Goubau management
A Goubau line , often also a Harms-Goubau line (also Goubot line or G line ), is a single-wire waveguide for technically used frequencies. This line is low loss but is rarely used, e.g. B. for supplying remote reception areas with VHF radio and television. The cable is named after Georg Goubau , who developed it in 1950 after Friedrich Harms had already described it theoretically in 1907.
It is an overhead line , needs a large distance to metallic and (especially lossy) dielectric parts and must not be bent if possible in order to keep radiation low.
Basic structure
A coaxial cable is reduced to the inner conductor. The wire is surrounded by a layer of dielectric , which reduces the propagation speed of the wave in the immediate vicinity of the conductor. This creates a Poynting vector that is slightly directed towards the conductor and guides the wave closer along the conductor than an uninsulated single-wire waveguide. The reduction in losses compared to a coaxial cable arises because a large part of the electrical field of the shaft lies outside the lossy dielectric.
To feed and terminate the line, exponential funnels are used, which produce the gradual transition of the characteristic impedance from the coaxial cable to that of the single-wire line. The funnels can also be manufactured in a material- saving skeleton construction. The distance between the individual segments must be less than half a wavelength. The widening of the funnel must be greater than half the wavelength.
Due to these specifications, the construction is only suitable for higher frequencies from around 50 MHz and up. Below this, the constructions are no longer practicable because of the resulting dimensions of the funnel and the required height above ground.
literature
- Friedrich Harms: Electromagnetic waves on a wire with an insulating cylindrical cover. Ann. Phys. 23, 1907, pp. 44-60.
- Alois Krischke: Rothammels Antennenbuch. 11th edition, Franckh-Kosmos-Verlags-GmbH, Stuttgart 1995, ISBN 3-440-07018-2
- Otto Zinke , Heinrich Brunswig: High Frequency Technology 1 . Springer, 1999, ISBN 978-3-540-66405-5 ( limited preview in Google book search).
Web links
- Table of contents of the Annalen der Physik , Volume 23, 1907. PDF; 0.4 MB Accessed: March 27, 2015