of the SRR, as
well as the equivalent-circuit model and electric and magnetic field in SRR. In this Fig 2 (c), C
stands for the total capacitance between the rings, i.e., C=πl2Cpul where Cpul is the per unit
length capacitance between the rings. The resonance frequency of the split ring resonator is
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given by f = (LCs) -1/2/2π, where Cs is the series capacitance of the upper and lower halves of the
SRR, i.e., Cs = C/4. The inductance L can be approximated by that of a single ring with length l2
and width e as shown in Fig. 2 (c). Thus, the SRR can be mainly considered as a resonant
magnetic dipole that can be excited by an axial magnetic field. Now the resonance in SRR will
ultimately change the properties of the original substrate. The material properties both magnetic
and electric changes now and previously dielectric material now behaves as DNG material and
the permittivity and permeability of the material is changed. So the entire substrate behaves as a
DNG material with different permittivity and permeability and refractive index also changes due
to change in permittivity and permeability.
The frequency region above about 500 MHz and below 2 GHz represents an awkward design
problem for high sensitivity magnetic resonance. Here we want to maximize the product ηQ
where η is the filling factor and Q is the quality factor of the resonator.
)(14
2
2
1
1
2
1
11
2
1
1
1
A
A
l
l
l
d
A
A
l
Q
Where
2
1
0
2
d
is skin depth, A1=l12 and A2= (l2-e) 2- (l1+d) 2, σ is the conductivity of the
material. In Fig. 2 (c) thickness of ring d and e both are 1mm and, t is 2mm.
At room temperature conductivity of copper, 58000000 Ω/m, results in a skin depth δ of
1.6x10-3 mm. Thus for a resonator with l1 = 24 mm the expected Q is over 3,000. For finite
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length resonators, the filling factor η, and field homogeneity are similar to those of a single layer
solenoid of the same size in the limit of low frequency. Values of η can easily exceed 0.5; the
product ηQ which determines the S/N ratio could thus be over 1,500. Simulations and results for
both designs have been discussed in section 3.
Figure 1 (a). Design 1 for conventional material (top view)
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Figure 1 (b). Design 1 for conventional material (front view)
Figure 2 (a). Design 2 for DNG material (top view)
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Figure 2 (b). Design 2 for DNG material (front view)
Figure 2 (c). (i) Split Ring Resonator (SRR) unit cell, (ii) Equivalent electric circuit of the SRR
unit cell
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Table 1. shows details about the material. Let us consider patch made from Cu on the
diamond substrate. Ground beneath substrate is also of Cu.
Table 1. Material Used for Patch Antenna
Material
Patch
Copper (Cu)
Substrate
Diamond
(ε=16.5)
[26][34]
3. SIMULATION RESULTS AND DISCUSSIONS
For the simulation, we used High Frequency Structure Simulator version 11 (HFSS 11) of ansoft,
which is very good simulator for RF antennas. After simulating the design the result we got as
follows.
Fig. 3 shows the Return loss and Voltage Standing Wave Ratio (VSWR) of the design 1 and
Table 2 shows values of them for different band with its center frequencies for design 1. Fig. 4
shows the Return loss and VSWR of the design 2 and Table 2 show values of them for different
band with its center frequencies for design 2. For the entire band VSWR is less than 2.
14
.
Figure 3 (a) Return loss (S11) parameter of the antenna for design 1 (conventional material)
Figure 3 (b). VSWR of the antenna for design 1 (conventional material)
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Figure 4 (a). Return loss (S11) parameter of the antenna for design 2 (DNG material)
Figure 4(b). VSWR of the antenna for design 2 (DNG material)
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Table 2. Return loss (S11) and VSWR comparison
Band
Material
Frequency
GHz
Minimum
Return loss
(S11)
dB
VSWR
First
Conventional
0.66
-17
1.5
DNG
0.68
-20
1.3
Second
Conventional
1.27
-17
1.6
DNG
1.33
-21
1.3
Third
Conventional
1.44
-14
1.5
DNG
1.41
-33
1.2
Table 2 shows the comparison of Return loss and VSWR for the two designs. As shown in the
table, for DNG material the VSWR and Return loss values are better compared to the
Conventional material. There is not much difference in the first and second band but the third
band shows very good result in DNG material design compare to the conventional material
design.
Figure 5 (a) Polar Plot (Gain total) of the antenna for design 1 (conventional material) (b) Polar
Plot (Gain total) of the antenna for design 2 (DNG material)
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Figure 5 shows the polar plot (gain) for conventional material and DNG material respectively.
Different color shows the intensity of the field in that direction. Comparing the two designs we
found that the design with DNG material has the proper orientation of radiation, and intensity is
also good for the design compared to the conventional material design.
Figure 6 (a) Radiation pattern (Gain total) of the antenna for phi 0˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
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Figure 6 (b) Radiation pattern (Gain total) of the antenna for phi 70˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
Figure 6 (c) Radiation pattern (Gain total) of the antenna for phi 140˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
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Figure 6 (d) Radiation pattern (Gain total) of the antenna for phi 210˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
Figure 6 (e) Radiation pattern (Gain total) of the antenna for phi 280˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
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Figure 6 (f) Radiation pattern (Gain total) of the antenna for phi 350˚ (i) Design 1 (conventional
material) (ii) Design 2 (DNG material)
Figure 6 shows a comparison of radiation pattern (gain) for conventional material and DNG
material for different phi cuts. Figure 6 (a-f) shows the radiation pattern for both conventional
material design and DNG material design for phi 0˚, 70˚, 140˚, 210˚, 280˚ and 350˚ respectively.
As shown in the figure the gain for the DNG material for all the phi cuts is almost same and with
good directivity while that of the conventional material is not same for different phi cuts and its
directivity is also not good. As shown in the figure the radiation is good for the DNG material
design compared to the conventional material design. Table 3 shows the gain improvement for
different phi cuts. It is clear from the table that DNG material design gives 10 to 12 times more
improvement compare to the conventional material design
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Table 3. Gain improvement for different phi cuts
Phi
Maximum Gain
(Conventional
Material)
Maximum Gain
(DNG Material)
Improvement
(%)
0˚
0.048
0.582
1212
70˚
0.048
0.582
1212
140˚
0.059
0.582
986
210˚
0.048
0.585
1218
280˚
0.048
0.582
1212
350˚
0.049
0.582
1187
Thus comparing the polar plot and the radiation pattern of gain for the two designs we can
observe that the design with DNG material is better over the conventional material.
4. CONCLUSION
We have carried out the theoretical-geometric investigations, analysis, design, modeling and
iterative simulations for center frequency of 1.25 GHz. Results for VSWR, return loss, radiation
pattern and polar plot have been simulated for both the designs . Comparing the two designs, the
design with DNG material shows good response over conventional material. Here the radiation
pattern (gain) of the antenna has been enhanced by DNG material design 10 times more
compared to conventional material design. The VSWR and the return loss of the DNG material
design is also better compared to the conventional material design. For both the designs we are
getting three bands so the antenna can be used for several wireless applications in UHF and L
band communication. Here we have got triband designs, by truncating the design and adding
multiple split ring resonators we can improve the design further.
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