Isolation improvement between two tightly coupled QMSIW MIMO antenna elements using spoof surface plasmon polariton structure

A spoof surface plasmon polariton superstrate structure-based decoupling method is proposed in this paper to reduce mutual coupling between two tightly coupled quarter-mode substrate integrated waveguide antenna elements. This superstrate is a periodic structure suspended over the antenna elements with an inter-element spacing of 0.02 λ₀ (1 mm) at 6 GHz. It has been demonstrated that the isolation can be improved from 6.5 dB to more than 39 dB within the operation band in measurement. Further, it has been shown that the proposed method can improve both the total efficiency (by 25%) and gain (1.4 dBi) of the multiple-input multiple-output antenna.