Stitched Transmission Line for Broadband Operations

Abstract

Wearable stitched transmission lines made from stripped RG174 and textile materials are introduced for broadband operations. The stitched transmission lines which are 150 mm long consists of an inner conductor surrounded by a tubular insulating layer. For shielding purposes, the structures are stitched into a denim material with conductive threads. The performances of the stitched transmission lines with three different stitch patterns, Double Overlock, Flatlock stitch and Ric-Rac stitch were investigated and results obtained confirm that Ric-Rac stitched transmission line has fewer DC losses than the three stitched transmission lines for frequencies up to 1 𝐺𝐻𝑧. However, beyond that up to 2.4 𝐺𝐻𝑧 and above, it was observed that the Flatlock stitched transmission line and the Double Overlock stitched transmission line have fewer radiation losses compared to the Ric-Rac stitched transmission line. Similarly, the performance of the stitched transmission line when bent through curved angles of 90° and 180° was considered, and a much better 𝑆ଶଵ was observed with a curved angle of 180° for frequencies below 2.1 𝐺𝐻𝑧, with radiation loss increasing afterwards. Finally, the sensitivity of the design to manufacturing tolerances, with changes in cross-sectional dimensions of the stitched transmission line and the transmission characteristics with different textile substrates were both considered. While simulated results showed that the stitched transmission line is sensitive to small variations in its circular dimensions, measured results conversely showed that Denim and Felt materials can be used as a substrate without any significant effect on its propagation characteristics.