A compact four-port multi-input, multi-output (MIMO) antenna with good isolation is proposed for sub-6 GHz and Internet of Things (IoT) applications. Four similar L-shaped antennae are placed orthogonally at 7.6 mm distance from the corner of the FR4 substrate. The wideband characteristics and the required frequency band are achieved through the L-shaped structure and with proper placement of the slots on the substrate. To obtain good isolation between the ports, rectangular slots are etched in the bottom layer and are interconnected. The proposed antenna has total dimensions of 40 mm × 40 mm × 1.6 mm. The interconnected ground plane provides good isolation of less than -17 dB between the ports, and the impedance bandwidth obtained by the proposed four-port antenna is about 54% between the frequency range of 3.2 GHz to 5.6 GHz, thus providing a wideband antenna characteristic covering sub-6 GHz 5G bands (from 3.4 to 3.6 GHz and 4.8 to 5 GHz) and the WLAN band (5.2 GHz). The proposed design antenna is fabricated and tested. Good experimental results are achieved when compared with the simulation results. As the proposed design is compact and low profile, this antenna could be a suitable candidate for 5G and IoT devices.
Microwave imaging (MWI) presents a promising, safer, more affordable, and portable alternative for detecting strokes compared to traditional methods, such as CT and MRI, which have limitations related to radiation exposure, cost, and accessibility. This paper focuses on the design and performance evaluation of a compact, T-shaped, two-port Multiple-Input Multiple-Output (MIMO) antenna, developed explicitly for microwave-based brain imaging. MWI operates by exploiting differences in tissue dielectric properties to identify and visualize abnormalities, with ultra-wideband (UWB) antennas configured in a two-port setup to improve signal penetration. The antenna, fabricated on an FR4 substrate with a dielectric constant (εr) of 4.3, effectively functions within the 3.1-6 GHz frequency range. It demonstrates a broad impedance bandwidth and maintains excellent isolation. Both simulated and measurement results confirm its reliable performance, showing consistent return-loss characteristics and stable omnidirectional radiation patterns. Furthermore, the antenna exhibits a very low envelope correlation coefficient (ECC 9.9 dB), and favorable mean effective gain and total active reflection coefficient (TARC) values. When integrated into a human head model, this MIMO antenna configuration has shown minimal mutual-coupling (below - 15 dB) and significant potential for non-invasively detecting hemorrhages by carefully monitoring changes in scattering parameters. This proposed system underscores the capability of compact MIMO antennas to enable portable, non-invasive, and rapid stroke diagnosis, offering particular advantages for patients who lack access to conventional imaging facilities.