A Design of Decoupling Structure MIMO Antenna

for Mutual Coupling Reduction in 5G Application

H. Yon¹, M.A Aris¹, N. H. Abd Rahman¹ ², N.A. M Nasir¹, H. Jumaat¹ ¹Antenna Research Centre (ARC), Faculty of Electrical Engineering, Universiti Teknologi MARA, Shah Alam, Selangor 40450,

Malaysia.

²Malaysia Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, 54100, Kuala

Lumpur, Malaysia

hamizanyon@gmail.com , mohdazizbinaris@gmail.com, nurulhuda0340@gmail.com, nuratiqah@asia.com,

jumaathadi@gmail.com,

Abstract— A new antenna structure with low mutual coupling between 2 antenna elements for MIMO has been developed and presented in this paper. The decoupling

structure has been analyzed and designed between both antennas to suppress the isolation between dual elements. Nine different structures has been designed and 28.75%

improvement on isolation has been achieved from pattern 3 decoupling structure. By using the decoupling structure, the antenna bandwidth has been improved tremendously to

20.8%. The antenna has been printed with full copper ground on the bottom layer. The antenna was simulated and optimized at 16 GHz using Computer Simulation Technology (CST) with

permittivity, r = 2.2 and thickness, h = 1.57mm on Rodges RT-Duroid 5885 substrate. The antennas are matched at their corresponding frequency of operations. The simulation and

fabrication results have shown that the antenna works well.

Index Terms—MIMO, Decoupling Structure, CST, Rodges.

I. INTRODUCTION

Researchers have focused on the MIMO antenna because

of its advantages especially on high capacity and high speed

wireless communication[1]. Moreover, in the new era, there

has been an increase in demand with MIMO antenna to

support the growing number of devices that demands

internet usages for 5G technology [2]. Therefore, there is a

need to designing a compact antenna with multiple input

and output. MIMO it’s the best configuration antenna that

matches all the requirement for 5G technology. The crucial

design challenge for MIMO antenna is to reduce mutual

coupling.

The traditional way to reduce mutual coupling is by

separating antenna distance, however this method will

increase the total size of the antenna. Decoupling structure is

a method that can be used to reduce mutual coupling

between antennas[3]. Further investigation on the concept of

decoupling technique and it structure in order to improve

mutual coupling and improve antenna performance are

discussed in this paper.

II. ANTENNA DESIGN

1 2 3 4 5 6 7 8 9

Figure 1. 9 decoupling structure pattern

As shown from the Fig. 1, nine decoupling structures

(pattern 1 to pattern 9) has been studied to improve antenna

isolation. The width size (W) of the decoupling structure

has been studied with 0.5mm, 1.0mm and 1.5mm,

respectively. Each of the decoupling structure has its

advantages as shows in Fig. 2 in term of isolation and

bandwidth. Deeper analysis has been studied in[4]–[9] to

design different shaped of decoupling structure in order to

develop new structure and improvement MIMO

performance in this research work.

Size, mm

0.6 0.8 1.0 1.2 1.4

Isol

atio

n, d

B

-45

-40

-35

-30

-25

-20

-15

Decoupling Pattern 1

Decoupling Pattern 2

Decoupling Pattern 3

Decoupling Pattern 4

Decoupling Pattern 5

Decoupling Pattern 6

Decoupling Pattern 7

Decoupling Pattern 8

Decoupling Pattern 9

Bandwidth, GHz

1.4 1.5 1.6 1.7

Siz

e, m

m

0.6

0.8

1.0

1.2

1.4

Decoupling Pattern 1

Decoupling Pattern 2

Decoupling Pattern 3

Decoupling Pattern 4

Decoupling Pattern 5

Decoupling Pattern 6

Decoupling Pattern 7

Decoupling Pattern 8

Decoupling Pattern 9

Figure 2. Simulation for Isolation and bandwidth comparison

Fig. 2 shows the relationship between decoupling size

and pattern towards isolation performance. From the figure,

decoupling structure with Pattern 3, size 0.5mm shows

value in terms of isolation compared with other structure.

The improvement 28.75% of isolation has been achieved

from this pattern compared with antenna without decoupling

structure in simulation process.

III. RESULT

Figure 3. Simulation reflection coefficient comparison

Figure 4. Simulation isolation comparison

Figure 5. Simulation radiation pattern comparison

The simulation result for the antenna with decoupling

structure Pattern 3 is shown in Fig. 3, Fig. 4 and Fig. 5.

From the result, it has shown that the decoupling structure

with 0.5mm size has improved isolation better compared to

the 1.0mm and 1.5mm. As a result, the final antenna will

fabricated and measured with a 0.5mm decoupling size.

Fig. 6 shows the antenna reflection coefficient that has

been measured using Vector Network Analyzer. The antenna

has been measured in order to determine the feasibility of the

fabricated design. The antenna without decoupling was -

18.44dB at 16.02GHz for port 1 and -18.34 on port 2 at

15.94GHz. Meanwhile, for antennas with decoupling

structure are reduce to -12.94dB at port 1 and -12.05 at port

2. The reflection coefficient are reduced, this is due to

improper on fabricated process and handling antenna

structure during measurement process.

Figure 6. Measurement result (a) without (b) with decoupling

Meanwhile, Fig. 7 shows good results at the isolation

between antenna where the antenna isolation is achieved at -

31.28dB with decoupling structure and -26.76dB without

decoupling structure.

Figure 7. Measurement result (a) without (b) with decoupling

The radiation pattern was measured in an indoor anechoic

chamber using the Far-field measurement at selected

operating frequency. The fabricated antenna exhibits a

dominant wave distribution at E-Plane with a simulated

radiation pattern that radiates at 0º angle. The radiation

pattern measurement has been held in E-Plane condition and

also in H-Field to ensure antenna radiation pattern same as a

simulated result.

Figure 8. Antenna measurement process and fabricated antenna design

Figure 9. Comparison port 1 and port 2 with decoupling structure

The measurement pattern shows that close similarities to

the simulated result. The measured radiation pattern at the

selected frequency is close to the directional radiation

pattern. The measurement result of the fabricated antenna

without decoupling structure was 6.21dBi in gain at a

16.08GHz operating frequency and with an antenna

efficiency of 63.58% for port 1 and 6.28dBi in gain at

15.94GHz and 67.32% of efficiency for port 2. Meanwhile,

the antenna gain for an antenna with decoupling structure

slightly increases to 6.41dBi on 16.06GHz with efficiency

of 62.17% and 6.30dBi in gain for port 2 with operating

frequency at 15.96GHz and efficiency of 65.29%. The gain

and the antenna efficiency are expected to drop from the

simulation results due to losses that occurred from the

fabricated antenna process and the alignment itself.

Summary of the measurement result is shows in table 1.

TABLE I ANTENNA COMPARISON WITH AND WITHOUT DECOUPLING

Description Fo

(GHz)

Gain

(dBi)

Isolation

(dB)

Eff

(%)

Simulation Port 1 16.02 7.47 -26.57 82.09

With

out

Deco

up

ling

Stru

cture

Port 2 16.02 7.47 -26.57 82.09

Measurement Port 1 16.08 6.21 -26.76 63.58

Port 2 15.94 6.28 -26.76 67.32

Simulation Port 1 16.06 7.58 -34.08 81.07

With

Deco

up

ling

Stru

cture

Port 2 16.06 7.58 -34.08 81.07

Measurement Port 1 16.06 6.41 -31.28 62.17

Port 2 15.96 6.30 -31.28 65.29

IV. CONCLUSIONS

In this paper, a novel decoupling structure for 5G

antenna applications has been presented. The antenna design

has good performance using decoupling structure with

0.5mm to improve MIMO isolation for 17.90% on

measurement result. The -10dB impedance bandwidth is

increased as much as 25.7% without decoupling and

decreased 7% for antenna with decoupling structure. The

reducing in measurement result for isolation, bandwidth and

gain is believed due to handling and fabrication error on

measurement process.

ACKNOWLEDGMENT

The author would like to thank Universiti Teknologi

MARA for sponsoring the work. Express gratitude to the

members of the Antenna Research Centre (ARC), Faculty of

Electrical Engineering, Universiti Teknologi MARA for

supporting the research works.

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Decoupling

Structure