Compact 2 W 2 MIMO Antenna with Low Mutual Coupling Based on Half Mode Substrate Integrated Waveguide

This communication proposes a novel compact multiple-input multiple-output (MIMO) antenna with low mutual coupling based on a $2 \times 2$ dual-polarized half-mode substrate integrated waveguide (HMSIW). The antenna is printed on a single-layer substrate to provide a low profile and ease of integration with planar circuits. The proposed HMSIW antenna element operates in TE110 mode and can be orthogonally arranged with two slots on the ground between the antenna elements, resulting in low mutual coupling. The edge-to-edge element space is only $0.033\lambda _{0}$ ( $\lambda _{0}$ is the free-space wavelength). A new miniaturized decoupling structure of neutralization lines is proposed to further reduce the mutual coupling by −10 dB in comparison with the ground slot structure. The $2 \times 2$ MIMO antenna was fabricated and implemented to verify the design. The simulated and measured results were in good agreement. The measured impedance bandwidth of $\vert \text {S}_{11} \vert $ less than −10 dB ranges from 5.025 to 5.135 GHz, and the peak gain is 5.6 dBi on the broadside at the center frequency of 5.08 GHz. The mutual coupling levels between the orthogonal and the parallel antenna elements are −45 and −36 dB, respectively. The envelope correlation coefficient is lower than 0.003 across the operating bandwidth. The overall size of the antenna is only $1.08\lambda _{0} \times 1.08\lambda _{0} \times 0.025\lambda _{0}$ , making the antenna a suitable candidate for upcoming fifth-generation MIMO systems.