High gain 5G MIMO antenna for mobile base station

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 9, No. 1, February 2019, pp. 468~476
ISSN: 2088-8708, DOI: 10.1159 1/ijece.v9i1 .pp468-476 o 468

High gain 5G MIMO antenna for mobile base station

Yusnita Rahayu!, Indah Permata Sari’, Dara Incam Ramadhan’, Razali Ngah‘
'23Faculty of Engineering, Department of Electrical Engineering, Universitas Riau, Indonesia
4Wireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, Malaysia

Article Info

ABSTRACT

Article history:

Received Dec 20, 2017
Revised Aug 16, 2018
Accepted Aug 31, 2018

This article presented a millimeter wave antenna which operated at 38 GHz
for 5G mobile base station. The MIMO (Multiple Input Multiple Output)
antenna consisted of 1x10 linear array configurations. The proposed
antenna’s size was 88 x 98 mm? and printed on 1.575 mm-thick Rogers
Duroid 5880 subsrate with dielectric constant of ¢-=2.2 and loss tangent

(tand) of 0.0009. The antenna array covered along the azimuth plane to

provide the coverage to the users in omnidirection. The simulated results
Keywords: showed that the single element antenna had the reflection coefficient (S11) of
5G -59 dB, less than -10 dB in the frequency range of 35.5-39.6 GHz. More than
4.1 GHz of impedance bandwidth was obtained. The gain of the antenna
Antenna array linear array was 17.8 dBi while the suppression of the side lobes was -2.7 dB.
Base station It showed a high array gain throughout the impedance bandwidth with
High gain overall of VSWR were below 1.0646. It designed using CST
MIMO sntenna microwave studio.

Copyright © 2019 Institute of Advanced Engineering and Science.
All rights reserved.

Corresponding Author:

Yusnita Rahayu,

Department of Electrical Engineering,
Universitas Riau, Pekanbaru, Indonesia.
Email: yusnita.rahayu@lecturer.unri.ac.id

1. INTRODUCTION

The fifth generation (5G) mobile technology has been introduced and expected to be deployed in
year 2020 [1]. In order to meet the fast growing wireless data capacity demands due to increasing users of
smartphones, high growth in web and streaming, 5G technology now are highly given attention and undergo
a huge research [2]. The 5G technology comes to solve problems and needs to improve network efficiency
and capacity, improved data rates with better coverage at lower power consumption. Future 5G wireless
systems have to satisfy three main requirements: i) having a high throughput; ii) simultaneously serving
many users; and iii) having less energy consumption [3]. In the 5G era, lots of things such as electronic
devices, vehicles and the equipment in the offices and homes will be wirelessly connected through the
Internet. Users will be able to access ultra-high-definition (UHD) multimedia streaming and services such as
Virtual Reality (VR) and Augmented Reality (AR) [4]. Untill now 5G standards are not available for us.
However, some researches have started to put the base or the technology that will provide these standards.
This technology mostly consists of wireless access systems, frequency utilization, power consumption,
antenna and propagation [5].

The demand for higher quality and data rate was growing fast in the past few years. One of the most
promising solutions to this problem is Multiple Input Multiple Output (MIMO) system. The MIMO
technology made a great breakthrough by satisfying the demand of higher quality mobile communication
services without using any additional radio resources and it has a significant ability to increase data
throughput without additional bandwidth or transmit power (transmitter power). One type of antenna that can
be used to increase the channel capacity of MIMO is a microstrip antenna [6]. The microstrip antenna has
many benefits such as low cost, low profile, ease fabrication, and compact [7].

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Int J Elec & Comp Eng ISSN: 2088-8708 o 469

Massive MIMO technology and millimeter wave (mm Wave) communication has been considered
as a key technology for the fifth generation wireless communication [8]. Mm-wave generally corresponds to
30-300 GHz frequency bands, but sometimes 10-30 GHz frequency bands are also included as they share
some similar propagation characteristic [9]. Some of the candidate bands or 5G communications in the
frequency of 20-50 GHz are specified in Figure 1. [10].

21.2 23.6 27.5 29.5 3131.3 36 40 41 42.5 45.5 47 47.2 50.2

GHz

Figure 1. The candidate bands for the future 5G system in 20-50 GHz [10]

For mm-wave applications, problems to be concerned are the higher transmission loss and link
stability, which could be overcome by increasing the gain and adopting the adaptive directional beam [4].
Massive MIMO base station is a promising technique for improving the capacity and service quality by
accurately concentrating the transmitted energy to the mobile users [11]-[12]. Massive MIMO or large
antenna array system has the capability of greatly improving spectral efficiency, energy efficiency, and
system robustness [13]-[14]. In a typical massive MIMO system, single antenna mobile stations (MSs)
communicate with a base station (BS) equipped with a large number of antennas [15].

The combination of mmWave and massive MIMO has the potential to dramatically improve
wireless access and throughput performance such system benefit from large available signal bandwidth and
small antenna form factor. the system also have advantages in terms of compact dimensions, energy
efficiency, flexibility, and adaptivity that would make them ideally suited for 5G communication
system [16]-[19]. In this paper, we proposed a high gain linear array 1x10 MIMO antenna which is used in
5G mobile base station operating at 38 GHz. The antenna has broad bandwidth with nearly omni directional
pattern. The gain reached more than 17 dBi. This gain is relative high for omnidirectional pattern and
broadband antenna.

2. RESEARCH METHOD

In this section, four (4) linear array configurations antennas, single element; 1x6 elements;1x8
elements; and 1x10 elements will be described. First, single element antenna is designed to meet the desired
requirement such as frequency (38 GHz) and return loss. Then, this single element is used to form the MIMO
configurations, 1x6 elements, 1x8 elements and 1x10 elements.

2.1. Single element antenna

The substrate selection is the first step in the designing of patch antenna. This paper uses RT Duroid
5880 as a substrate of the proposed antenna. The substrate parameters are summarized in Table 1.
The geometry of single element antenna is shown in Figure 2 and the dimensions are summarized in Table 2.

Table 1. RT Duroid 5880 Parameters Table 2. Single Element Antenna Parameters
Parameters Value Parameters Value (mm)
Dielectric constant (e+) 2.2 W 8.8
Substrate thickness (h) 1.575 mm L 9.8
Loss tangent (ô) 0.0009 H 1.575

Wt 2.4

Lf 4

Wp1 1

Lpl 1

Wp2 1

Lp2 2

Wp3 1

Lp3 0.5

Lp4 1.5

High gain 5G MIMO antenna for mobile base station (Yusnita Rahayu)

470 o ISSN: 2088-8708

i \ : a ¥
a Z. m
(a)

Figure 2. The geometry of single element antenna design, (a) 3D view, (b) top layer

(b)

3. RESULTS AND ANALYSIS
3.1. Single element

The significant importance in antenna design is the reflection coefficient (S11) that defines the
bandwidth and the impedance matching characteristic. The simulated result of the return loss for single
element antenna is depicted in Figure 3.

The simulated results show that the single element antenna has the reflection coefficient (S11) of -59
dB, less than -10 dB in the frequency range of 35.5-39.6 GHz. More than 4.1 GHz of impedance bandwidth
is obtained. Another imperative parameter beside the reflection coefficient and input impedance, that reflects
the antenna performance, is the VSWR (Voltage Standing Wave Ratio), the antenna only can be able to
operate at frequencies where the values of VSWR are inferior to 2 [20]. From Figure 4, we can see that the
VSWR value is less than 2.

The 2D and 3D simulated radiation pattern of the antenna design are presented in Figure S.
The radiation pattern of single element antenna provides gain of 7.66 dBi with side lobe level is -2.1 dB.
Total efficiency is -0.978 dB.

S-Parameter [Magnitude in dB]

33 34 35 36 37 38 39 40 41 42 43
Frequency / GHz

Figure 3. Simulated reflection coefficient (S11) characteristics of the single element antenna

Voltage Standing Wave Ratio (VSWR)

|

33 34 35 36 37 38 39 40 41 42 43
Frequency / GHz

Figure 4. VSWR value of the single element antenna

Int J Elec & Comp Eng, Vol. 9, No. 1, February 2019 : 468 - 476

Int J Elec & Comp Eng ISSN: 2088-8708 m) 471

Farfield Directivty Abs (Azimuth=0) E-Vecter

farfield (f=38) [1]
Azimuth=180

Frequency = 38

30 Main lobe magnitude = 7.67 dBi
Main lobe direction = 64.0 deg.

Angular width (3 dB) = 58.6 deg.
Side lobe level = -2.1 dB

Elevation / Degree vs. dBi

(a) (b)

Figure 5. Radiation pattern of the single element antenna, (a) 2D model, (b) 3D model

3.2. MIMO 1x6 elements

The Figure 6 shows the design of MIMO antenna with six element antenna. The simulated radiation
patterns are presented in Figure 7. It was observed when elements were assembled in the form of six element
antenna linear array, there was an increase in antenna gain from 7.66 dBi to 15.6 dBi with side lobe level
is -2.8 dB. Total efficiency antenna is -1.371 dB. Simulated S-parameters of the arrays are illustrated in
Figure 8, the isolations between the consecutive ports, S21, S32, S43 etc., are well below -20dB which show
a lesser mutual coupling between them.

52.8mm

j a a a a

Figure 6. The geometry of six element MIMO antenna design

Farfield Directivity Abs (Azimuth=0) E-Vecter ai

—— farfieki (f=38) [1[1,0]+2[1...
Azimuth=180

& -30 «l
` \ Side lobe level = -2.8 dB
Ho

Elevation / Degree vs. dBi

(a) (b)

Figure 7. Radiation pattern of six element antenna, (a) 2D model, (b) 3D model

High gain 5G MIMO antenna for mobile base station (Yusnita Rahayu)

472 Oo ISSN: 2088-8708

S-Parameter [Magnitude in dB]

33 34 35 36 37 38 39 40 41 42 43
Frequency / GHz

Figure 8. Simulated reflection coefficient (S11) characteristics of 1x6 element antenna

3.3. MIMO 1x6 elements

The Figure 9 shows the design of MIMO antenna with eight element antenna. The 2D and 3D
simulated radiation pattern are presented in Figure 10. There was an increase in antenna gain from 15.6 dBi
to 16.8 dBi with side lobe level is -2.7 dB. Total efficiency antenna is -1.393 dB. Simulated S-parameters of
the arrays are illustrated in Figure 11, the isolations between the consecutive ports, S21, S32, S43 etc., are
well below -20dB which show a lesser mutual coupling between them.

70.4 mm
œ
3
Figure 9. The geometry of eight element MIMO antenna design
Farfield Directivity Abs (Azimuth=0) E-Vecter dBi

-20 — farfield (f=38) [1[1,0]+2[1...
60 Azimuth=180

Frequency = 38
Main lobe magnitude = 16.8 dBi
Main lobe direction = 63.0 deg.

Angular width (3 dB) = 66.6 deg.
Side lobe level= -2.7 dB

90

Elevation / Degree vs. dBi

(a) (b)

Figure 10. Radiation pattern of the eight element antenna, (a) 2D model, (b) 3D model

Int J Elec & Comp Eng, Vol. 9, No. 1, February 2019 : 468 - 476

Int J Elec & Comp Eng ISSN: 2088-8708 o 473

S-Parameter [Magnitude in dB]

— sit
— $2,1
— 33,1
— s41
— 55,1
— 56,1
J — s71
| — S81
d — 51,2
— 52,2
— 532
— s42
— $5,2
— 56,2
— 57,2
— 58,2

Frequency / GHz

Figure 11. Simulated reflection coefficient (S11) characteristics of 1x8 element antenna

3.4. MIMO 1x10 elements

The Figure 12 show the design of MIMO antenna with ten element antenna. The 2D and 3D
simulated radiation pattern are presented in Figure 13. There was an increase in antenna gain from 16.8 dBi
to 17.8 dBi with side lobe level is -2.7 dB. Total efficiency antenna is -1.408 dB. Simulated S-parameters of
the arrays are illustrated in Figure 14, the isolations between the consecutive ports, S21, S32, S43 etc., are
well below -20dB which show a lesser mutual coupling between them. The performances of the antenna
linear array in terms of gain, efficiency, bandwidth, return loss and mutual coefficient are summarized in
Table 3.

88 mm
bed
oa
Figure 12. The geometry of ten element MIMO antenna design
Farfield Directivity Abs (Azimuth=0) dBi

E-Vector

-20 — farfield (f=38) [1[1,0]+2[1...

Frequency = 38

Main lobe magnitude = 17.8 dBi
Main lobe direction = 63.0 deg.
Angular width (3 dB) = 67.0 deg.
Side lobe level= -2.7 dB

90

Elevation / Degree vs. dBi

(a) (b)

Figure 13. Radiation pattern of the ten element antenna, (a) 2D model, (b) 3D model

High gain 5G MIMO antenna for mobile base station (Yusnita Rahayu)

474 Oo ISSN: 2088-8708

S-Parameter [Magnitude in dB]

— S11
— $21
— 33,1
— 54,1
— 55,1
—— 56,1
— 57,1
— 58,1
— 59,1
4 — s10,1
— 512
= —— 522
53,2
— $4,2
— 55,2
— 56,2

Frequency / GHz

Figure 14. Simulated reflection coefficient (S11) characteristics of ten element antenna

Table 3. The Performances of the MIMO Antenna

Variable Gain Effic. BW Return loss MC
1x1 7.66dBi -0.978 4.1GHz -59 -
1x6 15.6dBi -1.371 4.5GHz -30 -20dB
1x8 16.8dBi -1.393 4.5GHz -30 -20dB
1x10 17.8dBi -1.409 4.5GHz -30 -20dB

4. CONCLUSION

A MIMO antenna which formed by using ten element antenna is designed for 5G mobile base
station that can operate at 38 GHz. The antenna was designed on a Rogers Duroid 5880 as subsrate with
1.575 mm-thickness, dielectric constant of ¢ r=2,2 and loss tangent (tan) of 0,0009. The simulated results
show that the single element antenna has the reflection coefficient (S11) of -59 dB, less than -10 dB in the
frequency range of 35.5 - 39.6 GHz. More than 4.1 GHz of impedance bandwidth is obtained.

The MIMO antenna covers along the azimuth plane to provide the coverage to the users in
omnidirection. When elements were assembled in the form of six element MIMO antenna, there was an
increase in antenna gain from 7.66 dBi to 15.6 dBi while the suppression of the side lobes is -2.8 dB with
efficiency of -1.371. When elements were assembled in the form of eight element MIMO antenna, there was
an increase in antenna gain from 15.6 dBi to 16.8 dBi while the suppression of the side lobes is -2.7 dB with
efficiency of -1.393. When elements were assembled in the form of ten element MIMO antenna, there was an
increase in antenna gain from 16.8 dBi to 17.8 dBi while the suppression of the side lobes is -2.7 dB with
efficiency of -1.409. So we can conclude that there was an increase in antenna gain while addition of each
element antenna.

ACKNOWLEDGEMENTS

The authors would like to thanks to Ministry of Research, Technology and Higher Education
of the Republic of Indonesia for their research funding and Wireless Communication Centre (WCC),
Universiti Teknologi Malaysia for their support and collaboration.

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BIOGRAPHIES OF AUTHORS

Currently, Yusnita Rahayu is a senior lecturer and a researcher at Faculty of Engineering,
Universitas Riau (UR). She has been working for Universitas Riau since 2005 till now. She
graduated her B.Eng from Institute Science and Technology National (ISTN), Jakarta in 1999.
She finished her PhD from Universiti Teknologi Malaysia (UTM) in 2009 and graduated her
Master of Engineering (M.Eng) in 2004 at the same university. She has experiences for more
than 10 years in academic and research position at various international and national universities.
She has conducted various research projects from national and international grants. Her research
interest areas are such as radio transceiver design, antenna design, sensor networks, controlling
and monitoring system, IoT and wireless communication system. She has published more than
30 papers for national and international conference, 5 book chapters, 12 international journals.
She is also active as reviewer and technical program committee for various journals and
conferences. She is a senior member of IEEE and member of IEEE antenna & propagation
society.

Indah Permata Sari was born in Duri at 1997. She graduated her senior high school at SMAN 1
Mandau. Now, she is a student at Universitas Riau (UR) since 2015 till now in Department of
Electrical Engineering. Her interests are antenna design and wireless network.

High gain 5G MIMO antenna for mobile base station (Yusnita Rahayu)

ISSN: 2088-8708

Dara Incam Ramadhan is a student at Universitas Riau (UR) since 2015 till now in Department
of Electrical Engineering. She graduated her senior high school at SMAN 4 Duri. Her interests is
antenna design.

Assoc. Prof. Dr. Razali Ngah obtained his Bachelor in Electrical Engineering (Communication)
from Universiti Teknologi Malaysia, Skudai in 1989, MSc in RF Communication Engineering
from University of Bradford, UK in 1996 and PhD in Photonics from University of Northumbria,
UK in 2005. Since 1989, he has been with the Faculty of Electrical Engineering, UTM, where he
is currently a Senior Lecturer. Currently, he is an Associate Professor at Wireless
Communication Centre (WCC), Faculty of Electrical Engineering, UTM Skudai. His research
interests are Mobile Radio Propagation, Antenna and RF design, Photonics Network, Wireless
Communication Systems and Radio over Fibre (RoF). Dr. Razali had published more than 50
technical papers for journal and international conferences. His current focus is on his research
activity, internal audit committee of university and supervising Postgraduate and Undergraduate
students.

Int J Elec & Comp Eng, Vol. 9, No. 1, February 2019 : 468 - 476