1350 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



region where the approximate formulas for the propagation constants 

 of the lossy modes break down, some numerical results have been ob 

 tained for helices of zero pitch using an IBM 650 magnetic drum calcu 

 lator. Tables and curves are given showing the propagation constants of 

 various modes in such a waveguide, as functions of the electrical proper- 

 ties of the jacket and for three different ratios of radius/ wavelength. In 

 many cases it is found that the attenuation constant of a given mode 

 passes through a maximum as the jacket conductivity is varied, the 

 other parameters remaining fixed. The numerical calculations indicate 

 that it is possible to get unwanted mode attenuations several hundred 

 to several hundred thousand times greater than the TEoi attenuation 

 for the size Avaveguide that looks most promising for low-loss communi- 

 cation. 



US 



J," 



Fig. 1 — Schematic diagrams of the helical sheath and the helical sheath de- 

 veloped, showing the unit vectors and the periodicity. 



