Antenna Decoupling Based on Characteristic Modes Cancellation

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%.