Performance evaluation and validation of a quad-element super-wideband fractal MIMO antenna with integrated quad-band filtering capability for advanced 5G/IoT systems

This research focuses on the design, simulation, and experimental validation of a four-port, fractal-loaded multiple-input multiple-output (MIMO) antenna to facilitate super-wideband (SWB) operation while suppressing undesired narrowband interference. The array design is prototyped on a cost-effective, 0.464λo × 0.285λo × 0.013λo (at 2.4 GHz) FR4 sheet. The top FR4 layer comprises four metallic hexagonal patches defected with a windmill-inspired rhombus fractal (2nd -order) pattern. At the same time, its rear side features a shared, multi-slotted ground combined with a hexagonal isolator. The designed array effectively transforms the fractal-induced multi-band into a 2.4–25 GHz SWB spectrum (164.96% fractional bandwidth) and significantly attenuates the cross-coupling between the array elements. The designed fractal minimizes the metallic radiator area by 48% compared to the conventional patch with a hexagonal configuration. Moreover, to ensure distortion-free communication, various undesired narrow bands, including downlink/uplink C-band (3.663–4.19 GHz/5.843–6.663 GHz), INSAT (4.48–4.87 GHz), and radio-location (8.969–10.51 GHz), are notched by integrating each array unit with two L-type slits, a rectangular split ring resonator (SRR) pair, and a modified complementary SRR. To assess performance in complex scenarios, the diversity measures are evaluated and observed to conform to their specified thresholds, thereby affirming the conformity between simulated and tested outcomes. Therefore, the designed SWB array facilitates the intrinsic interference immunity for seamless 5G/IoT communication in highly dense propagation environments.