Abstract
This paper proposes a small-slot antenna system (50 mm × 9 mm × 2.7 mm) for 4 × 4 multiple-input multiple-output (MIMO) on smart glasses devices. The antenna is set on the plastic temple, and the inverted F antenna radiates through the slot in the ground plane of the sputtered copper layer outside the temple. Two symmetrical antennas and slots on the same temple and series capacitive elements enhance the isolation between the two antenna ports. When both temples are equipped with the proposed antennas, 4 × 4 MIMO transmission can be achieved. The antenna substrate is made of polycarbonate (PC), and its thickness is 2.7 mm εr=2.85, tanδ=0.0092. According to the actual measurement results, this antenna has two working frequency bands when the reflection coefficient is lower than −10dB, its working frequency bandwidth at 4.58–5.72 GHz and 6.38–7.0 GHz. The proposed antenna has a peak gain of 4.3 dBi and antenna efficiency of 85.69% at 5.14 GHz. In addition, it also can obtain a peak gain of 3.3 dBi and antenna efficiency of 82.78% at 6.8 GHz. The measurement results show that this antenna has good performance, allowing future smart eyewear devices to be applied to Wi-Fi 5G (5.18–5.85 GHz) and Wi-Fi 6e (5.925–7.125 GHz).
Highlights
Smart wearable devices that are compact, lightweight, and ergonomic are quickly becoming mainstream
The inverted-F antenna is manufactured by Laser Direct Structuring (LDS) on the inner side of the temple with a substrate made of polycarbonate (PC)
In the multiple-input multiple-output (MIMO) antenna system, when port 1 is excited and other ports are connected to a 50-ohm load, the far-field radiation direction generated by antenna 1 can be represented by F 1 (θ, φ)
Summary
Smart wearable devices that are compact, lightweight, and ergonomic are quickly becoming mainstream. For fifthgeneration (5G) mobile communications and Wi-Fi 6 wireless indoor communications, more antennas are needed to support the ultra-high broadband transmission rate in the ultrahigh-frequency band and better transmission path reliability. It will be a major challenge for antenna researchers to set up a MIMO antenna system with high isolation in space-constrained smart wearable devices, and an asymmetrical antenna architecture can compensate for the problem of poor isolation [14,15,16,17,18].
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