Compact Omnidirectional 28 GHz 22 MIMO

Antenna Array for 5G Communications

Md Nazmul Hasan, and Munkyo Seo School of Electrical and Computer Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea

Email: nazmul@skku.edu, mkseo@skku.edu

Abstract - A compact 28 GHz planar monopole antenna is

presented. The proposed antenna consists of a triangular shape

radiator having exponentially tapered edges. The antenna exhibits a measured impedance bandwidth from 28.2 to 30.7 GHz. Measured radiation pattern confirms its omnidirectional

nature with linear polarization. Being compact, with an area of 1012 mm2, the proposed antenna can easily be integrated in handheld devices for 5G communications. Moreover, a 22

MIMO antenna array is presented, yielding a measured envelope correlation coefficient less than 0.001.

Index Terms — Millimeter-wave antenna, 28 GHz antenna,

monopole antenna, MIMO array, 5G antenna.

1. Introduction

With a hoard of new promising features, the realization of

fifth generation (5G) mobile communication is expected very

soon [1]. The 28 GHz band has the advantage of the least

path loss due to its relatively small atmospheric absorption,

compared to higher mm-wave 5G bands, such as 38 GHz, 60

GHz and 73 GHz [2]. Low profile, small antennas are the

best candidates for the integration in host devices. Besides,

in order to achieve higher data rate by virtue of spatial

multiplexing, the use of MIMO antenna array is fundamental.

A 28 GHz combined beam antenna having two main

radiators is reported in [3]. Another 28 GHz miniaturized

antenna (441.34 mm3) is reported in [4]. An inkjet-printed

antenna operating at 27.75 GHz is reported in [5].

This work presents a compact planar omnidirectional 5G

antenna operating over 28.2−30.7 GHz, with an area of

10×12 mm2. Moreover, a 2×2 MIMO antenna array has been

designed, fabricated and tested, yielding a measured

envelope correlation coefficient (ECC) less than 0.001 which

signifies very low mutual coupling between the two antenna

elements. The proposed antenna is small enough for

integration in hand-held devices and Internet of Things (IoT)

targeting 28 GHz 5G communications.

Detailed design of the proposed antenna is discussed in

section 2, followed by section 3 providing the results.

Section 4 elaborates MIMO antenna array design and

measurement results.

2. Antenna Design

The proposed antenna consists of a triangular shape

radiator with exponentially tapered edges as shown in Fig.

1(a). Partial ground plane, as shown in Fig. 1(b), is used to

achieve wide band impedance matching. Rogers RT/Duroid

5880 substrate having a thickness of 0.38 mm, relative

permittivity of 2.2, and loss tangent of 0.0009 is used to

fabricate the antenna. Fig. 1(c) illustrates the 3D model of

the proposed antenna with connector. The fabricated antenna

is shown in Fig. 1(d). Table I lists the dimensional

parameters of the antenna.

Fig. 1. (a) Top view, (b) bottom view, (c) 3D Model and (d)

photo of the proposed antenna.

TABLE I

Dimensional Parameters of the Proposed Antenna

Parameter Value

(mm)

Parameter Value

(mm)

Parameter Value

(mm)

W 12 i 0.5 j 0.25

L 10 n 3.88 v 0.86

m 1.52 Mw 0.66 G 6.66

3. Results

The proposed antenna was designed in HFSS, and

measurements were performed in anechoic chamber with

Agilent E8364B network analyzer. The measured impedance

bandwidth is from 28.2 to 30.7 GHz, as shown in Fig. 2. The

measured return loss has a slight shift, which is attributed to

fabrication tolerance and soldering. Fig. 3 shows the

radiation patterns in E-plane and H-plane at 28 GHz. Table II

compares the proposed antenna with other works. The

[WeD1-4] 2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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proposed antenna is more compact than [5], while offering

wider impedance bandwidth than [3] and [4].

Fig. 2. Reflection coefficient of the proposed antenna.

(a) (b)

Fig. 3. Radiation patterns (a) E-plane and (b) H-plane.

TABLE II

Comparison of the Proposed Antenna with Other Works

Reference Operating frequency (GHz) Size (mm3)

This work 28.2−30.70 10120.38

[3]a 27.47−28.45 441.34

[4]a 27.75 15.53.50.0685

[5]b 26.8−29 19.9300.79 a Simulation based work; b Waveguide size not included

4. 22 MIMO Antenna Array

Fig. 4. (a) Top view, (b) bottom view and (c) photo of the

proposed 2×2 MIMO antenna array.

Based on the proposed antenna, a 2×2 MIMO antenna

array has been designed, fabricated and tested. Fig. 4(a)

shows the top view, and Fig. 4(b) shows the bottom view of

the MIMO array, where Wx and Wy are 12 mm and 24 mm,

respectively. The fabricated MIMO array is shown in Fig.

4(c). The measured ECC is less than 0.001 as shown in Fig.

5, which indicates negligible mutual coupling between the

antennas. The calculation of ECC was performed using (1)

formulated by Blanch et al [6].

Fig. 5. Envelope correlation coefficient (ECC) plot.

|S*11S12+S*21S22|2

ECC = ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯ (1)

(1−(|S11|2+|S21|2)) (1− (|S22|2+|S12|2))

5. Conclusion

A planar omnidirectional miniaturized antenna operating

from 28.2 to 30.7 GHz is proposed. Additionally, a 2×2

MIMO antenna array with a measured ECC less than 0.001

is presented. The proposed antenna is suitable for 28 GHz

5G hand-held devices.

Acknowledgment

This research was supported by Basic Science Research

Program through the National Research Foundation (NRF)

of South Korea funded by the Ministry of Education (NRF-

2016R1D1A1B03934114).

References

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2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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