A multiband high-isolation multiple-input multiple-output (MIMO) antenna using balanced mode and coupled neutralization line (NL) is presented in this article. The balanced modes of dipole and loop antennas, which leads to good isolation intrinsically are used for the 8 × 8 MIMO in the LTE bands 42 (3400-3600 MHz)/Chinese 5G band (3300-3400 and 3400-3600 MHz). The unbalanced mode of loop antennas, which optimized by decoupling structure are designed for the 4 × 4 MIMO in the LTE band 40 (2300-2400 MHz). Therefore, the eight-antenna array is formed by four dipole elements and four loop elements. The simulated and measured results show that the proposed antenna can cover 2300 to 2400 and 3300 to 3600 MHz, with reflection coefficient better than −6 dB and isolation higher than 15 dB. Good radiation performance and low envelope correlation coefficient can also be obtained. Specific absorption rate of user's hand is also discussed in this article. K E Y W O R D S5G smartphone, high isolation, MIMO, neutralization line decoupling, S-SAR | INTRODUCTIONAs the current 4G system can no longer meet the requirements of explosive communication data growth, 1-3 both industry and academia are focusing on realizing fifth generation (5G) communications. It has been proved that multipleinput and multiple-output (MIMO) antenna system can achieve large capacity and higher transmission rate for 5G systems below 6 GHz. [4][5][6][7][8][9][10][11][12][13][14][15][16] In the future, at least eight antenna elements should be integrated into a mobile terminal, which can achieve larger channel capacity and better communication reliability. Because of the trend of bezel-less screen design for cellphones, it is a big challenge to guarantee high isolation when more MIMO antenna elements are implemented in such small design space. 3 As the standard for 5G communication is now being formulated, some MIMO antennas designed for 5G smartphone
A dual-functional antenna array operating in the long term evolution (LTE) band 42 (3.4-3.6 GHz) and 5.8-GHz wireless wide area network (WLAN) band (5.725-5.875 GHz) for multipleinput multiple-output (MIMO) applications in 5G smartphones is proposed. The proposed 8-antenna array is composed of two different antenna elements, namely, the folded L-shaped antenna and couple-fed U-shaped antenna. It can be applied in the 8 × 8 (by using 8 antenna elements) and 4 × 4 (by using 4 antenna elements) MIMO system across the LTE band 42 and 5.8-GHz WLAN band, respectively. The quasi-orthogonal polarization, balanced mode excitation and pattern diversity are properly used to achieve high isolation within the operation bands. A prototype of the proposed antenna array was fabricated and measured. The measured isolations in the LTE band 42 (6-dB impedance matching) and 5.8-GHz WLAN band (10-dB impedance matching) are better than 17.1 dB and 34.6 dB, respectively. The total efficiencies are 45%-62% and 52%-59% in the two operation bands, respectively. Besides, the measured envelope correlation coefficients (ECCs) are less than 0.045 and 0.0001, the calculated peak ergodic channel capacities are 37.9 bps/Hz and 19.3 bps/Hz in the 8 × 8 or 4 × 4 MIMO system across the operation bands. Furthermore, user's hand and head effects are investigated and desirable results are obtained. The above results show that this proposed antenna array is a good candidate for MIMO applications in smartphones.
A dual-band eight-antenna array operating in the long-term evolution (LTE) band 41 (2.496-2.69 GHz) and 3.5-GHz band (3.3-3.7 GHz) for fifth-generation (5G) metalframed smartphone is presented. The proposed dual-band antenna array is composed of four identical dual-antenna building blocks (DABBs). Each DABB consists of two identical antenna elements with a neutralization line between them. The antenna array is simulated, fabricated, and measured. The isolations are better than 10.5 dB and 11.0 dB in the low band (LB; LTE band 41) and high band (HB; 3.5-GHz band). The total efficiencies are 41% to 54% and 46% to 64% in the two operation bands, respectively. In addition, the measured envelope correlation coefficients are less than 0.11 and 0.06, the calculated channel capacities are better than 34.5 and 36.3 bps/Hz in the LB and HB, respectively. Furthermore, four hand-grip scenarios are investigated, and results show that proposed antenna array can maintain excellent multipleinput multiple-output performances in all scenarios.Recently, metal-framed smartphones have been embraced by an increasing number of smartphones companies. The metal frame can increase the robustness and strength of the mobile handsets and allow the smartphone to have noble appearances. However, the metal frame can greatly affect the performance of antennas, such as the bandwidth and total efficiency. It poses a great challenge to the design of multiband smartphone antennas with integrated metal frame. As a key technique for 5G communications, the multiple-input multiple-output (MIMO) technology has become a hotspot both in academia and industrial community. MIMO technology has the potential to significantly enhance spectrum efficiency and channel capacity for the 5G communication system without consuming additional bandwidth or transmission power. 1,2 However, it is a challenging task to place multiple antennas in a limited design space while attaining wide bandwidths and desirable radiation performance.The sub-6 GHz bands (5G frequency bands below 6 GHz) are very important for 5G trails and future deployment. Recently, China's Ministry of Industry and Information Technology (MIIT) officially declared the 3.3 to 3.6 GHz frequency spectrum for 5G mobile communication. 3 In addition, South Korea and Australia chose the 3.55-GHz band (3.4-3.7 GHz) for future 5G communication network deployment. American reserved the 3.55 to 3.7 GHz band for future 5G communication spectrum deployment. 4 Among the frequency bands of sub-6 GHz, the long-term evolution (LTE) band 41 (2.496-2.69 GHz) is also a key candidate for 5G sub-6 GHz bands. Recently, it was adopted by the world's main communication equipment suppliers and operators as an existing band for 5G applications. 5 In recent works, some antenna array designs for 5G mobile devices utilize pattern diversity or orthogonal polarization technique to achieve good isolations and low correlations. [6][7][8][9] Other massive MIMO antenna array designs for smartphones applications are reported in References 10...
A wideband dual-polarized antenna is proposed for 4G and 5G communication applications. The antenna element consists of a pair of opened-loop dipoles for dual-polarization and its three inherent resonant modes are shifted closer to form a wide bandwidth. With additional U-shaped slots etched around the feed point, the input impedance of the antenna element is matched to 50 Ohm. The fabricated antenna element operates from 1.8 to 4.0 GHz, having 75.9% (VSWR ≤ 2) impedance bandwidth and high port-toport isolation (> 25 dB). It also achieves a 67±1 • beamwidth in H-plane and 68.7 ± 3.3 • in V-plane with 8.5 ± 1 dBi gain across the supported bands. By using six antenna elements and designing RF phase shifting module (RFPSM) based on vector modulators, a six-element dual-polarized array with electrically downtilt is also fabricated and measured, realizing a peak gain of 16.8 dBi, a similar beamwidth in H-plane as single antenna element and an electrically downtilt in V-plane from 0 • to 12 • which is preferred in communication applications. This antenna array could be used for future 5G communication and other applications. INDEX TERMS Wideband, dual-polarized, electrically downtilt, opened-loop dipoles, 5G.
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