Also "G-line." It is a single wire transmission line intended for use at UHF and microwave wavelengths. The line itself consists of a single conductor coated with dielectric material. Coupling to and from the G-line is done with conical metal "launchers" or "catchers," with their narrow ends connected for example to the shield of coaxial feed line, and with the transmission line passing through a hole in the conical tips.

G-lines behave more as waveguides than as circuitry. Bends of large radius are tolerated, but too sharp a bend in the single wire will cause the line to radiate and lose energy into space. In theory the dielectric coating is a requirement, it slows the wave and focuses it along the wire. But some users note that in practice the finite conductivity of metals may produce a similar effect, and a bare G-line can entrain a propagating wave.

• Geog Goubau, "Surface waves and their Application to Transmission Lines," Journal of Applied Physics, Volume 21, Nov. (1950)