A multi-band broad bandwidth inverted-C & F-shaped MIMO antenna for enhanced wireless connectivity

• A compact multiband 4 × 4 MIMO antenna is proposed, operating over 3.3–3.8 GHz, 12–18 GHz, and 24–38.2 GHz bands. • Utilizes inverted C- and F-shaped microstrip structures along with a defected ground structure (DGS) for enhanced bandwidth and isolation. • Achieves high isolation (< –25 dB), peak gain of 6.3 dBi at 13 GHz, and radiation efficiency >90 %. • Maintains a compact size of 0.3 × 0.3 λ² with integrated decoupling structure. • SAR remains within IEEE and ICNIRP safety limits, confirming suitability for mobile, Ku-band satellite, and mmWave applications. This research presents a multiband, broadband multi-input multi-output (MIMO) antenna designed for high-performance wireless communication systems. The proposed antenna operates over three extensive frequency bands: 3.3–3.8 GHz, 12–18 GHz, and 24–38.2 GHz. The antenna's primary structure comprises an inverted C-shaped microstrip radiator positioned above the feedline to facilitate resonance at 3.5 GHz. To enable additional resonances at 15 GHz and 31 GHz, an F-shaped microstrip extension is incorporated. A defected ground structure (DGS) is employed beneath the substrate to improve bandwidth and inter-element isolation. The configuration is extended from a single element to a 4 × 4 MIMO array by integrating a decoupling structure on the rear side of the substrate, resulting in a compact form factor of 0.3 × 0.3 λ². The proposed design achieves high isolation, with measured S-parameters showing values above –25 dB. Experimental validation confirms a peak gain of 6.3 dBi at 13 GHz and radiation efficiency exceeding 90 % across the operational bands. Moreover, the specific absorption rate (SAR) remains within the safety limits defined by international standards, ensuring suitability for practical deployment. Owing to its wideband performance, compact size, and high isolation, the proposed MIMO antenna is a promising candidate for applications in 5G mobile terminals, Ku-band satellite communications, and millimeter-wave (mmWave) wireless systems.