This work introduces a compact and novel MIMO antenna system with close spacing and exceptional isolation, tailored for broadband usage across frequencies from 3.7 to 11 GHz. The antenna configuration consists of two octagonal radiators, each individually powered by a 50 Ω microstrip line. The use of a modified ground structure ensures a wideband frequency range. A key novelty of this design is the incorporation of a strategically placed stub (25.6875 × 0.5 mm²) between the radiating sections, which significantly enhances inter-port isolation, achieving over 15 dB despite the minimal 3 mm port separation—an improvement over conventional MIMO antennas. This design enables high isolation without increasing antenna size, making it highly efficient for compact wireless systems. Performance evaluation, including fabrication and testing, demonstrates a strong alignment between simulation and experimental data. Metrics such as envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL) were analyzed to assess MIMO efficiency. The proposed antenna is ideal for broadband wireless systems with a peak gain of 6.5 dBi and excellent resonance, offering superior isolation and compactness compared to existing designs.

For forthcoming wireless applications, a small and highly decoupled complementary split ring resonators (CSRR)–loaded co-planar waveguide (CPW)–fed antenna for dual-band applications is investigated. The low-profile antenna consists of a CSRR-loaded rectangular radiating element with a truncated bottom, giving a wideband performance over the frequency ranges of 5.28–5.52 GHz and 6–7.2 GHz. The antenna has been printed on a widely used FR4 substrate measuring 7.5 × 10.5 × 1.6 mm³ in volume. This research’s suggested antenna is turned into a 4 × 4 multi input multi output (MIMO) construction using a 25 × 25 mm² printed circuit board. Individual antennas were isolated by nearly 20 dB without using a decoupling device. The antenna has been built, and the measured and simulated results correspond well. Computing envelope correlation coefficient (ECC), channel capacity (CC), and channel capacity loss (CCL) further validates the antenna’s performance (−). The antenna has an overall gain of around 2.54 dBi and a radiation efficiency of approximately 89% throughout the relevant spectral range, which is much better for wireless applications. The suggested antenna’s omnidirectional emission pattern makes it a potential contender for future wireless and cellular applications.

This study explores a novel approach to mitigate the challenge of a small ground plane inducing substantial back lobes in high front-to-back ratio (FBR) microstrip patch antennas. Introducing a combined technique employing rectangular strip and connecting strip methods, this research aims to counteract backward radiation by generating supplementary magnetic currents through an inductive effect. The hybrid method effectively reduces the backward radiation from the original patch. The proposed single antenna element occupies a notably smaller area (approximately 0.029 λ × 0.036 λ, where λ denotes the cutoff wavelength at 5.9 GHz), making it particularly suitable for wearable applications. Additionally, an equivalent circuit model illustrates the coordinated action, offering comprehensive insights into the physical mechanisms. The achieved FBR surpasses directivity by up to 6.03 dB, leading to a diminished specific absorption rate (SAR) when worn while maintaining minimal impact on radiation efficiency due to human presence, a crucial quality for wearable devices.

This research presents a novel four-port metamaterial-backed Multiple Input Multiple Output (MIMO) antenna system designed for X-band applications. Each modified circular-shaped antenna element is meticulously printed on a 1.6 mm thick FR4 substrate, resonating within the 9.2 to 9.9 GHz frequency range, encompassing a significant portion of the X-band spectrum. To enhance overall gain, a tilted square-shaped 4 × 4-unit cell is strategically printed on the ground plane of the substrate. The proposed MIMO antenna achieves a maximum gain of up to 8 dBi across the operating spectrum, coupled with an impressive radiation efficiency of up to 80%. Fabrication of the designed antenna is performed, and comprehensive parameter measurements validate its performance, exhibiting a close correlation with simulated results. Essential MIMO parameters such as ECC (10 dB), CCL (<0.3), and diversity gain are calculated to affirm the antenna’s proficiency further. The results show that the proposed antenna could be a suitable contender for X-band applications.