Thiết kế anten MIMO ba băng với độ tương hỗ thấp sử dụng cấu trúc mặt đất khuyết DGS

TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
Số 12 tháng 5-2017 
19 
TRIPLE-BAND MIMO ANTENNA DESIGN WITH LOW MUTUAL 
COUPLING USING DEFECTED GROUND STRUCTURE 
THIẾT KẾ ANTEN MIMO BA BĂNG VỚI ĐỘ TƢƠNG HỖ THẤP 
SỬ DỤNG CẤU TRÚC MẶT ĐẤT KHUYẾT DGS 
Duong Thi Thanh Tu
1,2
 , Nguyen Gia Thang
1
, Vu Van Yem
2
1
Faculty of Telecommunication1, Posts and Telecommunications Institute of Technology 
2
School of Electronics and Telecommunications, Hanoi University of Science and Technology 
Abstract: 
The multiband MIMO antenna design for broadband mobile’s applications is proposed in this paper. 
The proposed MIMO antenna that is based on the PIFA structure and designed on FR4, gets compact 
in size with total dimension of 37x43.6x6 mm3. At first, a MIMO PIFA antenna is presented using U-
shaped Slots on radiating patch and two rectangular DGSs on the ground plane which puts forward 
the antenna resonant in three frequencies: 2.46 GHz, 3.3 GHz, and 6.3 GHz with bandwidths of 
8.44%, 9.76% and 2.3% respectively for Wi-Fi, Wimax/LTE and Direct Broadcast Satellite DBS of C 
channel applications. Good return loss, antenna gain, and radiation pattern characteristics are 
obtained in the frequency band of interest. Then, to reduce the mutual coupling between antenna 
elements at close distance of 4 mm, equivalent to 0.032 at 2.4 GHz resonant frequency, a novel 
“slot and variation structure” of DGS is proposed. Moreover, this DGS has enhanced MIMO antenna 
bandwidth at all three bands, especially at 3.5GHz resonant frequency. 
Key words: 
PIFA, MIMO, DGS, low mutual coupling MIMO antenna. 
Tóm tắt: 
Nội dung bài báo đề xuất một kiến trúc anten MIMO đa băng cho các ứng dụng băng rộng trong các 
thiết bị cầm tay di động. Với cấu trúc PIFA, anten MIMO đề xuất sử dụng vật liệu FR4 đạt được kích 
thước khá nhỏ 37x43.6x6 mm3. Cộng hưởng tại 3 tần sô 2.46 GHz, 3.3Ghz và 6.3 GHz nhờ khe chẻ 
hình chữ U trên mặt bức xạ với độ rộng băng thông tương ứng 8.44%, 9.76% và 2.3%, anten có 
thể đáp ứng được đồng thời cho các ứng dụng WiFi, Wimax/LTE và vệ tinh băng C. Các tham số 
anten khác như độ lợi, suy hao phản xạ, hiệu suất bức xạ, đều đạt chuẩn công nghệ. Không 
những thế, nhờ sử dụng cấu trúc mặt phẳng đất khuyết (DGS), anten MIMO đề xuất đạt độ cách ly 
cao (S12<-20 dB) với khoảng cách giữa hai phần tử bức xạ khá nhỏ, 4mm, tương đương với 0.032 
tại tần số cộng hưởng 2.4GHz. Bên cạnh đó, nhờ cấu trúc DGS này, băng thông của anten MIMO 
cũng được mở rộng thêm, đặc biệt tại tần số cộng hưởng 3.5G Hz. 
Từ khóa: 
PIFA, MIMO, DGS, anten MIMO có độ tương hỗ thấp.3 
3
 Ngày nhận bài: 16/9/2016, ngày chấp nhận đăng: 15/3/2016, phản biện: TS. Nguyễn Lê Cường. 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
 Số 12 tháng 5-2017 
20 
1. INTRODUCTION 
Recently, the wireless communication 
system has advanced incredibly, 
especially in mobile phone system. It is 
not only the dimensions of end use 
equipment more and more decrease but 
also the number of internal antennas in 
one terminal increase rapidly [1-2]. These 
demand the internal antennas must 
compact to build in practical mobile 
handsets and have multiband for multi 
technologies. In last three decades, Planar 
Inverted F Antenna (PIFA) has emerged 
as one of the most promising candidate 
for satisfying above demands [2-3]. 
However, one of the limitations of PIFA 
antenna is narrow bandwidth which 
makes this antenna type unsuitable for 
wide-band commercial applications. 
To make multiband PIFA antenna, there 
are several methods that have been 
proposed such as meandering the main 
radiating element [4], using fractal 
method [5] or introducing slot on the 
ground plane [6]. These techniques 
achieve multiband operation but get the 
performance degradation. Another 
technique is using multi-stacing or multi-
shorting pins [7]. However, this method is 
not only complex to fabricate but also 
needs much effort in assembling the PIFA 
antenna to get multiband operation. 
Besides, Multiple Input Multiple Output 
(MIMO) technology has attracted much 
attention presently in the terminal of 
modern wireless communication systems 
such as: 802.11n, 802.11ac, 802.16m, 
LTE-advanced, 5G. The most significant 
feature of MIMO is the high channel 
capacity increasing without bandwidth 
addition or transmission power 
increasing. However, MIMO antenna 
systems require high isolation between 
antenna elements and a compact size for 
application in portable devices. There are 
many methods have been proposed 
for improving the isolation between 
antenna elements in the MIMO system 
such as using transmission line 
decoupling technique [8], neutralization 
line technique [9], covering the patch by 
additional dielectric layers [10], using 
shorting pins for cancellation of 
capacitive polarization currents of the 
substrate [11] or using photonic band gap 
structures such as defected ground 
structure (DGS) and EBG [12-14]. 
However, most of these studies have 
focused on the applications for single 
band antenna design and a few for dual 
band MIMO antenna system. The design 
of MIMO antenna with high isolation for 
triple band or more with narrow distance 
is still a huge challenge in MIMO system 
for handheld applications. 
In this paper, a triple band MIMO antenna 
with high isolation is proposed. Two U 
shaped slots into the main radiating patch 
of PIFA antenna is inserted to achieved 
tri-band operation at 2.46 GHz, 3.3 GHz 
and 6.3 GHz for Wi-Fi, Wimax/ LTE-
advanced and Direct Broadcast Satellite 
DBS of C channel applications. The total 
dimension of MIMO antenna is 37 × 43.6 
× 6 mm
3
 that is compact for handheld 
portable devices. 
2. PROPOSED ANTENNA STRUCTURE 
The geometric structure of the proposed 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
Số 12 tháng 5-2017 
21 
tri-band PIFA MIMO antenna is shown in 
figure 1. The antenna consists of three 
main elements which are finite ground 
plane, top radiating patch and shorting pin 
that connects between the top radiating 
patch and ground plane. 
(a) Top plane 
(b) Bottom plane 
(c) 3D 
Figure 1. Proposed triple-band MIMO antenna 
At first, the total dimension of main 
radiating patch need to be calculated 
according to the desired resonant 
frequency. There are three different 
operating frequencies for the tri-band 
operation. Therefore, the lowest 2.4 GHz 
resonant frequency is chosen to calculate 
the total length (lp) and width (wp) of the 
patch by equation (1). 
 ( )
 (1) 
where c is the speed of light, lp and wp are 
the length and the width of top radiating 
plate and f0 is resonant frequency. 
Then, two slots with U-Shaped structure 
have been chosen to make the second and 
the third resonant frequencies. The 
resonant frequencies are approximated by 
formula (2): 
 ( )√ 
(2) 
 ( )√ 
where r is the relative permittivity of the 
medium between the ground and radiating 
patch, h is the height of the patch in 
reference to the ground. To improve the 
performance of PIFA antenna, the double 
rectangular DGS structures are inserted in 
the ground of each antenna elements [15]. 
After that, a MIMO model is constructed 
by placing two antenna elements side by 
side at the distance of 23.8 mm from 
feeding point to feeding point, equals to 
0.5 at 6.3 GHz resonant frequency or 
0.19 at 2.4 GHz. From edge to edge, the 
distance between two patches of MIMO 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
 Số 12 tháng 5-2017 
22 
antenna is 4 mm, equivalent to 0.032 at 
2.4 GHz resonant frequency. The total 
dimension of MIMO antenna is 37 × 43.6 
× 6mm
3
 that is compact for handheld 
applications. 
(a) (b) 
Figure 2. The slot load DGS structures 
(a)Double square shape, (b)Periodic 
rectangular shape 
Table 1. Detail dimension of proposed MIMO 
antenna 
Parameter 
Value 
(mm) Parameter 
Value 
(mm) 
lg 37 w2 8 
wg 43.6 lp 19.6 
l1 9.2 wp 19.8 
w1 18 de 4 
l2 6 df 23.8 
Finally, to reduce the mutual coupling 
MIMO elements for all three bands of 
antenna, two coordinated “slot and 
variation” shape of DGS structures are 
used on the ground plane. As shown in 
Figure 2, the small DGS structure with 
8-shape is coordinated the long one with 
periodic loop shape to increase the 
isolation at 2.44 GHz, 3.3 GHz and 
6.3 GHz resonant frequencies concurrently. 
The dimensions of these DGS structures 
are optimized by CST software. The 
detail dimension of the proposed MIMO 
antenna is shown on table 1. 
3. SIMULATION RESULTS 
The performance of proposed MIMO 
antenna has simulated in CST software. 
The S parameters of MIMO system is 
shown in figure 3 with the distance of two 
antenna elements from feed to feed is 
changed from 62.5 mm (0.5 at 2.4 GHz 
resonant frequency) down to 23.8 mm 
(0.5 at 6.3 GHz resonant frequency). 
Figure 3. The S parameters of MIMO system 
with distance is changed from 62.5 mm 
down to 23.8 mm 
It is clearly seen that there are three 
frequencies at which resonance occurs. 
They are 2.46 GHz, 3.3 GHz and 
6.32 GHz. Thanks to double rectangular 
DGS structures, the mutual coupling 
between antenna elements is quite low 
with the distance of 0.5 at 2.4 GHz 
resonant frequency. At this distance, the 
S12 gets -28 dB at 2.4 GHz as well as 
6.3GHz and -30 dB at 3.5 GHz. These 
values of S12 increase gradually and 
reach -20 dB at distance of 39.28 mm 
which equal in 0.31 at 2.4 GHz or 0.46 
at 3.5 GHz. At distance of 23.8 mm (0.5 
at 6.3 GHz), the bandwidths of MIMO 
antenna get 202.6 MHz, 341.7 MHz and 
145.9 MHz and the S12 values reach 
-16 dB, -13 dB and -19 dB at 2.4 GHz, 
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Số 12 tháng 5-2017 
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3.5 GHz and 6.3 GHz respectively. 
To reduce the mutual coupling between 
two antenna elements at this close 
distance, two “slot and variation” DGS 
structures with 8-shape and periodic loop 
shape are proposed. 
Figure 4. The S parameters of MIMO system 
using DGS with the distance of 4mm 
from edge to edge 
The figure 4 shows the S parameters of 
the MIMO antenna using the “slot and 
variation” DGS structures for the distance 
of 23.8 mm (0.5 at 6.3 GHz) from feed 
to feed. This distance equals the distance 
of 4 mm from edge to edge. It is a so 
narrow distance between two antenna 
elements in a MIMO system. It is clearly 
seen that the MIMO antenna using the 
DGS gets the high isolation between 
antenna elements (S12 <-20 dB) at all 
three bands. Moreover, by applying DGS 
structure on the ground, several 
performance parameters of MIMO 
antenna are improved. First of all is the 
bandwidth. The bandwidth of MIMO 
antenna at all three bands are increased 
and get 209.5 MHz, 573.5 MHz and 
150.7 MHz at 2.44 GHz, 3.33 GHz and 
6.32 GHz respectively. There is a 
significant increase of 231.85 MHz at 
3.5 GHz resonant frequency. 
Table 2. The radiation efficiency and gain 
Frequency 
(GHz) 
Radiation 
Efficiency (%) 
Gain(dB) 
With 
DGS 
Without 
DGS 
With 
DGS 
Without 
DGS 
2.4 99.94 98.51 3.6 3.56 
3.5 99.6 98.35 4.55 4.24 
6.3 93.55 81 5.86 5.85 
Then, the radiation efficiency and gain of 
MIMO antenna are also improved lightly 
as shown in table 2. In addition, from 
figure 5, it is clearly seen that, the 2D 
radiation pattern of MIMO antenna is 
smooth for all of three bands and angular 
width (3 dB) is 117; 127 and 96 degree 
at 2.4 GHz, 3.5 GHz and 6.3 GHz 
respectively. 
Figure 5. The 2D radiation pattern of MIMO 
antenna using “slot and variation” DGS 
Moreover, the proposed MIMO antenna is 
compared to another MIMO design 
without connecting ground between 
antenna elements as shown in figure 6. 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
 Số 12 tháng 5-2017 
24 
Figure 6. MIMO antenna 
without connecting ground 
The comparison of S parameters between 
the proposed MIMO antenna and the 
MIMO antenna without connecting 
ground is illustrated in figure 7. 
Figure 7. Comparison of S parameters between 
the proposed MIMO antenna and the MIMO 
antenna without connecting ground 
It is clearly seen that the MIMO antenna 
without connecting ground gets high 
mutual coupling between antenna 
elements. At 2.28 GHz resonant 
frequency, antenna mutual coupling gets -
7 dB and at 3.7 GHz resonant frequency, 
it is -10 dB. Thus, several antenna 
parameters tend to drop such as 
bandwidth, desired resonant frequency. 
4. MEASUREMENT RESULTS 
The proposed triple-band MIMO antenna 
is fabricated on the FR4 substrate as 
shown in figure 8. 
(a) Top view (b) Bottom view 
Figure 8. Fabricated triple-band MIMO antenna 
Figure 9. Comparison of S parameters between 
measurement results and simulation results 
The antenna gets compact in size of 
37×43.6×6 mm
3
. The measured results of 
S parameters are compared to simulation 
ones in figure 9. It is clearly seen that 
the MIMO antennas operate at about 
2.4 GHz, 3.5 GHz and 5.7 GHz with over 
10%, 20% and 4% bandwidth, respectively. 
The mutual coupling at all interest bands 
are under-20dB. It can be concluded that 
the measured results agree well with the 
simulated ones. Thus, using the proposed 
“slot and variation” DGS structures can 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
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Số 12 tháng 5-2017 
25 
reduce the mutual coupling between 
antenna elements in triple-band MIMO 
antenna. 
5. CONCLUSION 
In this paper, a compact triple band 
MIMO PIFA antenna using U-shape slots 
as well as the coordinate double 
rectangular with the “slot and variation” 
DGS structures is proposed. The total 
MIMO antenna occupies a small area of 
37 × 43.6 mm
2
 on the FR4 substrate and 
can operate at 2.4 GHz, 3.5 GHz and 
6.3 GHz. The MIMO antenna gets the 
large bandwidths which are 209.5 MHz, 
573.5 MHz and 150.7 MHz at 2.4 GHz, 
3.5 GHz and 6.3 GHz respectively. These 
results have solved the narrow bandwidth 
limitation of conventional PIFA. In 
addition, using novel DGS structures, the 
antenna not only gets the extremely high 
radiating efficiency of 99.94%; 99.6% 
and 93.55% but also gets the high gain of 
the antenna which is respectively 3.6 dB, 
4.55 dB and 5.86 dB at 2.4 GHz, 3.5 GHz 
and 6.3 GHz operating frequency. 
Besides, the MIMO antenna has ensured 
the mutual coupling between antenna 
elements under -20 dB for all three bands 
with the narrow distance of 4mm from 
edge to edge of two antenna elements. 
This proposed antenna is suitable for 
handheld terminals of Wi-Fi, Wimax/LTE 
and C-band satellite applications. 
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Biography: 
Duong Thi Thanh Tu, received B.E, M.E degrees in Electronics and 
Telecommunications from Hanoi University of Science and Technology and 
National University in 1999 and 2005, respectively. She now is a lecturer at 
Faculty of Telecommunications 1, Posts and Telecommunications Institute of 
Technology. She, presently is doing PhD at School of Electronics and 
Telecommunications, Hanoi University of Science and Technology. Her current 
research centers on antenna design for next generation wireless networks as 
well as the special structure of material such as metamaterial, electromagnetic 
band gap structure.