Abstract
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 $37.2\times7$ mm2 consists of two identical $13.6\times7$ mm2 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.
Highlights
The desire for a high data-transmission rate in the fifthgeneration (5G) mobile communications has fueled the need for the multiple-input multiple-output (MIMO) antenna systems that can provide large transmission volumes and high transmission rates
Many densely deployed multi-input multi-output (MIMO) antenna systems have been proposed for mobile communications in recent years [1]–[12]. These MIMO antenna systems are mounted on some different mobile communication devices, the design goal of incorporating in a limited space as many antenna elements as possible for faster transmission is the same
In [1]–[3], the antenna elements in a 5G MIMO antenna system mounted in a smart phone were spaced by a distance of as large as 10–30 mm
Summary
The desire for a high data-transmission rate in the fifthgeneration (5G) mobile communications has fueled the need for the multiple-input multiple-output (MIMO) antenna systems that can provide large transmission volumes and high transmission rates. Two ungrounded narrow strip resonators in the MIMO antenna system can enhance the simulated intra-unit isolations by about 3.5 dB at the mid-band frequency. Intra-unit isolations at 3.5 GHz (the mid-band frequency) for the first and second dual-slot-antenna units are as small as only 6.67 and 6.43 dB, respectively The ungrounded strip resonators trade a wider operating band for a narrower but still acceptable one and, most importantly, satisfying isolations, which are desirable results making the dual-slot-antenna units meet the MIMO operation criteria. The surface electric currents shown in this figure serve as another proof that the ungrounded full-wavelength strip resonator can effectively improve the intra-unit isolation
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