Bandwidth and Gain Enhancement of MIMO Antenna by Using Ring and Circular Parasitic with Air-Gap Microstrip Structure

TELKOMNIKA, Vol.15, No.3, September 2017, pp. 1155~1163
ISSN: 1693-6930, accredited A by DIKTI, Decree No: 58/DIKTI/Kep/2013
DOI: 10.12928/TELKOMNIKA.v15i3.6377  1155
Received May 4 2017; Revised August 2, 2017; Accepted August 17, 2017
Bandwidth and Gain Enhancement of MIMO Antenna by
Using Ring and Circular Parasitic with Air-Gap
Microstrip Structure
Teguh Firmansyah*1
, Herudin2
, Suhendar3
, Romi Wiryadinata4
, M. Iman Santoso5
,
Yus Rama Denny6
, Toto Supriyanto7
1,2,3,4,5
Department of Electrical Engineering, University of Sultan Ageng Tirtayasa, Cilegon 42435
6
Department of Physics Education, University of Sultan Ageng Tirtayasa, Serang 42124
7
Department of Electrical Engineering, Jakarta State Polytechnic, Depok 16424
*Corresponding author, e-mail: teguhfirmansyah@untirta.ac.id
Abstract
This research was proposed a circular patch MIMO antenna by using a ring and circular parasitic
radiator structure. As a novelty, in order to enhance bandwidth and gain of circular patch MIMO antenna, a
conventional circular patch MIMO antenna will be added a ring and a circular parasitic. Therefore, this
research was investigated a conventional MIMO antenna (C-MA), ring parasitic MIMO antenna (RP-MA),
and circular parasitic MIMO antenna (CP-MA) as Model 1, Model 2, and Model 3, respectively. This MIMO
antenna was designed on FR4 microstrip substrate with r= 4.4, thickness h=1.6 mm, and tan = 0.0265.
This MIMO antenna has center frequency 2.35 GHz which is a frequency band for LTE application in
Indonesia. An Advance Design System (ADS) software was used to determine the antenna parameters.
The MIMO antenna C-MA / RP-MA/ CP-MA achieves 2.36GHz/ 2.38GHz/ 2.38 GHz, 70 MHz/ 100 MHz/
120 MHz, 1.625 dBi/ 4.066 dBi/ 4.117 dBi, 6.414 dBi/ 7.26 dBi/ 7.153 dBi, 33.9 %/ 47.8 %/ 49.70 %, -12.35
dB/ -22.21 dB/ -23.66 dB, and -30.924 dB/ -28.46 dB/ -27.59 dB for center frequency, bandwidth, gain,
directivity, efficiency, reflection coefficient, and mutual coupling, respectively. Compared to C-MA (Model1)
performances, The result showed that proposed antenna has wider-bandwidth/ higher-gain with 42.8%/
150.2 %, and 71.4%/ 163.3% for RP-MA (Model 2) and CP-MA (Model 3), respectively. The proposed
antenna has size of 50 mm x 130 mm x 23.2 mm. Measured results are in a good agreement with the
simulated results.
Keywords: Antenna, MIMO, ring parasitic, circular parasitic
Copyright © 2017 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
A Long Term Evolution (LTE) technology was developed to provide the requirement of
wireless data access with high bit-rate [1, 2]. The LTE technology uses a Multiple Input Multiple
Output (MIMO) antenna system [3-5]. Antennas based on microstrip technology are popularly
used because it has many benefits such as low cost, low profile, ease fabrication, and compact
[6, 7]. However, the microstrip antenna has disadvantages such as narrow bandwidth and low
gain [8, 9]. There are some attractive methods frequently used to enhance bandwidth and gain
such as microstrip-slot [10-12], microstrip notch [13], and parasitic air gap [14-19]. The research
which proposed by [10], [12-13] increases the bandwidth of the antenna, without gain
enhancement. Some antenna mentioned above still a relatively complex geometry. A parasitic
gap method which proposed by [14-19] are an excellent method. That method was not only to
increase bandwidth but also enhance a gain. Unfortunately, these studies are only applied to a
single patch antenna, not a MIMO antenna. MIMO antenna system is considered not only a
bandwidth, and a gain but also a mutual coupling. A frequently used method to reduce a mutual
coupling such as defected ground structure (DGS) [20], Electromagnetic band gap (EBG) [21],
and Metamaterial mushroom structures. These methods made more complicated designs of
MIMO antenna.
As a novelty, this research proposed a circular patch MIMO. In order to enhance
bandwidth and gain, a conventional circular patch MIMO antenna will be added a ring and a
circular parasitic radiator structure. Therefore, generally this research was investigated a
conventional MIMO antenna (C-MA), ring parasitic MIMO antenna (RP-MA), and circular

 ISSN: 1693-6930
TELKOMNIKA Vol. 15, No. 3, September 2017 : 1155 – 1163
1156
parasitic MIMO antenna (CP-MA) as Model 1, Model 2, and Model 3, respectively. This MIMO
antenna was designed on FR4 microstrip substrate with r= 4.4, thickness h=1.6 mm, and tan
= 0.0265. This MIMO antenna has center frequency of 2.35 GHz, which is a frequency band
for LTE application in Indonesia. A performance of MIMO antenna will be investigated include
center frequency, bandwidth, gain, directivity, efficiency, reflection coefficient, and mutual
coupling. The design of methodology was detailed in the following sections. Section 2 describes
the design of a circular patch MIMO antenna by using a ring and circular parasitic radiator
structure. The simulation was described in Section 3, and the measurement results of the MIMO
antenna was described in Section 4. Finally, Section 4 concludes this research.
2. Research Method
This part discusses some methods to conduct the research. Figure 1(a) shows a
circular patch conventional MIMO antenna (C-MA) [Model 1]. Figure 1(b) shows circular patch
MIMO antenna with a ring-parasitic substrate (RP-MA) [Model 2]. Furthermore, Figure 1(c)
shows circular patch MIMO antenna with a circular-parasitic substrate (CP-MA) [Model 3].
(a)
(b) (c)
Figure 1. (a) Coventional MIMO antenna (C-MA) [Model 1], (b) MIMO antenna with ring parasitic
substrate (RP-MA) [Model 2], (c) MIMO antenna with circular parasitic subtstrate
(CP-MA) [Model 3]
The radius of circular patch microstip antenna is given by [22]:
(1)
Where,
(2)
With h = thickness of substrate (cm) and fr = resonant frequency (Hz).
In this research, a direct feeding method was used. The relationship between width-
thickness (W/h) ratio of the feeding size and the value of Zo and the constant dielectric εr can be
obtained by Equation (3) [23-25]:

TELKOMNIKA ISSN: 1693-6930 
Bandwidth and Gain Enhancement of MIMO Antenna by using Ring and… (Teguh Firmansyah)
1157
(3)
Where:
(4)
(5)
Furthermore, the Zo can be determined by the ratio of width and thickness (W/h) [23-27]:
(6)
where:
(7)
This MIMO antenna was designed on FR4 microstrip substrate with r= 4.4, thickness
h=1.6 mm, and tan = 0.0265. An Advance Design System (ADS) software was used to
determine the antenna parameters. Figure 2(a) shows the extracted reflection coefficient and
mutual coupling values with varied R2. The chart shows that the reflection coefficient can be
tuned by modifying R2. It also can be seen that the mutual coupling values are still below -20 dB
for all values of R2. Furthermore, Figure 2(b) shows the extarcted reflection coefficient and
mutual coupling values with varied RP. It shows that RP only significant affect to reflection
coefficient, with less effect on mutual coupling.
(a) (b)
Figure 2. (a) The extracted reflection coefficient and mutual coupling values with varied R2; (b)
The extracted reflection coefficient and mutual coupling values with varied RP
Figure 3(a) shows the extracted reflection coefficient with different distance between
antennas d (mm). The chart reveals that the value of reflection coefficient at the center
frequency lower than -10 dB. This result indicates that the distance d (mm) does not influence
the center frequency. Figure 3(b) shows that the extracted mutual coupling with varied d (mm).
These results determine that the smaller the antenna distance would be higher the coupling
value.

 ISSN: 1693-6930
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(a) (b)
Figure 3. (a) The extracted reflection coefficient with varied distance d (mm); (b) The extracted
mutual copuling with varied distance d (mm).
Figure 4(a) shows the extracted reflection coefficient with a variable distance between
antennas and radiator H (mm). These results show that the various distance (H) will shift a
center frequency. Moreover, the reflection coefficient at the center frequency is still lower than -
10 dB. Otherwise, Figure 4(b) illustrated the mutual extraction coupling with different distance
between antennas and radiator H (mm). The H is varied from 10 mm to 30 mm. It shows that
the variation of H affected to mutual coupling values but still good isolation.
(a) (b)
Figure 4. (a) The extracted reflection coefficient with varied distance H (mm); (b) The extracted
mutual coupling with varied distance H (mm)
.
3. Results and Analysis
We organize the circular patch MIMO antenna by using a ring and circular parasitic
radiator by special structure as depicted by Figure 1. The size of MIMO antenna are LS = 130
mm, WS = 50 mm, LF = 7.1 mm, WF = 3 mm, LM = 7.9 mm, WM = 1 mm, R = 18.5 mm, h = 1.6
mm, d = 80 mm, R1 = 18 mm, R2 = 11 mm, H = 20 mm, RP = 18.5 mm. This MIMO antenna was
designed on FR4 microstrip substrate with r= 4.4, thickness h=1.6 mm, and tan = 0.0265. An
Advance Design System (ADS) software was used to determine the antenna parameters.
Vector Network Analyzer Agilent N9913A-210 was use to test an antenna performances.
Furthermore, the photograph of fabricated antena was shown in Figure 5.
Figure 6(a) and Figure 6(b) shows a comparison between simulated and measured of
reflection coefficient and mutual coupling of circular patch MIMO antenna by using a ring and
circular parasitic radiator structure. The C-MA antenna [Model-1] achieves center frequency =
2.36 GHz, bandwidth = 70 MHz, reflection coefficient = -12.35 dB, mutual coupling = -30.92 dB.
The RP-MA antenna [Model-2] achieves simulated/measured of center frequency = 2.38
GHz/2.36 GHz, bandwidth = 100 MHz/100 MHz, reflection coefficient = -22.21 dB/ -15.93 dB,
mutual coupling = -28.46 dB/-28.83 dB. The CP-MA antenna [Model-3] achieves

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simulated/measured of center frequency = 2.38 GHz/2.36 GHz, bandwidth = 120 MHz/110 MHz,
reflection coefficient = -23.66 dB/ -24.89 dB, mutual coupling = -27.59 dB/-31.67 dB. A good
agreement can be observed between the simulated and measured results, which demonstrates
the validity of the design.
(a) (b) (c)
Figure 5. (a) Photograph of coventional MIMO antenna (C-MA) [Model 1], (b) Photograph of
MIMO antenna with ring parasitic substrate (RP-MA) [Model 2], (c) Photograph of MIMO
antenna with circular parasitic subtstrate (CP-MA) [Model 3]
(a) (b)
Figure 6. (a) The comparison between simulated and measured of reflection coefficient; (b) The
comparison between simulated and measured of mutual coupling
Figure 7(a) shows the extracted gain and reflection coefficient with varied distance H
(mm). In this reseach, the distance H = 20 mm was used which produce high gain with good
reflection coefficient, simultaneously. Figure 7(b) shows that MIMO antenna with additional a
ring and a circular parasitic radiator structure has higher gain compare to conventional MIMO
antenna. Figure 7(c) and Figure 7(d) show a directivity and effiency, respectively. The charts
show that a directivity and effiency of MIMO antenna with a ring and a circular parasitic radiator
structure has higher value compare to conventional MIMO antenna.
Figure 8(a) displays the surface current distribution of circular antenna. The surface
current distribution flowed only at the circular pacth. Furthermore, Figure 8(b) shows the surface
current distribution of circular antenna with parasitic ring substrate. The surface current
distribution flowed not only at the circular patch but also at parasitic ring substrate. Moreover,
Figure 8(c) shows the surface current distribution of circular antenna with circular parasitic
substrate. The surface current distribution was flowed not only at the circular patch but also at
circular parasitic substrate.
H
Hd d
R R1
R2
RP
LS LS
WS
WS
d
WS
LS

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(a) (b)
(c) (d)
Figure 7. (a) The extracted gain and reflection coefficient with varied distance H (mm), (b) The
comparison of gain (dBi), (c) The comparison of directivity (dBi), (d) The comparison of
efficiency (%)
(a) (b) (c)
Figure 8. (a) The surface current distribution of circular antenna, (b) The surface current
distribution of circular antenna with ring parasitic substrate, (c) The surface current distribution
of circular antenna with circular parasitic subtstrate
Figure 9(a), Figure 9(b), and Figure 9(c) espose radiation pattern of coventional MIMO
antenna (C-MA) [Model 1], MIMO antenna with ring parasitic substrate (RP-MA) [Model 2] and
MIMO antenna with circular parasitic subtstrate (CP-MA) [Model 3].

1161
(a) (b)
(c)
Figure 9. (a) Radiation pattern of coventional MIMO antenna (C-MA) [Model 1], (b) Photograph
of MIMO antenna with ring parasitic substrate (RP-MA) [Model 2], (c) Radiation Radiation
pattern pattern of MIMO antenna with circular parasitic subtstrate (CP-MA) [Model 3]
Table 1 summarizes the comparison of coventional MIMO antenna (C-MA) [Model 1],
MIMO antenna with ring parasitic substrate (RP-MA) [Model 2], and MIMO antenna with circular
parasitic subtstrate (CP-MA) [Model 3].
Table 1. Comparison of C-MA Antenna, RP-MA Antenna and CP-MA performances
Variables
C-MA
[Model 1]
RP-MA
[Model 2]
CP-MA
[Model 3]
Simulated Simulated Measured Simulated Measured
Center Frequency (GHz) 2.36 2.38 2.36 2.38 2.36
Bandwidth (MHZ) 70 100 100 120 110
Gain (dBi) 1.625 4.066 NA 4.117 NA
Directivity (dBi) 6.414 7.265 NA 7.153 NA
Efficiency (%) 33.9 47.8 NA 49.70 NA
Reflection coefficient (dB) -12.35 -22.21 -15.93 -23.66 -24.89
Mutual coupling (dB) -30.924 -28.46 -28.83 -27.59 -31.67
Size
W (mm) 50 50 50 50 50
L (mm) 130 130 130 130 130
H (mm) 1.6 23.2 23.2 23.2 23.2
4. Conclusion
A novel configuration of circular patch MIMO antenna using a ring and circular parasitic
radiator structure have been simulated, fabricated, and measured. The C-MA antenna [Model-1]
achieves center frequency = 2.36 GHz, bandwidth = 70 MHz, reflection coefficient = -12.35 dB,
mutual coupling = -30.92 dB. The RP-MA antenna [Model-2] achieves simulated/measured of
center frequency = 2.38 GHz/2.36 GHz, bandwidth = 100 MHz/100 MHz, reflection coefficient =

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-22.21 dB/ -15.93 dB, mutual coupling = -28.46 dB/-28.83 dB. The CP-MA antenna [Model-3]
achieves simulated/measured of center frequency = 2.38 GHz/2.36 GHz, bandwidth = 120
MHz/110 MHz, reflection coefficient = -23.66 dB/ -24.89 dB, mutual coupling = -27.59 dB/-31.67
dB. A good agreement can be observed between the simulated and measured results, which
demonstrates the validity of the design. This result also validates that the addition circular patch
MIMO antenna with a ring and circular parasitic radiator structure could increase bandwidth and
gain of MIMO antenna simultaneously. Thus, the proposed MIMO antenna is suitable for LTE
application in Indonesia.
Acknowledgments
The work for this grant was supported by the Ministry of Research, Technology and
Higher Education, Indonesian Government in Penelitian Kerjasama Perguruan Tinggi (Grand
No. 267/UN43.9/PL/K/2016).
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Bandwidth and Gain Enhancement of MIMO Antenna by Using Ring and Circular Parasitic with Air-Gap Microstrip Structure

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