Decoupling of MIMO antenna array based on half-mode substrate integrated waveguide with neutralization lines

This paper proposes a miniaturized multiple-input and multiple-output (MIMO) antenna array based on half-mode substrate integrated waveguide (HMSIW). Initially, quarter-mode on the conventional HMSIW is introduced to widen the operating bandwidth while enabling the antenna to remain miniaturized. Then, the quasi-electric wall characteristics of metal via are adopted to orthogonally arrange four antenna elements without a gap to reduce the array size further. Next, the decoupling structure of composite neutralization lines (NLs) is used to improve the isolation of the MIMO antenna array. Each NL comprises a simple metal strip attached to each of the two antenna radiators to create an extra coupling path that opposes the primitive antenna coupling to reduce mutual coupling. Eventually, the 2 × 2 MIMO antenna array is fabricated and implemented to verify the design. The simulated and measured results are in good agreement. The measured impedance bandwidth of S11 less than −10 dB ranges from 5.05 to 5.43 GHz, and the peak gain of the element is 7.93 dBi on the broadside at the center frequency of 5.35 GHz, and the array gain reaches 10.09dBi. The mutual coupling levels between the orthogonal and the parallel antenna elements are −19.2, −19.1, and −15.9 dB, respectively. The overall size of the antenna array is only 1.06λ0 × 1.06λ0 × 0.025λ0, making it a suitable candidate for fifth-generation MIMO systems.