Isolation and Bandwidth Enhancement in Compact CP MIMO DRA in H-Plane Using Z-Shaped Strip

In this letter, we investigate the use of decoupling structure to improve isolation and bandwidth in a multiple-input–multiple-output (MIMO) dielectric resonator antenna (DRA). The MIMO antenna consists of two identical DRAs that are fed by the same rectangular slots to excite the fundamental mode (TE $_{111}$ ). In total, two annular vias are inserted in each DRA to realize circular polarization at this mode. Moreover, the annular vias create quasi-hybrid mode (HEM $_{11\delta }$ ) in the DRA. Vertical and Z-shaped strips are printed on the adjacent walls of DRAs for isolation purposes, in which the Z-shaped strips are coupled with the annular vias to realize the circular polarization at the HEM $_{11\delta }$ mode. Thus, improved bandwidth and isolation are achieved without occupying additional space. A prototype was fabricated and measured, which showed an overlapping 3 dB axial ratio bandwidth (ARBW) of 13.8% (2.7–3.1 GHz) with an isolation of 20 dB across the bandwidth, keeping the interelement spacing of 0.03 $\lambda _{0}$ . The measured radiation patterns were in agreement with simulated results in $\phi =0$ $^\circ (xz\text{-plane})$ and $\phi =90$ $^\circ (yz\text{-plane})$ planes, achieving a peak right-handed circularly polarized gain of 4.3 dBi for a single port.