Compact Wideband MIMO Antenna for 5G Communication Fei Wang, Zhaoyun Duan*, Qian Li, Yanyu Wei, Yubin Gong School of Physical Electronics University of Electronic Science and Technology of China Chengdu, China [email protected], [email protected]*, [email protected], [email protected], [email protected] Abstract—In this paper, we propose a compact wideband antenna. The operation band of the antenna covers from 3 GHz to 30 GHz with dimensions of 25 mm× 25 mm. The measured antenna S-parameters are in good agreement with the simulated ones. Furthermore, based on the proposed wideband antenna, a two-element multiple-input-multiple-output (MIMO) antenna with high isolation is developed due to its orthogonal polarization directions. Due to the advantages such as wide bandwidth, compact structure, and high isolation, this MIMO antenna is suitable for the 5th generation (5G) communication. II. To realize a wide bandwidth, we have improved the monopole antenna. The original prototype of the monopole antenna is presented in Fig. 1 (a). It’s a square monopole antenna with coplanar waveguides (CPW) feedline. The antenna is printed on FR4 substrate with relative permittivity of 4.4 and loss tangent of 0.06. The size of the antenna is 25 mm× 25 mm× 1 mm. By using the HFSS, we obtain the simulated S11 parameters of the original monopole antenna, as shown in Fig. 1 (c). It can be observed that the operation band of this antenna covers from 3 GHz to 11 GHz. Keywords—5G communication; microstrip antenna; MIMO I. WIDEBAND ANTENNA DESIGN INTRODUCTION The improved monopole antenna is shown in Fig. 2 (a). The slots 1 and 2 on the top side of the antenna and triangle slots 3 and 4 on the sides of the antenna patch have been added to extend the operation band of the antenna. The width of the slots 1 and 2 are 2 mm and 1 mm, respectively. The S11 parameters of the antenna are illustrated in Fig. 1 (c). From Fig. 1 (c), we can see that the antenna operation band has been extended as 3 GHz to 20 GHz. Recently, the wireless communication technology is facing the explosively increasing demands of high transmission rate, stable communication quality, and complex application scenarios. These demands have triggered the research of the 5th generation (5G) cellular network in the world , . Compared with the current wireless communication technologies, the higher technical indexes lead to a wider operation band of the 5G communication. In addition, the lower frequency bands, especially under 3 GHz, are saturated with all kinds of existing communication technologies ,  which cannot fulfill the requirements of 5G communication. Therefore, current research about 5G communication is mainly focused on the frequencies from 3 GHz to 30 GHz , . As one of the most important components of the 5G communication, the multiple-input-multiple-output (MIMO) antennas for 5G communication have been widely studied , . Since the miniaturization has become the trend of wireless communication, the size of the antenna must be small enough to be integrated with other components. Therefore, realizing wide band MIMO antenna in the limited space is a big challenge for all the antenna researchers. (a) (b) 0 S11 (dB) -10 Focusing on these problems, we propose a compact wideband antenna which is suitable for 5G communication. Considering the compatibility of different wireless communication modes, the operation band of the wideband antenna is designed to be from 3 GHz to 30 GHz. Based on it, a two-element MIMO antenna has been proposed using orthogonal polarization. The proposed MIMO antenna can realize a high isolation between antenna elements in the operation band without increasing its size. -20 -30 Without slots With slots -40 -50 -60 5 10 15 Frequency (GHz) 20 25 (c) Fig. 1. Dimensions of the antennas without slots (a) and with slots (unit: mm) (b), simulated S11 parameters of the antennas without and with slots (c). This work was supported in part by the National Natural Science Foundation of China (Grant Nos. 61471091, 61611130067, and 61531010). 978-1-5386-3284-0/17/$31.00 ©2017 IEEE 939 AP-S 2017 To further extend the operation bandwidth, the antenna has been designed as shown in Fig. 2 (a). A trapezoid patch (the purple part in Fig. 2 (a)) is added on the back side of the antenna which can couple the energy at higher frequency from the feed line without influencing the performance at lower frequency. The winglike structure on the two sides of the antenna can couple energy from back side patch to make operation band cover from 3 GHz to 30 GHz. In order to validate the present approach, the proposed antenna is fabricated, as shown in Fig. 2 (b). The measured S11 performance is presented in Fig. 2 (c) and compared with the simulated results. From Fig. 2 (c), it is obvious that the antenna operates from 3 GHz to 30 GHz which shows in good agreement with the simulation. (a) S-parameters (dB) 0 -10 -20 -30 S21 -40 -50 S11 5 10 15 20 Frequency (GHz) 25 30 (b) Fig. 3. MIMO antenna geometry (a) and its S-parameters (b). IV. (a) (b) 0 S11 (dB) -10 -20 -30 Measured Simulated -40 -50 5 10 15 20 25 Frequency (GHz) 30 35 (c) Fig. 2. Dimensions of the wideband antenna (unit: mm) (a) and its fabricated prototype (b); simulated and measured S11 parameters of the antenna (c). III. CONCLUSION In this talk, we propose a compact wideband antenna. Through adding slots on the antenna patch and adding extra radiation patch on the back side, the proposed antenna has an ultra-wide operation bandwidth (3 GHz–30 GHz) with a compact structure (25 mm 25 mm). The experimental results agree well with the simulated ones. Based on this wideband antenna, we develop a two-element MIMO antenna. Since the polarization directions of the two antenna elements are orthogonal, the coupling between the two elements has been reduced. This finding is verified from the simulated results. The proposed MIMO antennas have potential applications in miniaturized 5G communication devices. REFERENCES  MIMO ANTENNA DESIGN Based on the above work, a two-element MIMO antenna has been developed as shown in Fig. 3 (a). The MIMO antenna consists of two same antenna elements, one of them has been rotated 90 degrees to make sure that the polarization direction of the two antenna elements are orthogonal. Therefore, the coupling between two antenna elements has be reduced without extending the space between them.  We use the HFSS to simulate the S-parameters of the MIMO antenna, as shown in Fig. 3 (b). It can be observed that the S21 parameter maintains under -20 dB which means the high isolation between two antenna elements. Besides, compared with Fig. 2 (c), the influence on the antenna return loss is negligible.       940 T. S. Rappaport, S. Sun, R. Mayzus, and H. Zhao, “Millimeter wave mobile communications for 5G cellular: It will work!,” IEEE Access, vol. 1, pp. 335–349, 2013. E. Hossain and M. Hasan, “5G cellular: Key enabling technologies and research challenges,” IEEE Instrum. Meas. Mag., vol. 18, pp. 11–21, June 2015. F. Wang, Z. Y. Duan, T. Tang, M. Z. Huang, Z. L. Wang and Y. B. Gong, “A new metamaterial-based UWB MIMO antenna”, in IEEE IWS 2015, Shenzhen, China, pp. 1-4, Apr. 2015. A. Rajagopalan, G. Gupta, A. S. Konanur, B. Hughes, and G. 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