Design of an Eight-Element Double-Loop MIMO Antenna With Inverted-L Isolators

For the first time, an eight-element MIMO antenna is designed by integrating four double-loop resonators with two pairs of inverted-L isolators. By superimposing the resonance modes of the double-loop antenna, the antiphase currents of the loops can effectively be canceled out to achieve high isolation ($S_{12}$), without requiring additional decoupling elements or lumped components. The isolators have successfully generated a null point near the operating frequency for further enhancing the isolation ($S_{32}$) between the double-loop antennas. As a result, the proposed antenna can achieve good isolation levels of $S_{12}$ <−21.3 dB and $S_{32}$ <−29.5 dB across a 10 dB bandwidth in the N78 band (3.3 GHz to 3.8 GHz), and each port provides over 78% of total efficiency and ECC below 0.01 in experiments.