A Half-Mode SIW Cavity-Backed 3-Ports MIMO Antenna

In this article, a compact and low-profile rhombus-shaped antenna is designed and extended to a 3-element multiple-input multiple-output (MIMO) antenna with a defected ground structure (DGS). A reduction in the antenna footprint by 50% is achieved which implies a decrease in the physical area occupied by the antenna to half of its original size, hence Half-mode Substrate Integrated Waveguide (HMSIW) technology is utilized in the proposed antenna. A rectangular slot is etched at the center of the HMSIW cavity which enhances the overall bandwidth of the antenna by 50%. The slot at the center of the cavity splits the dominant TE110 mode of the HM cavity into odd- and even-half TE110 modes in proximity. The antenna resonates around 5.7 GHz and 5.8 GHz in proximity which covers a bandwidth of 200 MHz. The isolation levels between any two radiating elements are improved by a Y-shaped slot in the ground plane, obtained below -20 dB. The overall size of the three-port MIMO antenna is 1.0λgx 0.8λg. The peak gain of the antenna is obtained at 5.9 dBi at a lower resonant frequency and 6.25 dBi at an upper resonant frequency while radiation efficiency is better than 90% in a complete frequency band. The MIMO antenna performance metrics are evaluated theoretically and compared with the simulated results. The envelope correlation coefficient (ECC) is obtained less than 0.015, DG is around 9.9 dBi, and mean effective gain (MEG) is around -3.05 dB.