Goubau line
Template:Short description A Goubau line or Sommerfeld–Goubau line,<ref name="Yeh">Template:Cite book</ref> or G-line for short, is a single-wire transmission line used to conduct radio waves at UHF and microwave frequencies.<ref name="Straw" /><ref name="Lieberman">Template:Cite journal</ref><ref name="Griffith">Template:Cite book</ref> The dielectric coated transmission line was invented by F. Harms<ref name="Harms">Template:Cite journal cited in Stulle, Bergoz 2012 The Goubau line, p.148 Template:Webarchive</ref> in 1907 and George J. E. Goubau<ref name="Goubau">Template:Cite journal cited in Stulle, Bergoz 2012 The Goubau line, p.148 Template:Webarchive</ref> in 1950, based on work on surface waves on wires from 1899 by Arnold Sommerfeld.<ref name="Sommerfeld">Template:Cite journal cited in Stulle, Bergoz 2012 The Goubau line, p.148 Template:Webarchive</ref><ref name="Stulle">Template:Cite book</ref> It is used as a feedline at UHF to link high frequency transmitters and receivers to their antennas,<ref name="Straw" /><ref name="Lieberman" /> and in scientific research.<ref name="Stulle" />
DescriptionEdit
The Goubau line itself consists of a single wire conductor coated with dielectric material.<ref name="Straw">Template:Cite book</ref> 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.<ref name="Straw" /> An advantage of the Goubau line is that it can have lower attenuation due to dielectric losses at high frequencies than other types of transmission line. Parallel line (twin lead) and coaxial cable, which are used to carry lower frequency radio signals, have high losses at the upper end of the UHF band, and are almost useless for distances over 100 feet (33 meters).<ref name="Straw" /> Goubau lines can serve as low loss antenna feedlines at these frequencies, up to microwave frequencies where a waveguide must be used."<ref name="Straw" />
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.
Other structures besides horns have been used to couple radio waves into and out of Goubau lines; waves can be "launched" from planar structures like tapered coplanar waveguides at much higher frequencies, into the terahertz band. The dimension of the single metallic conductor is then typically 1 μm. <ref> T. Akalin, “High Resolution Biosensor based on Surface Wave Transmission Lines at THz Frequencies”, 35th European Microwave Conf., 3-7 Oct. 2005, Paris, France and
T. Akalin, "Single-wire transmission lines at terahertz frequencies", IEEE Transactions on Microwave Theory and Techniques (IEEE-MTT), Volume 54, Issue 6, June 2006 Page(s): 2762 - 2767 </ref>
The Goubau line conducts energy via one-dimensional electromagnetic surface waves, analogous to the two-dimensional surface waves called ground waves that carry the signal from MF AM broadcasting stations to home AM radios. The ability of surface waves to bend and follow the contour of a conductor explains why AM radio stations can be received on the far side of hills, and how over-the-horizon radar works.
See alsoEdit
PatentsEdit
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|{{US patent|123456|link text}}}}, "Surface wave transmission line". George J. E. Goubau
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