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Goubou line

A Goubau line, Goubou line, or G-line for short, is a single wire transmission line intended for use at UHF and microwave wavelengths [1]. 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.

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A G-line is a type of waveguide, rather than a wire in an electric circuit. The G-line functions by slowing the propagation velocity of EM waves below the free-space velocity, causing the wavefronts to slightly bend inwards towards the conductor, which keeps the waves entrained. 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.

Note that the Goubau-Line are not exclusively coupled to 3 dimensionnal horn antennas, and can be used at other frequencies besides UHF and Microwave. Waves can be "launched" from planar structures like tapered Coplanar Waveguides (CPW) at much higher frequencies such as the Terahertz Band [2]. The dimension of the single metallic conductor is then typically 1µm.

Patents

U.S. Patent 2,685,068 , "Surface wave transmission line". George J. E. Goubau
U.S. Patent 2,921,277 , "Launching and receiving of surface waves". George J. E. Goubau.

References

Geog Goubau, "Surface waves and their Application to Transmission Lines," Journal of Applied Physics, Volume 21, Nov. (1950)
T. Akalin, A. Treizebré and B. Bocquet, “High Resolution Biosensor based on Surface Wave Transmission Lines at THz Frequencies”, 35th European Microwave Conf., 3-7 Oct. 2005, Paris, France

Category: Microwave technology