Design and performance investigation of an ultra-thin and flexible polyimide-based UWB Antenna

This paper presents the design and performance evaluation of a flexible ultra-wideband (UWB) 4-port MIMO antenna optimized for medical diagnostics and wireless health monitoring. The antenna is fabricated on a lightweight polyimide substrate ensuring flexibility, conformability and stable operation in wearable applications. It operates across a wide frequency range from 2.7 GHz to 10.5 GHz achieving an average measured gain of 4.01 dB and an efficiency of 76.2% when positioned 7 mm above the skin. The proposed X-shaped structure integrated with electromagnetic band gap (EBG) elements and slot resonators enhances impedance matching, mitigates surface wave losses and improves isolation between MIMO ports. Measured return loss confirms excellent impedance characteristics while isolation results indicate minimal mutual coupling. Radiation pattern analysis reveals stable directional characteristics making the antenna well-suited for biomedical applications. When placed directly on the skin, the average gain decreases to 1.19 dB and efficiency reduces to 50.13%—a degradation of 70.3% and 34.2% respectively which occurred primarily due to dielectric losses and absorption. Despite these variations, the antenna retains sufficient efficiency and isolation to support non-invasive medical diagnostics and wireless health monitoring.