Half-mode SIW cavity antenna for tri-band MIMO applications

A half-mode (HM) substrate-integrated-waveguide (SIW) cavity antenna is designed for tri-band multiple-input-multiple-output (MIMO) applications. Three cavity edges are shorted by metal posts while one aperture is open to radiate cavity energy into free space. To meet MIMO applications, a T-shaped slot is etched to split the single HM cavity into two equal SIW subcavities and then they are excited by coaxial feeding ports to realize two antenna elements. To obtain tri-band operations, four additional rectangle slots are cut, which introduces six quarter modes with different resonating regions. With the cavity size of 0.20 lambda(0) x 0.40 lambda(0), a fabricated prototype exhibits three operating bands with center frequencies of 3.33, 4.09, and 4.72 GHz and peak gain of 4.51, 4.05, and 3.93 dBi. Moreover, the measured port isolation is higher than 18.26 dB and the measured envelope correlation coefficient is below 0.05 within the frequency of interest.