A Compact $4\times 4$ 5G MIMO Array with Frequency Reconfigurable and Isolation Character

A novel frequency reconfigurable multiple-input multiple-output (MIMO) array with high isolation is presented in this paper. Controlling the content of the filling liquid in the container can alter the equivalent dielectric constant. The frequency reconfigurable range of 3.70 GHz to 2.80 GHz (a frequency tuning range of 27.7%) is realized by adjusting the fill rate $P$ of the liquid material from 0.13 to 0.95. With a decoupling neutralization line, the isolation in the operating band is increased to more than 15 dB. The proposed scheme provides a good choice for future MIMO communication that responds to multiple frequency bands.