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 mm 2 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 mm 2 (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 mm 2 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 179