Surface roughness and attenuation of precision-drawn, chemically polished, electropolished, electroplated and electroformed waveguides

Detailed examinations of certain 3cm waveguides have shown that the surface finish of precision-drawn tubing as manufactured at present is quite adequate for most applications. Such surfaces, however, may be improved, if desired, by careful chemical or electrolytic polishing or electroplating in bright baths under closely controlled conditions. Some information on the surface finish of copper guides electroformed on various types of mandrel is also presented. Formulae for calculating the attenuation of any H or E mode in a rectangular waveguide, so as to take account of surface roughness, have been developed from the original expressions derived by Kuhn. A method is given for determining the actual value of attenuation in a waveguide sample without having to make careful measurements with elaborate equipment on long specimens. A description is included of a new and simple technique, involving electropolishing, for examining the internal surface finish of waveguides; the method cannot, however, be used successfully on silver-plated sections.