Near-End and Far-End Coupling Investigations of Conductive Fiber Transmission Lines (TLs) on an Ultrathin Denim Substrate

An experimental validation is carried out in this research to investigate the potential uses of a conductive fabric as a Transmission Line (TL) for the feed networks of wearable antenna arrays utilized in biomedical wearable applications. Initially, a 50$\Omega$ conductive fabric microstrip transmission line with a 100 mm length was manufactured on a 0.7 mm denim substrate. The wave propagation properties of the prototype were measured and compared to the propagation properties of an ideal copper-based 50 $\Omega$ TL. The results showed that conductive fabric-based TL supports wave propagation properties similar to that of copper-based TL from 500 MHz – 10 GHz. However, conductive fabric-based TL experiences losses at higher frequencies due to lower conductivity and large surface roughness. Afterward, for the undesired mutual coupling investigations in the feed network, a parallel TL with a separation of 6.0 mm was then manufactured and tested. Overall, the near-end and far-end coupling investigations show that coupled conductive fabric-based TLs provide isolation in a manner similar to that of ideal copper-based TL. The results also show that conductive fabric-based TL is more immune to coupling at high frequencies thus useful for most demanding conformal applications.