A Four-Port MIMO Antenna Featuring Multi-Band Functionality With Improved Isolation for Terahertz Systems

The increasing saturation of microwave frequencies poses challenges for modern networks, making terahertz (THz) communication a promising solution for higher data rates, provided energy-efficient devices are developed. This study presents an innovative quad port multi-input multi-output (MIMO) antenna for sixth-generation (6G) terahertz wireless communications applications. The single-element radiator featuring a patch of modified elliptical quadrant shape in the presence of a C-shaped ground plane is conceptualized at an initial stage. Furthermore, two and four elements-based MIMO structures are constructed by placing the conceptualized single antenna elements. Additionally, the proposed configuration of the quad-element MIMO antenna comprises a plus-shaped isolation structure with a circular ring on a low-cost, transparent polyimide substrate. This innovative design enhances multi-resonance behavior, optimizes impedance matching, and achieves miniaturization while maintaining high isolation. The antenna operates across five distinct frequency bands: 0.97–1.27, 3.37–3.9, 8.68–9.17, 11.02–11.79, and 13.36–13.80 THz, with fractional bandwidths (FBW) of 26.79%, 14.59%, 5.49%, 6.75%, and 3.24%, respectively. It achieves a peak gain of 8.09 dBi and a radiation efficiency exceeding 82%. The antenna demonstrates exceptionally low mutual coupling (<30 dB) between adjacent elements along with attractive MIMO metrics, offering a low ECC of 0.0001, DG close to 10, a TARC of less than -10 dB, and a CCL of 0.4 bps/Hz. These results confirm the antenna's potential as an effective solution for THz MIMO systems, positioning it as a strong candidate for next-generation 6G wireless communications utilizing terahertz spectrum.