Metasurface-Assisted mutual coupling suppression in circularly polarized MIMO antenna array for Sub-6 GHz applications

A double-sided decoupling metasurface (DSDM) method is proposed to reduce the mutual coupling between very closely spaced circularly polarized (CP) MIMO antenna elements for sub-6 GHz applications. A proposed DSDM structure with a square-shaped patch layer is placed over the array to reduce mutual coupling by non-propagating evanescent waves and manipulating the polarization of propagating reflected CP waves. This decoupling mechanism relies on the DSDM's negative electric permittivity extracted from the meta-atom. When the CP waves were incident to DSDM polarizer through the excited CP antenna of the array, the polarization states of the reflected and transmitted CP waves were changed as controlled by DSDM. In reflection mode, the negative permittivity of DSDM produce two type of the waves reflected waves generated the polarization mismatch and evanescent waves that reduce the coupling between CP antennas, while the transmission mode, controlling the radiation pattern at φ = 45° or φ = 135°. The low-profile proposed decoupling structure was fabricated and experimentally validated. The decoupling design significantly mitigated the measured mutual coupling between the CP antenna elements at 3.5 GHz by more than 15 dB and by more than 13 dB at 3.02 GHz to 3.67 GHz, compared to the reference array. The proposed design achieves less than a 3 dB axial ratio, maximum realized gain of 5.52 dBic at 3.5 GHz. An excellent agreement between the simulated and measured outcomes has been studied.