Compact Sub-6-GHz Four-Element MIMO Slot Antenna System for 5G Tablet Devices

A sub-6-GHz four-element multi-input multi-output (MIMO) slot antenna system was proposed in this study for fifth-generation (5G) tablet computers, where each antenna element was constructed using a slot structure. To effectively use the available space in a tablet and maximize the screen, we have deployed the MIMO antenna system on the left side-edge frame of the tablet. The MIMO antenna system measuring 37.2 x 7 mm(2) consists of two identical 13.6 x 7 mm(2) dual-slot-antenna units that are separated by 10 mm. The two closely spaced slot antennas in the same dual-slot-antenna unit are arranged asymmetrically mirrored of each other with respect to the system ground plane. Although the dual-slot-antenna unit is very compact, the isolation between the two slot antennas in the same unit can be enhanced by using an ungrounded full-wavelength strip resonator. With the two ungrounded resonators in the MIMO slot antenna system, the simulated intra-unit isolations at the mid-band frequency can be enhanced by about 3.5 dB to meet the design requirement. As a byproduct, the two ungrounded resonators in the MIMO antenna system can also enhance the simulated mid-band antenna efficiency by about 4.5% and lower the worst simulated ECC by 0.195, from 0.518 to 0.323. This MIMO antenna system can support the frequency band of 3400-3600 MHz for 5G. In the operating band, the measured isolation is larger than 11 dB, and the measured antenna efficiency is larger than 40%. The envelope correlation coefficients (ECCs) calculated from the measured complex E-field radiation patterns are all smaller than 0.23, making the proposed design suitable for 5G mobile communications that require fast transmission.