An antenna decoupling method based on modal control is proposed in this paper. Different from the previous characteristic mode decoupling methods, which excite one of the characteristic modes from each port, a pair of decoupling modes is excited simultaneously at each port. To validate our method, a head-tohead antenna pair is analyzed and designed. According to the characteristic mode analysis, an inductor-loaded coupled sheet is introduced for the head-tohead antenna pair. Thus, the resonant frequencies of decoupling modes can be tuned individually. To further demonstrate the flexibility of our design, an eightelement multiple-input multiple-output (MIMO) antenna composed of two integrated four-element blocks is designed, fabricated, and measured. The proposed antennas show good impedance matching, isolation, and diversity performance varying from 3.35 to 3.71 GHz. Both simulated and measured results show the 8 Â 8 MIMO system can achieve isolations of better than 11.5 dB and envelope correlation coefficients of less than 0.2 of each port.
The demand for a high transmission data rate in 5G leads to the wide application of the multi‐input, multi‐output (MIMO) technique. However, the narrow design space in mobile phone causes severe unexpected coupling between antenna units and deteriorate the system performance dramatically. In this paper, we focus on the antenna coupling within the MIMO system. Some decoupling techniques are summarized, such as neutralization line, decoupling network, common/differential mode cancellation, etc. Finally, new decoupling research developments of modal currents cancellation based on the theory of characteristic mode are elaborated. Two design examples are shown to validate the benefit of the proposed decoupling method. The −6 dB impedance bandwidth of the head‐to‐head antenna pair can cover 3.4–3.6 GHz. The isolation level is improved from more than 3.7 dB to more than 13 dB. The tail‐to‐tail antenna pair can cover 3.3–5 GHz and the isolation level is improved from more than 5 dB to more than 10 dB in the whole operating bandwidth. Both antenna pairs can achieve an envelop correlation coefficient of less than 0.2 and the antenna efficiencies are more than 40%.
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