A compact Coplanar Waveguide (CPW) super-wideband (SWB) two-port Multiple-Input Multiple-Output (MIMO) antenna is presented, featuring a hexagonal patch with a triangular slot embedded in an octagonally-slotted ground and fabricated on Rogers RO5880 ( \({\varepsilon }_{r}\) = 2.2, h = 0.8 mm, tanδ = 0.0009). The design provides continuous impedance coverage from 5.3 to 46.6 GHz (fractional bandwidth ≈ 159.15% \({f}_{H}/{f}_{L}\) ≈ 8.79:1, ≈ 3.14 octaves). The two-element MIMO layout (overall size 36 × 18 × 0.8 mm3, unit cell 18 × 18 mm2) uses 3.22 mm inter-element spacing to achieve spatial/polarization diversity and measured isolation better than − 20 dB. Simulated and measured results show good agreement with a measured peak gain of 5.8 dBi and a stable efficiency of 85% at the frequency of 5.3 GHz. Key MIMO performance metrics are excellent, including an envelope correlation coefficient less than 0.02, a diversity gain of approximately 9.98, a channel capacity loss below 0.4 bits per second per hertz, and a total active reflection coefficient lower than − 10 dB, confirming low correlation and strong diversity performance. The proposed antenna is therefore a promising candidate for ultra-wideband and super-wideband fifth and sixth-generation (5G/6G) mobile communication systems as well as millimeter-wave portable and multiband applications.
