Compact Quad-Offset Loop/IFA Hybrid Antenna Array for Forming Eight 3.5/5.8 GHz MIMO

Antennas in the Future Smartphone

Wei-Yu Li1, Wei Chung1, Kin-Lu Wong2 1ICL, ITRI, Hsinchu 31057, Taiwan

2Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung 80424, Taiwan

Abstract –This article presents a novel dual-band eight-antenna array for future mobile and WLAN MIMO networks applications in a smartphone. It is formed by two compact quad-offset loop/IFA hybrid antenna arrays disposed along two long side edges of a PCB ground plane for 3.5/5.8-GHz bands operations. The proposed quad-offset antenna array as a decoupled dual-band building block has a compact planar size of 7 × 34 mm2 only, the occupied lateral length of which along the side edge is only about 0.396 wavelength (34 mm) at 3.5 GHz. The experiment results show good impedance matching and low correlation characteristics in the both desired 3.5/5.8-GHz bands for the proposed 8-antenna array. The constructed prototype has been studied in this paper.

Index Terms — MIMO antennas, smartphone antennas, eight-antenna array, compact decoupled building block.

1. Introduction

Multi-input multi-output (MIMO) operation has been known to be very promising for the upcoming fifth-generation (5G) communication system applications [1-3]. And by integrating a large number of MIMO antennas in the mobile device, it can provide high-dimensional MIMO operation with a much higher channel capacity and data throughput for the mobile users [1-3]. Therefore, a challenge task for embedding multiple MIMO antennas in a practical mobile phone with limited available space has attracted great attention in recent years [1-3]. In prior studies, eight or sixteen MIMO antennas integrated in a smartphone for covering single 3.5 GHz band of global mobile broadband service operations have been reported [1-2]. And in Ref. [3], a compact decoupled dual-band two-antenna building block has been presented for forming eight MIMO antennas in a smartphone to cover both 3.5-GHz band (3400-3600 MHz) of 5G mobile network and 5.8-GHz band (5725-5875 MHz) of WLAN MIMO operations. In Ref. [3], two dual-band two-antenna building blocks are disposed along the same long side edge of PCB to form a quad-antenna array with an overall occupied planar size of 7 × 45 mm2 (lateral length 45 mm), and by symmetrically implementing another quad-antenna array at the other long side edge of PCB to form the eight MIMO antennas [3]. In this article, a novel dual-band quad-offset loop/IFA hybrid antenna array with a more compact planar size of 7 × 34 mm2 only is presented. And an eight-antenna array prototype capable of 3.5/5.8-GHz bands MIMO

operations is implemented by utilizing the proposed quad-offset hybrid antenna array technology.

2. MIMO Antenna Array Design

Fig. 1 shows geometry of the constructed 3.5/5.8 GHz dual-band eight-antenna array prototype for MIMO operations which is formed by two proposed compact quad-offset loop/IFA hybrid antenna arrays (Ant1 to Ant4 and Ant5 to Ant8) symmetrically disposed along two long side edges of the PCB ground plane. The proposed quad-offset antenna array mainly consists of four loop/IFA hybrid antennas, such as Ants 1, 2, 3, 4. The hybrid antenna has a coupled-feeding portion, a grounding strip and a bended radiating strip. In the relatively lower frequencies, the coupled-feeding portion, the grounding strip and the adjacent side edge of ground plane can form a 0.25λ loop resonant path [3] successfully to generate operating mode for covering the 3.5 GHz band. In the higher frequencies,

Fig. 1. Geometry of the constructed 3.5/5.8-GHz dual-

band eight-antenna array prototype for MIMO operations.

[ThD1-1] 2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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Fig. 2. Simulated current distribution and measured S parameters of the quad-offset loop/IFA antenna array.

the hybrid antenna performs as a bended IFA architecture. In that situation, the coupled-feeding portion and the grounding strip would become equivalent feeding and matching circuit of the bended radiating strip to generate a 0.25λ resonant mode for covering the higher 5.8 GHz band. And for decoupling considerations, the grounding strips of the four hybrid antennas must be arranged to face each other. Besides, the loop/IFA hybrid antennas disposed at different side spaces of the ground edge (such as Ants 1, 2 at the same side space and Ants 3, 4 at the other side space) need to be asymmetrical-offset arrangement. The proposed quad-offset antenna array has a compact planar size of 7 × 34 mm2 only, and can be closely integrated at the ground side edge with a small protruded distance of 1 mm only.

3. Results and Discussion

Fig. 2 shows the simulated current distribution and measured S parameters of the quad-offset loop/IFA hybrid antenna array (Ant1 to Ant4). It can be seen that the 0.25λ loop modes and the 0.25λ IFA modes of the four hybrid antennas (Ant1 to Ant4) can be generated successfully with good impedance matching and isolation for separately covering 3.5-GHz band (3400-3600 MHz) and 5.8-GHz band (5725-5875 MHz) operations. And from the measured and calculated results shown in Fig. 3, it can be seen that the measured antenna efficiencies and ECCs (envelope correlation coefficients) are better than 38% and less than 0.35 in the lower 3.5 GHz band, and are better than 45% and less than 0.25 in the lower 5.8 GHz band. The performances of the other quad-offset antenna array (Ant5 to Ant8) are similar to the results shown in Figs. 2 and 3. And the proposed eight-antenna array can achieve

Fig. 3. Measured antenna efficiency and calculated ECC from the measured complex electric-field patterns. low correlation characteristics in the both desired 3.5/5.8-GHz bands. More detail analysis including channel capacity and the throughput of the proposed dual-band eight MIMO antennas in an 8 × 8 MIMO system will be presented and discussed in the conference.

4. Conclusion

A novel dual-band eight-antenna array for future mobile and WLAN MIMO networks applications in a smartphone has been presented. The experiment results show good impedance matching and low correlation characteristics in the desired 3.5/5.8-GHz bands. It is formed by two compact quad-offset loop/IFA hybrid antenna arrays disposed along two long side edges of the ground plane. The proposed quad-offset antenna array has a compact planar size of 7 × 34 mm2 only, and can be closely integrated at the ground side edge with a small protruded distance of 1 mm only. Therefore, it can also be suitable for the wide-size screen smartphone applications.

References

[1] Kin-Lu Wong, Jun-Yu Lu, Li-Yu Chen, Wei-Yu Li, Yong-Ling Ban, “8-antenna and 16-antenna arrays using the quad-antenna liner array as a building block for the 3.5-GHz LTE MIMO operation in the smartphone,” Microwave Opt. Technol. Lett., Vol. 58, pp.174-181, Jan. 2016.

[2] Kin-Lu Wong, Jun-Yu Lu, Li-Yu Chen, Wei-Yu Li, Young-Ling Ban, Chuan Li, “16-antenna array in the smartphone for the 3.5-GHz MIMO operation,” IEEE Asia-Pacific Microwave Conference, Dec. 2015.

[3] Kin-Lu Wong, Bo-Wei Lin, Wei-Yu Li, “Dual-band dual inverted-F/loop antennas as a compact decoupled building block for forming eight 3.5/5.8-GHz MIMO antennas in the future smartphone,” Microwave Opt. Technol. Lett., Vol. 59, pp. 2715-2721, Nov. 2017.

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

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