This paper presents the design and comprehensive performance evaluation of a novel high-gain Terahertz (THz) Multiple-Input Multiple-Output (MIMO) antenna array. The proposed design incorporates a unique star-like and crescent-shaped radiating element integrated with both a Metasurface (MS) and a Parasitic Decoupling Structure (PDS) to achieve enhanced gain, high efficiency, and excellent inter-element isolation. Fabricated on a flexible polyimide substrate with a thickness of 10 µm, the antenna system leverages the substrate's low dielectric losses (tanδ = 0.0027) and relative permittivity ( \({\varepsilon }_{r}\) = 3.5) for optimal THz operation. An iterative design methodology is employed, progressively refining the single antenna element to achieve superior impedance matching, evidenced by an exceptionally low S11 of approximately − 39 dB at 0.68 THz. The integration of a 7 × 7 MS sheet is shown to significantly boost gain (up to ~ 7 dBi) and efficiency (over 90%) by reshaping the radiation pattern. Furthermore, the 4-element MIMO array, augmented with a central PDS, demonstrates outstanding decoupling characteristics, with mutual coupling coefficients (Sij) consistently below − 65 dB. The array achieves a peak gain of approximately 10 dBi and an efficiency exceeding 90% in the "MIMO with MS and PDS" configuration. Critically, the Envelope Correlation Coefficient (ECC) remains exceptionally low (below 0.005), and the Diversity Gain (DG) approaches 10 dB across the operating bandwidth, validating the array's robustness for high-data-rate and reliable THz communication. The compact size, flexible nature, and superior electromagnetic performance of this antenna array make it a promising candidate for next-generation THz wireless communication systems, including wearable electronics and biomedical devices.
