In this paper, an eight-element MIMO array for 5G smartphone applications in the 3. GHz) is presented. The array consists of two types of four-antenna arrays (U-shaped and L-shaped coupled-fed loop elements), which are symmetrically distributed in the inner of the smartphone frame. The dimension of the system circuit board is 124 mm × 74 mm and the size of two elements is 4.8 mm × 9.8 mm (0.055λ × 0.11λ, λ represents the free-space wavelength at 3.45 GHz) and 4.9 mm × 12.5 mm (0.056λ × 0.14λ), respectively. The proposed MIMO array is simulated, and a prototype is fabricated and tested. The results show that all the elements can cover the desired band of 3.3-3.6 GHz under the condition of −6-dB impendence bandwidth. The isolations are enhanced to 15 dB by combining the inverted-I ground slots with neutralization line (NL) structure. In addition, the envelope correlation coefficient (ECC) via any two elements is below 0.15 that shows good independence in far-field radiation characteristic. The measured efficiencies of the elements in the operating band are higher than 40%. Moreover, the array ergodic channel capacity is also calculated based on the correlation matrix method to be about 35 bps/Hz with a 20-dB signal-to-noise ratio. In addition, the effects of the user's hand and the head has been analyzed as well. Based on the above, the proposed eight-element MIMO array is a prospective candidate for future 5G smartphone applications.INDEX TERMS Channel capacity, eight-element array, high isolation, MIMO antenna.

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In this paper, a compact dual-band MIMO antenna array for 5G smartphone applications is proposed. The MIMO antenna consists of eight folded monopole antennas operating at 3.45-GHz band (3300∼3600MHz). And the antenna elements with a size of 6.8 × 6.6 × 4 mm 3 (about 0.078λ× 0.075λ× 0.046λ at 3.45 GHz), are disposed along each edge of the system circuit board. By introducing the decoupling structures, the isolation between inner antenna elements is improved from 10dB to 15.1dB in 3.45-GHz band (3300∼3600MHz). Meanwhile the inner antenna units can generate an additional operating band covering 2400∼2700MHz due to the coupling effect between the antenna elements and the proposed decoupling structures, which is promising for solving the problem of terminal space shortage. To verify the design principle of the proposed MIMO antenna array, the antenna is fabricated and measured. The measured results of efficiency and ECC are analyzed as well to demonstrate the performance of the proposed MIMO array. Channel capacity, user proximity and SAR analysis and are also given in this paper.INDEX TERMS Decoupling structure, eight-element array, high isolation, MIMO antenna.

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) array using a multi-slot decoupling technique for the fifth generation (5G) mobile communication. By employing a compact dual-loop antenna element, the proposed array obtains two broad bandwidths of 12.2% and 15.4% for sub-6GHz operation. To reduce the mutual coupling between antenna elements, a novel dualband decoupling method is proposed by employing a multi-slot structure. The proposed MIMO array achieves 15.5-dB and 19.0-dB isolations across the two operating bands. Furthermore, three decoupling modes generated by different bent slots can be independently tuned. Zero ground clearance is also realized by the coplanar arrangement of the antenna elements and decoupling structures. The proposed MIMO array was simulated, fabricated, and measured. Experimental results agree well with the simulations, showing that the dual-band MIMO array has good impedance matching, high isolation, and high efficiency. In addition, the envelope correlation coefficient and channel capacity are calculated and analyzed to validate the MIMO performance of the 5G terminal array. Such a dual-band high-isolation eight-element MIMO array with zero ground clearance is a promising candidate for 5G or future mobile applications. INDEX TERMS Dual-band decoupling, fifth generation (5G) communication, MIMO antenna, smartphone antenna.

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A printed microstrip-line-fed slot antenna with a pair of parasitic patches for bandwidth enhancement is proposed in this paper. By using the parasitic patches along the microstrip feed line, an additional resonance is excited and a good performance of bandwidth enhancement can be obtained. The proposed antenna is designed and manufactured successfully. The measurement shows a good agreement with the simulation. From the measured results, the enhanced impedance bandwidth, defined by voltage standing wave ratio (VSWR) less than 2, is about 136% ranging from 2.1 to 11.1 GHz. In addition, stable and nearly omnidirectional far-field radiation patterns are observed over the entire operating band.Index Terms-Bandwidth enhancement, microstrip-line-fed antenna, printed slot antenna, parasitic patch.