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All content in this area was uploaded by Kalyan Sundar Kola on Mar 16, 2021
Content may be subject to copyright.
A Printed Array of High-gain Fractal Antennas for
X-band Applications
Kalyan Sundar Kola
Dept. of Electronics &Communication Engineering
National Institute of Technology Goa, Goa,India.
E-mail:kalyankola12@gmail.com
Anirban Chatterjee
Dept. of Electronics &Communication Engineering
National Institute of Technology Goa, Goa,India.
E-mail:snanirban@nitgoa.ac.in
Abstract—A 1×2printed linear array of microstrip fractal
antennas has been reported in this article. The proposed single
element antenna is designed to operate in X-band with the
center frequency (fr) of 10.00 GHz. The proposed structure
is obtained by etching the Minkowski boxes in all the four
corners of a square geometry. In the next step, a 50% scaling
factor is applied to each Minkowski square boxes of the resultant
geometry. Further, the four-folded and centrosymmetric structure
has been proposed to achieve symmetric radiation pattern in a
particular direction. A two-element linear array with Wilkinson
equal power divider has been designed to obtain more improved
parametric results for the application of wireless communication
in X-band. The single element and the array maintains a gain of
11.46 and 14.24 dBi respectively. Both antenna gives a low cross-
polarization level of −46.35 and −39.58 dB respectively without
tampering the ground plane i.e., the novelty of the proposed
design. The radiation efficiency, the computed aperture efficiency,
and the front-to-back ratio (FBR) of the structures are quite
acceptable for X-band wireless communication.
Index Terms—Antenna array, fractal antenna, microstrip
patch, Minkowski, Wilkinson power divider, X-band.
I. INTRODUCTION
The allotted X-band spectrum is dedicated to providing
such important applications as mobile satellite, fixed satellite,
radiolocation, navigation, wireless communication, etc. Apart
from that, to identify any target properly with a high-resolution
image, the X-band is preferable to use for its short-wavelength
[1] property. This band is also dedicated to private and
government surveillance applications like weather monitoring,
air traffic control, maritime vessel traffic control, defense
tracking and vehicle speed detection for law enforcement, etc.
For future wireless device versatility, high gain, and good
radiation efficiency are the major factors for the applicability
of the antenna. The high gain antenna is mostly demanding
because the low-gain antenna gives a lower grade of service
which is not acceptable for X-band communication. The
microstrip patch antenna [1], [2] with high-gain is a good
candidate for those purposes because of its extra features like
lightweight, less size, easy to fabricate, and easy to interface
with the other devices. Therefore, the author proposed a linear
array of hybrid-fractal antennas where the single antenna was
structured by two times implementation of Minkowski 1st
iteration and applying a 50% scaling factor on the resultant
geometry in between them respectively.
In literature [3], a method of selecting the substrate material
to design the patch antenna for a different frequency of
operation is addressed by Carver et al. The advanced features
and the advantages of the patch antenna and the array for
communication have been investigated by Pozar et al [4].
To design an antenna or array, the rapidly growing demands
of fractal geometry has been expressed by Douglas et al
[5]. Author et al [5] also stated that the incorporation of
fractal geometry is useful to design an application-oriented
re-configurable systems. To resonate with any antenna at the
desired frequency, the importance of the slots in the ground
plane of the structure has been reported by Latif et al [6].
The importance of fractal structure for the antenna used in
modern communication systems is addressed by Krzysztofik
et al [7]. The X-band application-oriented, an iris loaded,
broad-wall rectangular waveguide, cross-dipole slot-antenna
has been reported by Ghatak et al [8]. Samsuzzaman et al [9]
reported a S-shaped multi-frequency patch antenna for X-band
applications. The important role of U-slot in the radiating
part of an antenna to achieve improved impedance bandwidth
is investigated by Deshmukh et al [10]. Srivastav et al [11]
proposed a X-band application oriented differential substrate
integrated with good common-mode suppression and high
gain waveguide antenna. An L-slot and circular split-ring
resonator (SRR) ground plane based Sierpinski triangle-shaped
antenna for wireless communication has been presented by
Ali et al [12]. A miniaturized, co-planar waveguide-fed, on-
chip monopole antenna which is capable to avoid the X-band
interference in up-link satellite communication is reported by
Mandal et al [13]. X-band application-oriented a leaf-shaped,
co-planar waveguide(CPW) fed, triple-notched, ultra wideband
antenna is proposed by Kundu et al [14].
Wilkinson et al [15] describes the procedure of an N-way
power divider network design which may use to construct
a uniform antenna array. A wideband communication-based
array with U-shaped slotted microstrip patch antenna is ad-
dressed by Wang et al [16]. A next-generation wireless and
satellite-based application-oriented triple-band, 1×2and 1×4
microstrip array antenna has been proposed by Razzaqi et al
[17]. A cross-polarized and wideband array with differential
fed-patch is designed by Jin et al [18]. A miniaturized and
frequency selective surface with effective shielded antenna for
X-band coomunication is reported by Nauman et al [19]. Jin et
2020 International Conference on Communication, Computing and Industry 4.0 (C2I4) | 978-1-7281-8312-1/20/$31.00 ©2020 IEEE | DOI: 10.1109/C2I451079.2020.9368946
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A B C
E
step-1 step-2
step-3
step-4
Minkowski
1st iteration
50% scaled
4-quadrant
topology
4-folded centro
symmetric topology
D
(a) (b) (c)
(d)(e)
x
y
x'
y'
x
y
x'
y'
a
a/3 a/6
a/3
a/12
Fig. 1. (a)-(e) step-wise formation of proposed fractal geometry.
al [20] proposed a multi-layered antenna with differential-fed,
used to achieve enhanced bandwidth for X-band communica-
tion. In X-band, the wireless communication-oriented linear
array of nature-inspired Clover-leaf shaped microstrip fractal
patch antennas is reported in [21] .
The step-wise formation, the complete embodiment, calcula-
tion of fractal-length, and computation of the radiating area of
the proposed single element are described in Section II. The
design of a three-port matching network and the configuration
of the proposed array are addressed in Section III. The
simulated results of the proposed antennas have been reported
in Section IV. Section V concludes the discussions.
II. DE SI GN O F TH E AN TE NNA
The pictorial representation of the step-wise formation of
the proposed fractal structure has been presented in Fig.1 (a)-
(e). The square geometry Awith side length of aas shown in
Fig.1 (a) has been considered as initial structure. Due to having
the symmetrical view property, the square geometry is consid-
ered as the initial structure to design the fractal geometry on
it. In the first step, a square box, obtained from Minkowski 1st
iteration, has been etched from all the four corners of a square,
denoted by Aas shown in Fig.1(a). The resultant geometry
is shown in Fig.1(b) and is denoted by Bwhose side length
becomes a/3. In the next step, another square box has been
etched from the center of the remaining square edge of Band
the resultant structure Cis depicted in Fig.1(c). The length
of the etched square in step-2is obtained by imposing a scale
factor of 50% of any one of the edge square of Band resultant
of step-2is denoted by C. In order to achieve symmetric
radiation pattern from the structure, a four-quadrant topology
has been proposed in step-3. Using the proposed topology,
the one-quadrant geometry has been placed in the 4-quadrant
positions and obtained the four-folded fractal structure as D,
is the outcome of step-4which is reflected in Fig.1 (d). In
order to achieve improved parametric results, a four-folded
and centrosymmetric topology has been considered. Due to
this, the one-quadrant geometry Cis placed at the center of
Dand achieved the resultant final proposed structure Ewhich
LF
LP
WP
LS
WS
PORT
x
y
z
Fig. 2. Proposed fractal patch antenna.
TABLE I
DETAI LE D DIMENSION OF PROPOSED ANTENNA
Symbol mm Symbol mm Symbol mm
a14.00 WS56.00 LS56.00
WP28.00 LP28.00 LF18.66
is depicted in Fig.1 (e). The proposed design is obtained by
implementing the Minkowski 1st iteration method followed by
applying 50% scaling factor on each Minkowski square boxes
of modified resultant structure respectively. This is the novelty
of this design. The numeric value of the used notations of Fig.1
are mentioned in TABLE I.
A. Computation of fractal length
Due to the implementation of fractal geometry, the overall
fractal length has been enhanced and it becomes more than
the conventional length of the proposed microstrip patch. The
dimensions of the proposed geometry in terms of length are
depicted in Fig.2 and the numerical values are enlisted in
TABLE I.
The length of the non-fractal square geometry (CL) is as
follows:
CL= 8 ×a(1)
The fractal length FLB of the geometry Bobtained from
Fig.1(b) is as follows:
FLB = 12 ×a
3(2)
Similarly, the fractal length FLC of Ci.e., the one-quadrant
of the proposed structure is obtained from Fig.1(c) as follows:
FLC =FLB + 12 ×a
6!+ 8×a
12!− 4×a
6!(3)
Hence, the total fractal length of the final geometry Eas shown
in Fig.1(e), is as follows:
FL= 5 ×FLC (4)
The enhanced fractal length (EL) becomes:
EL= FL−CL
CL!×100% (5)
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The length of non-fractal square geometry and the fractal
length of the proposed fractal structure obtained by referring
the Fig.2 and TABLE I, are 112.00 and 326.67 mm respec-
tively. Therefore, the effective fractal length is enhanced by
191.67% which ensures to achieve good parametric results
for the particular application in X-band.
B. Computation of radiating area
The fractal area (FA) of Bas shown in Fig.1 (b) is as
follows:
FB=a2− 4×a2
9!(6)
Similarly, the fractal area (FC) of Ci.e., one-quadrant of the
proposed geometry as shown in Fig.1 (c) is as follows:
FC=FB− 4×a2
36!(7)
Hence, the total fractal area of the final geometry Eas depicted
in Fig.1 (e) becomes:
Ft= 4 × FC+FC
4!(8)
The computed effective fractal area of the proposed antenna is
435.55 mm2which is used to radiate the EM wave at desired
frequency in particular direction.
C. Complete embodiment
The proposed quadrantal and centrosymmetric structure E,
obtained as an outcome of step-4, is placed at the top layer
of the Roger RT Duroid 5880 (r= 2.2and loss tangent
0.0009) substrate material whereas the bottom layer is working
as a conducting ground layer. The thickness of the substrate
(hs) layer and the copper layer (ht) are 0.787 and 0.017 mm
respectively. The complete embodiment is shown in Fig.2. LF
is the feedline which is used to derive the power from the
source port to the patch which yield helps to radiate EM wave
properly in the desired direction. The detailed dimensions of
the proposed single element are enlisted in TABLE I.
III. DESIGN OF ANT EN NA ARR AY
This section describes the construction of the three-way
power divider network and construction of the linear array
respectively.
A. Impedance matching network
A two-way power divider network [15] is shown in Fig. 3.
This network consists of two different kinds of transmission
lines whose impedance is Z0and √2Z0respectively. In the
Fig. 3, the transmission line with ‘orange’ color indicating the
Z0transmission line, and the line with ‘blue’ color indicating
√2Z0transmission line or quarter-wave transmission line
respectively. To achieve a perfec matching between source
and load, the length of the transmission line is considered
as integer multiple of λ/2or λ/4, where λis the free-space
wavelength. To reduce the power loss of the network, an
√2Z0λ/4
2Z0
Z0
Z0
Z0
PORT 1
PORT 3
PORT 2
Fig. 3. 3-port matching network.
x
y
z
K1
K2
K3
K4
R
L4
L5
L2L6
L1
L3
W50
W70
PORT
LA
WA
d
Fig. 4. Proposed 1×2antenna array.
TABLE II
DETAI LE D DIMENSION OF PROPOSED ANTENNA ARRAY
Symbol mm Symbol mm Symbol mm
WA98.00 LA71.00 L17.50
L20.50 L32.00 L45.08
L51.50 L69.48 K11.31
K21.00 K31.88 K41.50
W50 2.29 W70 1.31 R1.00
isolation resistor of 2Z0is mounted in the junction of quarter-
wave transmission lines. The width details of the two different
kinds of transmission lines are enlisted in TABLE II. In this
type of matching network, the derived power from Port 1
is equally distributed among the respective output ports i.e.,
Port 2and Port 3, which is depicted in Fig. 3. This kind of
matching network is designed by considering the principle of
Wilkinson power divider with equal magnitude [15].
Input impedance (Zin)of the transmission line can be
determined as [1]:
Zin =Z0
(ZL+jZ0tanβl)
(Z0+jZLtanβl)(9)
where ZLis load impedance, Z0is characteristic impedance
and βl is the transmission line length respectively.
B. Configuration of antenna array
A1×2linear array with an impedance matching network
is presented in Fig. 4. The Wilkinson power divider [15] is
incorporated to design the proposed array. For avoiding the
effect of mutual coupling, the antennas of the array are placed
with maintaining a 0.5λdistance between them. The source
power is delivered through L1to each of the antenna of the
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x
y
z
W50
W70
PORT
d
x
y
z
PORT
d
W50
W70
PORT
x
y
z
d
W50
W70
W50
PORT
x
y
z
d
W70
(a)
(b)
(c) (d)
Array-1 Array-2
Array-3
Proposed
Fig. 5. Comparison of array geometries:(a) Array-1,(b) Array-2,(c) Array-3
and (d) Proposed array.
TABLE III
COMPARATIVE PERFORMANCE OF THE DIFFERENT ARRAY GEOMETRIES
Caption Size[cm2]fr[GHz] S11 [dB] IBW [MHz] Gain [dBi] SLL[dB] η[%]
Array-1 70.56 9.92 −14.65 192 12.40 −10.26 81.50
Array-2 79.20 9.93 −18.825 254 12.10 −11.52 84.62
Array-3 79.22 9.91 −19.56 298 11.90 −12.36 82.98
Proposed 68.60 10.04 −20.52 324 14.20 −14.26 89.65
IBW →Impedance Bandwidth;SLL→Side-lobe level.
array via 70 Ω junction followed by 50 Ω transmission lines.
In Fig. 4, the notations L1to L6are used to define the sub-
length of 50 Ω transmission lines. The magnifying portion
of Fig. 4 represented the 70Ω transmission line whose sub-
length notations are indicated as Ki, where 1≤i≤4.
The overall length of 50 Ω and 70Ω transmission lines are
considered as integer multiple of λ/2and λ/4respectively.
An 100 Ω isolation resistor(R) is mounted in the junction
of the 70 Ω transmission lines as shown in the magnifying
portion of Fig. 4. The width and length of the proposed array
are indicated as WAand LArespectively. All the dimension
notations which are used to represent the array are enlisted in
TABLE II.
C. Structural analysis
Two-element array with different kind of feed-networks
are depicted in Fig. 5. A linear and a planar array with
conventional feed-network as Array-1and Array-2has been
shown in Fig. 5(a) and (b) receptively. Similarly, the Wilkinson
power divider network base designed a planar and a linear
array, named as Array-3and Proposed array, are presented
in Fig. 5(c) and (d) receptively. The simulated results related
comparative performance of all those arrays is presented in
TABLE III. From the TABLE III, it is clear to observe
that, the proposed array resonates at desired frequency and
gives better parametric results like minimum return loss, good
impedance bandwidth, high gain, lower side-lobe level and
better radiation efficiency compare to the other arrays of Fig. 5.
(a) (b)
(c) (d)
(e)
Fig. 6. Simulated results of antenna:(a)return-loss (b)gain and FBR (c)E and
H-field radiation patterns (d)2D radiation pattern (e)3D radiation pattern.
TABLE IV
PARA MET RI C PERFORMANCE OF ANTE NNA A ND AR RAY
Parameters Single element Array
Frequency [GHz] 10.00 10.04
S11 [dB] −26.14 −20.52
Bandwidth (MHz) 382 324
VSWR 1.10 1.21
Impedance[Ω]49.92 49.87
Absolute gain [dBi] 11.46 14.24
Directivity [dBi] 12.72 15.56
Front-to-back ratio [dB] 18.90 20.65
X-pol along main beam direction [dB] −46.35 −39.58
Aperture efficiency (ηap) [%]77.51 78.30
Radiation efficiency (η) [%]91.20 89.65
Therefore, the linear array designed with Wilkinson power
divider network is preferred for the X-band application and
the detailed simulation results are graphically presented in the
next section.
IV. RES ULT S AN D DISCUSSION
The proposed fractal antenna and 1×2array antenna have
been designed and simulated using SONNET and the parame-
ters are cross verified by Computer Simulation Technology-
Microwave Studio (CST-MW), version 2018. The detailed
parametric results of the proposed antennas are described as
follows.
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(a) (b)
(c) (d)
(e)
Fig. 7. Simulated results of array:(a) return-loss (b) gain and FBR (c) E and
H-field radiation patterns (d) 2D radiation pattern (e) 3D radiation pattern.
The simulated antenna parameters of the single antenna are
depicted in Fig.6. The characteristics of the return loss of the
antenna is graphically presented in Fig.6 (a), where the S11
and the impedance bandwidth are indicated as −26.14 dB and
382 MHz respectively at 10 GHz resonating frequency. The
obtained impedance bandwidth is to fulfill the bandwidth re-
quirement for X-band communication. The simulated absolute
gain and the front-to-back ratio (FBR) [22], [23] of the antenna
are shown in Fig.6 (b). The Fig.6 (b) indicates that the absolute
gain and the FBR of the antenna are very high and the values
are 11.46 dBi and 18.90 dB respectively. The simulated E- and
H-field characteristics of the antenna are recorded in Fig.6 (c).
The Fig.6 (c) shows that the obtained cross-polarized (X-pol)
field of the antenna is −46.35 dB which is reasonably very
low. This low X-pol level is achieved without tampering the
ground plane or implementing any kind of defective ground
structure (DGS) in the bottom plane of the antenna, which may
drift the desired resonating frequency and this is the novelty
of this design. The polar-plot of the radiation patterns of the
antenna for both xz and yz-plane are depicted in Fig.6 (d).
It has been clear to observe from Fig.6 (d) that, the back-
lobe radiation of the antenna is under the tolerance limit and
it is acceptable for X-band communication. The 3D radiation
pattern of the antenna has been shown in Fig.6 (e), from where
it is clear to observe that, the antenna is radiate symmetrically
at θ= 0◦direction it gives the maximum directivity. The
corresponding colored scale is indicating the radiating absolute
gain which is achieved from the design.
The aperture efficiency [24], [25] of antenna can be com-
puted as follows:
ηap =D
Dmax
(10)
Dmax =4πAs
λ2(11)
where Dand Dmax are the directivity and maximum direc-
tivity of the antenna, Asis the overall surface area of antenna
including substrate, and λis free-space wavelength.
The simulated directivity of the antenna is 12.72 dBi and the
area of the patch is of 56.00×56.00 mm2. Hence, the aperture
efficiency(ηap) of the antenna is 77.51% which is quite good
and acceptable for the desired application. The radiation
efficiency(η) of the antenna is 91.20% which is reasonably
high and useful for the application of wireless communication.
The VSWR and the impedance of the antenna are 1.10 and
49.92 Ω respectively. All the simulated parameters of the
single antenna are enlisted in TABLE IV.
The antenna parameters of the proposed array have been
analyzed and the simulated results are graphically presented in
Fig. 7. The characteristic of return-loss of the array is depicted
in Fig.7 (a). The S11 and the corresponding impedance band-
width are achieved as −20.52 dB and 324 MHz respectively
at 10.04 GHz resonating frequency. The obtained impedance
bandwidth is acceptable for wireless communication in X-
band. The absolute gain and the FBR [22], [23] of the proposed
array are also high and the simulated values are of 14.24 dBi
and 20.65 dB respectively, which has been reflected in the
Fig.7 (b). The characteristics of E- and H-field of the array has
been depicted in Fig.7 (c). Without implementing any kind of
DGS structure in the bottom layer of the array, it gives a very
low cross-polarization level and the value is −39.58 dB which
is the novelty of the design. The polar-radiation patterns of the
array for both xz and yz-plane are depicted in Fig.7 (d). It is
also shown that the array gives the maximum directive gain
in the θ= 0◦direction for both planes. The 3-dimensional
pattern of radiation of the array has been depicted in Fig.7 (e),
which indicates that the array radiates symmetrically in a sin-
gle direction. The right-handed scale of the Fig.7 (e) indicating
the magnitude of the simulated absolute gain achieved from the
designed array. The simulated directivity of the antenna array
is 15.56 dBi and the area of the patch is 98.00 ×71.00 mm2.
Hence, the aperture efficiency(ηap) of the array is 78.30%
which is acceptable for this particular application in X-band.
The radiation efficiency(η) of the antenna array is 89.65%
which is reasonably high and also acceptable for wireless
communication. The VSWR and the impedance of the array
are 1.21 and 49.87 Ω respectively. All the simulated antenna
array parameters are enlisted in TABLE IV.
V. CONCLUSION
The Minkowski method oriented fractal antenna, the 1×2
linear array antenna, and their parametric behaviors for X-band
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application have been investigated. The proposed fractal an-
tenna is designed to achieve high gain, low-cross polarized EM
wave, and high radiation efficiency. The low cross-polarized
EM wave has been achieved from the antenna without tem-
pering the ground plane or implementing any DGS technique
in the ground plane, which is the novelty of the proposed
design. The linearly polarized array antenna also maintaining
good return loss characteristics along with symmetric radiation
pattern in the particular direction of radiation. The proposed
array gives a high gain, low cross-polarization level along
the main bean direction and it also provides good radiation
efficiency. Both antenna provides more than 77% of aperture
efficiency which reflects the good sound of design. For both
the cases, the output impedance is more than 49Ω, which
stated the perfection of matching between source and load. The
single antenna and the array, both are fulfilling the minimum
requirements for X-band wireless communication. The better
parametric results can be achieved by increasing the number
of antennas in the array geometry with the consideration of a
perfect and compact matching network.
ACKNOWLEDGMENT
Authors would like to thanks for the project titled “De-
sign of Compact Shaped Beam Antenna Array for Ded-
icated Short Range Communication Service” (File No.:
SB/S3/EECE/226/2016), SERB Extra Mural Research Fund-
ing, Government of India.
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