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

Ultra-Thin and Flexible Polyimide-Based UWB Antenna • A novel ultra-thin and flexible 4-port UWB MIMO antenna is proposed for wearable biomedical diagnostics and wireless health monitoring. • The antenna is fabricated on a 0.1 mm polyimide substrate, offering high flexibility, light weight, and superior conformability to body curvature. • It operates effectively from 2.7 GHz to 10.5 GHz with average measured gain of 4.01 dB and efficiency of 76.2% at a 7 mm gap from the human body. • When placed directly on the skin, gain drops to 1.19 dB and efficiency to 50.13%, yet still supports diagnostic operation. • An X-shaped central structure integrated with EBG slots enhances mutual isolation and maintains impedance stability. • The antenna demonstrates stable radiation patterns and consistent gain across UWB frequencies despite body loading effects. • CPW-fed structure and ground slot optimization contribute to wideband performance and efficient MIMO decoupling. • Measured return loss remains below –10 dB across UWB range, ensuring efficient energy transfer. • Isolation remains better than –20 dB across all ports due to the orthogonal X-shaped decoupling and embedded EBG units. • Surface current and diversity analysis confirm low ECC (<0.05) and high Diversity Gain (6–10 dB), critical for MIMO performance. • Comprehensive parametric studies validate the effect of spacing from skin and integration of EBG for gain and efficiency improvement. • Comparison with literature highlights superior gain, bandwidth, substrate flexibility, and MIMO support in biomedical scenarios. • Future work will include bending/crumpling simulations, SAR analysis, and extended mathematical modeling. 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.