Md. M. ISLAM et al.: EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A -SHAPED MICROSTRIP ANTENNA
33–37
EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A
-SHAPED MICROSTRIP ANTENNA
VPLIV Z VLAKNI OJA^ANE EPOKSI PODLAGE PRI -OBLIKI
MIKROTRAKASTE ANTENE
Md. Moinul Islam1, Mohammad R. I. Faruque1, Mohammad Tariqul Islam2,
Haslina Arshad3
1Centre for Space Science (ANGKASA), Kompleks Penyelidikan Building, Universiti Kebangsaan, Malaysia
2Department of Electrical, Electronic & Systems Engineering, Universiti Kebangsaan, Malaysia
3Centre of Artificial Intelligence Technology, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor D. E., Malaysia
mmoiislam@yahoo.com; rashedgen@yahoo.com; titareq@yahoo.com; has@ftsm.ukm.my
Prejem rokopisa – received: 2014-08-18; sprejem za objavo – accepted for publication: 2015-03-09
doi:10.17222/mit.2014.206
A -shaped microstrip antenna using an epoxy-resin-fibre substrate is presented. The proposed antenna consists of a circular
slot and two rectangular slots printed on a dielectric resin-fibre substrate and is excited by a 50- microstrip transmission line.
A commercially available, high-frequency structural simulator (HFSS) based on the finite-element method (FEM) was used in
this investigation. The nearly omni-directional and bidirectional radiation pattern exhibited average gains of 3.12 dBi and 5.44
dBi for the lower band and upper band, respectively. The effects of epoxy-resin-fiber are discussed through comparisons of
different substrate materials.
Keywords: epoxy resin-fibre, microstrip line, -shaped
Predstavljena je mikrotrakasta antena -oblike na epoksi podlagi, oja~ani z vlakni. Predlagana antena sestoji iz kro`ne re`e in
dveh pravokotnih re`, natiskanih na dielektri~ni podlagi iz smole z vlakni in sta vzbujani s 50  mikrotrakastim vodnikom. V tej
preiskavi je bil uporabljen komercialno razpolo`ljiv visoko frekven~ni strukturni simulator (HFSS), ki temelji na metodi
kon~nih elementov (FEM).V spodnjem in zgornjem pasu je vsesmerno sevanje kazalo 3,12 dBi, dvosmerno sevanje pa 5,44 dBi.
Vpliv vlaken za oja~anje je bil prikazan s primerjavo razli~nih materialov podlage.
Klju~ne besede: vlakna za oja~anje epoksija, mikrotrakasta linija, -oblika
1 INTRODUCTION
The microstrip patch antenna plays an important role
as a harbinger in wireless communication systems and is
now being used to address the changing demands of
future antenna technology. The microstrip patch antenna
has been extensively used in wireless communication
systems, because they are conformal, have a low profile,
are easy to fabricate with integrated circuits (ICs), and
enable easy integration with array and electronic compo-
nents. Many researchers have an interest in designing
microstrip antennas and still face a major challenge to
implement these applications. Currently, various types of
antennas have been proposed to face the increasing
requirements for a modern bearable wireless communi-
cation device that has the capability of consolidating
more than one communication system into a single
module.1–6
In7, a rectangular slot antenna was proposed for
dual-frequency operation. Su et al.8 presented a printed
dipole antenna using U-slot arms to enable dual-band
operation. Suh and Chang9 reported a low-cost micro-
strip dipole antenna for wireless communications. In10, a
PIFA antenna with a U-slot was presented for dual-band
operation. Lin et al.11 mentioned a dual-loop antenna for
use with a 2.4/5 GHz Wireless LAN. A monopole an-
tenna with double-T was presented in12 for 2.4/5.2-GHz
WLAN operations. A planar antenna was investigated
with bandwidth enhancement for X-band applications13.
An E-shaped patch antenna of wideband circularly
polarized was presented for wireless applications14. A
Compact 5.5-GHz Band-Rejected UWB Antenna was
proposed using Complementary Split Ring Resonators15.
A new double L-shaped multiband patch antenna was
presented on a polymer resin material substrate16.
In this study, a -shaped microstrip antenna was
designed on a 1.6-mm-thick epoxy-resin-fibre substrate
material. The downlink frequency range is from 4.74
GHz to 4.87 GHz and the uplink frequency range is from
8.42 GHz to 8.73 GHz. The results will be discussed in
detail with a parametric study.
2 ANTENNA GEOMETRY AND PARAMETRIC
STUDY
High-Frequency Structure Simulator (HFSS), a com-
mercially available Ansoft package, is a powerful and
efficient three-dimensional (3D) full-wave simulation
software that solves EM equations through the sub-
division of a large problem into easy constituent units
Materiali in tehnologije / Materials and technology 50 (2016) 1, 33–37 33
UDK 66.017:678.686 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(1)33(2016)
and then consolidating the solution as a matrix of
simultaneous equations for the complete problem space,
which provides a numerical solution to Maxwell’s
equations using the FEM. Hence, HFSS was used in this
study.
The geometry of the proposed antenna is shown in
Figure 1. The antenna comprises three conducting slots
on the patch and two on the ground. A circular slot and
two similar lateral rectangular slots are on the patch and
two rectangular slots are on the ground of the proposed
antenna. The two rectangular slots are of equal length LP
and width WP. R is the radius of the circular slot. The
design procedure begins with the radiating patch, along
with the substrate, the ground plane and a feed line. The
antenna was printed on a FR4 substrate with 1.6 mm in
thickness that exhibits a relative permittivity of 4.60, a
relative permeability of 1, and a dielectric loss tangent of
0.02. One circular slot and two rectangular slots are cut
from the rectangular copper patch. Another two
rectangular slots are also cut from the ground plane. In
this manner, the proposed slotted circle patch antenna is
produced. Two resonant frequencies of 4.51 GHz and
8.35 GHz are obtained by adjusting the length and width
of the slots of the proposed antenna. Here, a microstrip
line is used to feed the RF signal into the proposed
antenna. The Sub Miniature version A (SMA) connector
is used at the end of antenna feeding line for the input
RF signal.
Finally, the optimal dimensions were determined as
follows: L = 40 mm, Lp = 12 mm, Lg = 40 mm, Ls = 4
mm, R = 12 mm, W = 40 mm, Wp = 4 mm, Wg = 40 mm,
Ml =17 mm, and Mw = 6 mm.
The epoxy-resin-fibre consists of reinforcing insula-
tion material. There are various types of epoxy-resin-
fibre material for use as an antenna substrate. In this
study, we have used FR4 as the epoxy-resin-fibre sub-
strate material that is impregnated with thermoset resin.
FR4 has superior mechanical and dielectric properties,
good moisture/heat resistance, stable electrical perfor-
mance at high temperature, good flatness and a smooth
surface. FR4 is widely used to produce printed-circuit
boards (PCBs).
The length, width, VSWR, return loss of the patch
antenna can be calculated from Equations (1) to (6)
presented in17, where L and W are the length and width
of the patch, respectively, c is the velocity of light, r is
the dielectric constant of substrate, h is the thickness of
the substrate, f0 is the target centre frequency, e is the
effective dielectric constant and  is the radiation
coefficient:
W
c
f
=
+
2
1
20
 r
(1)
L
c
f
l= −
2
2
0  r
Δ (2)
  e r r= + + − +
⎛
⎝
⎜ ⎞
⎠
⎟1
2
1
1
2
1 1
10
( ) ( )
h
W
(3)
Δl h
W h
W h
=
+ +
− +
0 412
03 08
0 258 08
.
( . )( / . )
( . )( / . )


e
e
(4)
VSWR =
+
−
1
1


(5)
Return loss = −
⎛
⎝
⎜
⎞
⎠
⎟10
1
lg

(6)
Md. M. ISLAM et al.: EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A -SHAPED MICROSTRIP ANTENNA
34 Materiali in tehnologije / Materials and technology 50 (2016) 1, 33–37
Figure 2: Return loss of simulation using different substrate materials
Slika 2: Povratne izgube pri simulaciji z uporabo razli~nih materialov
podlage
Figure 1: Proposed antenna: a) top view and b) bottom view
Slika 1: Predlagana antena: a) pogled iz vrha in b) pogled iz dna
Table 1: Dielectric properties of the different substrates
Tabela 1: Dielektri~ne lastnosti razli~nih podlag
Material Permittivity Loss Tangent
Teflon (tm) 2.1 0.01
RT/Duroid 5870 2.33 0.0023
Epoxy resin-fiber (Proposed) 4.66 0.02
Al2O3 9.8 0.0009
RT/Duroid 6010 10.2 0.0023
The return losses determined by the simulation using
different substrate materials are shown in Figure 2. No
resonance was found on the lower band when we used
the high-permittivity materials of Duroid 6010, and
Al2O3 ceramic and the low permittivity materials of
Duroid 5870, and Teflon as a substrate. Finally, FR4 was
used in the proposed design as the epoxy-resin-fiber
substrate material and two strong resonances were
achieved, with the desired bandwidth and high gain. The
10-dB bandwidths of 130 MHz from 4.74 GHz to 4.87
GHz and of 310 MHz from 8.42 GHz to 8.73 GHz were
achieved. The dielectric properties of the materials are
listed in Table 1.
A parametric study was performed to observe the
effects of the proposed antenna parameters. In particular,
the effects of the different parameters on the return loss
were observed.
Figure 3 shows the return loss of the simulation for
different values of R. The simulation includes L = 40 mm,
Lp = 12 mm, Lg = 40 mm, Ls = 4 mm, W = 40 mm, Wp =
4 mm, Wg = 40 mm, Ml = 17 mm, and Mw = 6 mm with
the different values of R. The graph indicates that better
coupling is obtained for the upper band using the value
of radius as 11 mm and 13 mm. By using R = 12 mm, the
desired dual-band operation was obtained, with a better
coupling on both the lower and upper bands.
The return loss of the simulation for different values
of Ml is shown in Figure 4. The simulation includes L =
40 mm, Lp = 12 mm, Lg = 40 mm, Ls = 4 mm, R = 12
mm, W = 40 mm, Wp = 4 mm, Wg = 40 mm and Mw = 6
mm with Ml. The results presented in the graph clearly
indicate that improved coupling was achieved at the
upper band when using the value of Ml as 40 mm. As a
result, the optimized value is 40 mm.
Figure 5 shows the return loss simulation for diffe-
rent values of Mw. The simulation includes L = 40 mm,
Lp = 12 mm, Lg = 40 mm, Ls = 4 mm, R = 12 mm, W = 40
mm, Wp = 4 mm, Wg = 40 mm, Ml =17 mm, and with the
different values of Mw. The width of the microstrip line
has a greater effect on the coupling for both the lower-
and upper-band frequencies. This coupling can be
achieved when Mw is 6 mm.
3 RESULTS AND DISCUSSION
The gain of the proposed antenna is shown in Figure
6. An average gain of 3.12 dBi is achieved with the first
resonance of 4.80 GHz and 5.44 dBi is achieved with the
second resonance of 8.57 GHz. In addition, the gain for
the upper band is greater than that for the lower band.
Figure 7 shows the radiation efficiency of the proposed
Md. M. ISLAM et al.: EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A -SHAPED MICROSTRIP ANTENNA
Materiali in tehnologije / Materials and technology 50 (2016) 1, 33–37 35
Figure 5: Return loss of the simulation using different values of Mw
Slika 5: Povratne izgube pri simulaciji z uporabo razli~nih vrednosti
Mw
Figure 3: Return loss of the simulation using different values of R
Slika 3: Povratne izgube pri simulaciji z uporabo razli~nih vrednosti R
Figure 4: Return loss of the simulation using different values of Ml
Slika 4: Povratne izgube pri simulaciji z uporabo razli~nih vrednosti Ml
antenna. The average lower-band efficiency is 75.18 %
and the higher-band efficiency is 81.35 %, i.e., the
lower-band radiation efficiency is smaller than the
higher-band efficiency.
The radiation pattern of the proposed antenna is
shown in Figure 8 for: a) 4.80 GHz at the E-plane, b)
4.80 GHz at the H-plane, c) 8.57 GHz at the E-plane, d)
8.57 GHz at the H-plane. The E and E	 fields indicate
the cross-polar and co-polar components, respectively.
The effect of cross-polarization in the radiation pattern is
due to the lower microstrip antenna. The cross
polarization effect is higher in the H-plane for both
resonances. When the frequency increases, the effect
increases, enabling simple interpretation from the
radiation pattern. Moreover, nearly omni-directional and
symmetrical radiation patterns were attained along both
the E-plane and the H-plane. The same radiation pattern
was found to exist over the C and X-bands. The obtained
radiation patterns indicate that the proposed antenna
delivers linear polarization, where the level of
cross-polarization is lower than that of the
co-polarization in all of the simulated radiation patterns.
When the radiation pattern of a microstrip antenna is
symmetric and omni-directional, it provides some
reasonable benefits. One benefit is that the resonance
does not shift for different directions, so a large amount
of stable power is in the direction of the broadside beam.
Another advantage is that the radiation pattern is more
reliable on the operational bands.
Figure 9 shows the current distribution of the pro-
posed antenna for: a) 4.51 GHz and b) 8.35 GHz. A large
amount of current flows through the feeding line. The
Md. M. ISLAM et al.: EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A -SHAPED MICROSTRIP ANTENNA
36 Materiali in tehnologije / Materials and technology 50 (2016) 1, 33–37
Figure 9: Current distribution at: a) 4.80 GHz and b) 8.57 GHz
Slika 9: Razporeditev toka pri: a) 4,80 GHz in b) 8,57 GHz
Figure 7: Radiation efficiency of the proposed antenna
Slika 7: U~inkovitost sevanja predlagane antene
Figure 8: Radiation pattern of the proposed antenna: a) 4.80 GHz at
the E-plane, b) 4.80 GHz at the H-plane, c) 8.57 GHz at the E-plane
and d) 8.57 GHz at the H-plane
Slika 8: Sevalni diagram predlagane antene: a) 4,80 GHz v ravnini E,
b) 4,80 GHz v ravnini H, c) 8,57 GHz v ravnini E in d) 8,57 GHz v
ravnini H
Figure 6: Gain of the proposed antenna
Slika 6: Izkoristek predlagane antene
electric field was initiated at this point. The current
distribution is more stable in the lower band than in the
upper band. The creation of the electric field near the
slots is reasonable. As a result, the excitation is strong
over all parts of the antenna for both the lower and upper
bands.
4 CONCLUSION
A -shaped microstrip antenna using an epoxy-
resin-fibre substrate was proposed in this paper. A simple
-shaped patch was proposed to miniaturize the antenna
and to obtain a new operating band resonant mode. An
antenna structure was designed, simulated and finally
characterized. The -shaped resonator, compact size,
stable nearly omni-directional and directional radiation
patterns, low cross-polarization, and efficiency with
improved bandwidth and higher gain make the proposed
-shaped dual band antenna a candidate for use in
C-band and X-band applications.
Acknowledgements
This work was supported by Universiti Kebangsaan
Malaysia under grant, Arus Perdana, No. AP-2013-011.
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Md. M. ISLAM et al.: EFFECTS OF AN EPOXY-RESIN-FIBER SUBSTRATE FOR A -SHAPED MICROSTRIP ANTENNA
Materiali in tehnologije / Materials and technology 50 (2016) 1, 33–37 37