Embeddable Structure for Reducing Mutual Coupling in Massive MIMO Antennas

An embeddable decoupling structure is proposed for massive multiple-input-multiple-output (M-MIMO) antennas in this paper. The embeddable decoupling structure is made up of an end-folded metal strip and a pair of C-shaped metal strips. By introducing the embeddable decoupling structure near two closely spaced dipole antennas, additional coupling can be generated to counterbalance the original mutual coupling between the dipole antennas. The decoupling structure is firstly designed for a 1×2 MIMO antenna, which can provide a reduction of about 5 dB for the mutual coupling. Then, an evolutional decoupling structure is designed, which is composed of a pair of inverted U-shaped metal strips and two parallel reversed C-shaped metal strips. The evolutional decoupling structure is employed in a 3 × 3 MIMO antenna operating in 5G bands to demonstrate its capability of decoupling. An average reduction of about 10 dB on mutual coupling is obtained over 3.3-4.5 GHz (30.8%). Moreover, it is found that the deteriorated radiation patterns due to the mutual coupling are improved. The decoupling structure can be totally embedded in a M-MIMO antenna, which has no increase in the antenna volume. The proposed decoupling structure exhibits advantages of radiation pattern distortion alleviation, wideband, embeddable, and dual-polarized capabilities for M-MIMO applications.