A Coplanar Vivaldi-Style Launcher for Goubau Single-Wire Transmission Lines

In this letter, we present a coplanar Vivaldi-style launcher for single-wire transmission lines (SWTLs), sometimes called Goubau lines. The launcher converts a transverse electromagnetic mode (TEM) mode from a coaxial feed port to the transverse magnetic (TM01) surface-wave mode supported by the SWTL. The original Goubau design for SWTL launchers uses large horns to enforce the mode conversion. In contrast, the proposed coplanar Vivaldi-type launcher comprises a planar structure with dimensions of 100 mm x 150 mm, which is more convenient to install on existing infrastructure, such as power lines, communication wires, structural steel cables, or pipes. The proposed launcher can be used to provide a broadband communication channel for ultrahigh frequency and microwave radio-frequency signals from 0.81 to 2.29 GHz. It has a measured 10 dB return loss bandwidth of 1.39 GHz. The measured line loss with an 8 mm diameter SWTL conductor is approximately 0.19 dB/m at 1.5 GHz, which is comparable to high-quality coaxial cables. We have also shown that multiple launcher pairs can be used back-to-back on the same SWTL conductor to provide isolated communication links. With a launcher separation distance of 250 mm, the measured back-to-back isolation exceeds 30 dB.