Coexist Design of Sub-6GHz and Millimeter-Wave Antennas ...

Coexist Design of Sub-6GHz and Millimeter-Wave Antennas for 5G Mobile Terminals

Zhouyou Ren, Shengjie Wu, and Anping Zhao

Advanced Technology Team Shenzhen Sunway Communication Co., Ltd.

Shenzhen 518057, China

Abstract – A compact coexist structure with both sub-6GHz antennas and millimeter-wave antennas is presented in this paper. The proposed antenna system has two 1×8 linear arrays for millimeter-wave system which cover 24.75-27.5GHz and a dual-band 8-antenna array for sub-6GHz system covers both 3.3-3.6GHz and 4.8-5.0GHz. The above frequency bands will be used in the future 5G communications. Simulation results show that both the systems can have good performance. Antenna prototype for sub-6GHz system is fabricated and measured; and quite good agreement between simulated and measured results is obtained.

Index Terms — 5G, 8-antenna array, millimeter-wave, mobile terminal antenna.

1. Introduction

It is getting closer and closer to the commercialization of the fifth generation (5G) communication with the explosive growth of new technology. For 5G wireless communication system, two main bands will be used including millimeter-wave band and the band below 6GHz. For the mm-wave system, the phased array antenna should be adopted to compensate the propagation loss [1]. And for the sub-6GHz system, in order to meet the requirement of the 5G transmission rate, the number of antennas should be over eight, that is, the 8×8 multiple-input and multiple-output (MIMO) antenna system will be used [2, 3]. In this paper, a coexist design with both the sub-6GHz and millimeter-wave antennas is proposed for the first time. The 8-antenna array for sub-6GHz system is operating in both 3.3-3.6GHz and 4.8-5.0GHz band with acceptable isolation better than 12dB among each antenna and total efficiencies better than 50%. Through the configuration of eight sub-6GHz antennas, enough space in the middle of mobile phones was remained for two 1×8 linear arrays of the millimeter-wave system. Good performance was obtained by CST software. All the antennas are placed perpendicular to the system ground plane of mobile phone, which makes it very suitable for the mobile terminals with full-display.

2. Antenna Element and Configuration

Fig. 1 shows the perspective and side views of proposed antennas used in mobile phone. All the antenna elements are symmetrically located along the two long sides of a 75mm ×136mm ground plane, which is nearly the same size as many latest flagship mobile devices. The eight antenna units

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Fig. 1. Perspective and side views of proposed antenna system. (a) perspective view and (b) side view.

(a) (b)

Fig. 2. Single antenna element with optimal parameters. (a) sub-6GHz antenna and (b) mm-wave antenna. of the sub-6GHz are printed on four small FR4 substrates (each small substrate consists of two antenna units) that are placed perpendicular to the system ground plane. The dimension of each small FR4 substrate is 46mm×5.5mm× 0.8mm, while the size of main FR4 substrate is 150mm× 75mm×0.8mm. All the FR4 substrates are double-sided with εr = 4.3 and tanδ = 0.02. The two clearance areas (75×7mm) located at both top and bottom of system substrate are reserved for the 4G LTE and other antennas used in current mobile handsets. In addition, on each side of the mobile phone, a small double-sided PCB made of Rogers material (thickness = 0.25mm, εr = 3.0, tanδ = 0.0013) with a length of 44mm located between the two small FR4 substrates is used to place the 1x8 millimeter-wave linear array.

Fig. 2(a) shows the single unit of sub-6GHz antenna. The antenna unit is composed of a U-shaped element and a Z-shaped monopole antenna printed separately on the different

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

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sides of the FR4 substrate; and the entire bottom of the U-shaped element is connected to the ground and the Z-shaped monopole antenna is fed by a 50Ω microstrip line. Fig. 2(b) illustrates the single millimeter-wave antenna element. This antenna is a variant of dipole antenna, and its arms consist of two right triangles. One of the arms is connected to the 50Ω microstrip line, and another is connected to the PCB ground through vias. The gradual arms structure can increase the bandwidth of the antenna. The mm-wave antenna array consists of eight antenna elements, and the distance between two adjacent elements is 5.35mm which is about 0.47λ at 26GHz. Three stages of micro-strip T-junction splitters are used as feeding network for the array and all the antennas in the system share the same ground.

3. Simulated and Measured Results

(1) Dual-band Sub-6GHz MIMO System As shown in Fig. 3, a prototype of the 8-antenna array of

the sub-6GHz system was fabricated and measured. The measured and simulated S-parameters are plotted in Fig. 4(a). It clearly shows that the antennas can cover both 3.3-3.6GHz and 4.8-5.0GHz bands with isolations better than 12dB. The total efficiencies of the antennas, as shown in Fig. 4(b), are over 50% in both the bands. Quite good agreement between measurement and simulation is obtained. Fig. 5(a) shows the envelop correlation coefficient (ECC) values, which are all less than 0.05 and thus can meet the needs of 5G application.

Fig. 3. Photo of the fabricated antenna prototype of the sub-6GHz 8×8 MIMO antenna system.

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Fig. 4. Simulated and measured results for the 8×8 MIMO antenna system. (a) S-parameter and (b) total efficiency.

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Fig. 5. Simulated results for the 8×8 MIMO antenna system. (a) envelope correlation coefficient and (b) channel capacity.

The channel capacity (CC) is also calculated with the formulator used in [4]; and the result in Fig. 5(b) is obtained by averaging over 10,000 Rayleigh fading realizations with 20dB SNR. The calculated channel capacities in both the 3.5GHz and 4.9GHz bands all reach 35bps/Hz, where the ideal CC of the 8x8 MIMO system is about 44bps/Hz.

(2) 1×8 Linear Array for Millimeter-Wave System The simulated S-parameter and total efficiency of the 1×8

linear array (indicated as port 10) is shown in Fig. 6(a). It can be seen from Fig. 6(a) that the 10dB impedance bandwidth for S10,10 is from 23.4GHz to 29GHz and the total efficiency is better than 90%. Thus, it can cover the 5G mm-wave band (24.75GHz - 27.5GHz) proposed by the Ministry of Industry and Information Technology (MIIT) of China. It is worth noting that the sub-6GHz antenna has almost no impact on the mm-wave antenna array (isolation better than 30dB). Fig. 6(b) shows that the maximum realized gain of the 3D pattern at 26GHz (with scanning angle = 0 degree) is about 12.2dBi.

(a) (b)

Fig. 6. Simulated results for 1×8 linear array. (a)S-parameter and efficiency; (b) 3D pattern at 26GHz.

4. Conclusion

A coexist antenna design which can cover 3.3-3.6GHz, 4.8-5.0GHz and 24.75-27.5GHz for 5G mobile handsets is presented. Simulated and measured results indicate that the proposed antenna system has not only compact size but also good antenna performance; and it is a good candidate for the 5G application in mobile terminals.

Acknowledgment

The authors would like to thank the Shenzhen Science and Technology Innovation Committee, China for the financial support under Key Project 2017-0237.

References

[1] A. Zhao, F. Ai, “Dual-band 5G millimeter-wave MIMO antenna array for mobile phone application,” 2018 12th European Conference on Antennas and Propagation, paper T01-13.2, London, April 9-13, 2018.

[2] M. Y. Li, Y. L. Ban, Z. Q Xu, G. Wu, C. Sim, K. Kang, and Z. F. Yu, “Eight-port orthogonally dual-polarized antenna array for 5G smartphone applications,” IEEE Trans. Antennas Propag., vol. 64, no. 9, pp. 3820–3830, Jun. 2016.

[3] Y. L. Ban, C. Li, C. Y. D. Sim, G. Wu, and K.-L. Wong, “4G/5G multiple antennas for future multi-mode smartphone applications”, IEEE Access, vol. 4, pp. 2981-2988, July 2016.

[4] J. X. Yun and R. G. Vaughan, “Multiple element antenna efficiency and impact on diversity and capacity,” IEEE Trans. Antennas Propag., vol. 60, pp. 529-539, Feb. 2012.

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

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