A hybrid antenna is proposed for future 4G/5G MIMO (multiple input multiple output) applications. The proposed antenna is composed of two antenna modules, namely, 4G antenna module and 5G antenna module. The 4G antenna module is a two-antenna array capable of covering the GSM850/900/1800/1900, UMTS2100, and LTE2300/2500 operating bands, while the 5G antenna module is an 8-antenna array operating in the 3.5 GHz band capable of covering the C band (3400-3600 MHz), which could meet the demand of future 5G application. Compared with ideal uncorrelated antennas in an 8 × 8 MIMO system, the 5G antenna module has shown good ergodic channel capacity of approximately 40 bps/Hz, which is only 6 bps/Hz lower than ideal case. This multi-mode hybrid antenna is fabricated, and typically experimental results such as S-parameter, antenna efficiency, radiation pattern, and envelope correlation coefficient (ECC) are presented.

A dual-polarized hybrid 8-antenna array operating in the 2.6-GHz band (2550-2650 MHz) for 5G communication multi-input multi-output (MIMO) operation in the smartphone is presented. The proposed hybrid antenna array elements are symmetrically placed along the long edges of the smartphone, and they are composed of two different 4-antenna array types (C-shaped coupled-fed and L-shaped monopole slot) that exhibit orthogonal polarization. Therefore, coupling between the two antenna array types can be reduced, and the MIMO system performances are enhanced. A prototype of the proposed 8-antenna array is manufactured and measured. Good impedance matching (10 dB return loss or better), desirable cross polarization discrimination (XPD better than 15 dB) and acceptable isolation (better than 12.5 dB) are obtained. Envelope correlation coefficient (ECC) and channel capacity are also calculated to evaluate the MIMO performances of the proposed antenna array.

Using the quad‐antenna linear (QAL) array as a building block, the 8‐antenna and 16‐antenna arrays for the 3.5‐GHz long term evolution multiple‐input multiple‐output (MIMO) operation in the smartphone are demonstrated. The QAL array has a planar structure of narrow width 3 mm (0.035λ) and short length 50 mm (0.58λ), with λ being the wavelength at 3.5 GHz. For the 8‐antenna array, two QAL arrays are disposed along two opposite side edges (denoted as Array A) or the same side edge (denoted as Array B) of the system circuit board of the smartphone. The obtained envelope correlation coefficient values of the antennas in Array A and B are shown. The calculated channel capacities for Array A and B applied in an 8 × 8 MIMO system are also analyzed. The 16‐antenna array formed by four QAL arrays disposed along two opposite side edges (denoted as Array C) is then studied. For operating in a 16 × 16 MIMO system, the calculated channel capacity of Array C can reach about 66–70 bps/Hz with a 20‐dB signal‐to‐noise ratio. The obtained channel capacity is about 5.7–6.1 times that (11.5 bps/Hz) of the upper limit of an ideal 2 × 2 MIMO system with 100% antenna efficiency for the antennas therein. Details of the proposed Array A, B, and C are described, and the obtained results are presented. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:174–181, 2016

An eight‐port antenna array designed for future 5G 2.6 GHz band (2550–2650 MHz) for multi‐input multi‐output (MIMO) in the smartphone applications is presented. In order to enhance the port isolation and reduce correlation between antennas, square loop radiating strip with orthogonal polarisation is employed. The proposed antenna array is composed of four pairs of uniform antenna elements that are symmetrically placed at the four corners of the main board, and each antenna pair includes a communal square loop and two independently coupled feeding strips. By exciting the square loop from the two feeding strips, respectively, two orthogonally polarised waves are generated. Thus, four horizontally polarised and four vertically polarised antennas are achieved in total. Due to this feature, coupling between antenna pairs is reduced and the MIMO performances are enhanced. A prototype of the proposed antenna array was fabricated, and the experimental results show good impedance matching and acceptable isolation measured across the bands of interest. The MIMO performances such as envelope correlation coefficient, mean effective gain, multiplexing efficiency and channel capacity are also calculated. Besides, simulations of the antenna shifted to 3.5 GHz are also performed. The consistent performances indicate that the proposed structure has good scalability and is promising for future 5G smartphone applications.

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