An efficient antenna mutual coupling reduction (decoupling) technique using reactively loaded dummy element array for two dual-band closely coupled MIMO antennas is proposed in this paper. This dummy element array comprises three dummy elements, including one low-frequency dummy element and two symmetrically placed high-frequency dummy elements. A pair of dual-band antennas working at 2.45 GHz (low band) and 5.8 GHz (high band) simultaneously is used to demonstrate the effectiveness of the proposed method and to illustrate the decoupling design process. The dual-band antennas with and without the designed dummy element array are both fabricated and measured. Measurement results show good impedance matching for both antenna ports at both operating bandwidths. More importantly, the isolations have been improved from 9 dB at low band and 7.7 dB at high band to more than 20 dB at low band and more than 25 dB at high band, respectively. The envelop correlation coefficient (ECC) as one key figure of merits for MIMO antennas is also improved significantly. The proposed method can find plenty of applications in dual-band wireless systems where multiple antennas are installed. INDEX TERMS Envelope correlation coefficient (ECC), isolation, multiple-input-multiple-output (MIMO), mutual coupling reduction, parasitic decoupling technique.

In this article, a pair of unsymmetrical dual‐feed antennas with one shared radiator and two isolated ports is proposed for multiple‐input‐multiple‐output (MIMO) systems. The proposed antenna pair achieves high isolation between the two ports by properly adjusting the distance between the two feeding ports and the position and length of shorting strips on the radiator. The antenna has simple structure and covers the 3.3‐3.7 GHz band, which could meet the demand of future 5G applications. The measured results show that antenna has good impedance matching (better than 10 dB return loss) and high port isolation (better than 20 dB isolation) from 3.35 to 3.65 GHz. The total efficiencies are above 55% and the envelope correlation coefficient is <0.1, which is sufficient for MIMO applications.

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