HELIX WAVEGUIDE 



1377 



29.32 



29.28 



29.24 



29.20 



/3a 



29. 16 



29.1 2 



29.08 



29.04 



29.00 



0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40 0.44 



aa 



0.5 

 0.4 



0.2 



0.10 

 0.08 



0.06 

 0.04 



0.02 



1000 600 400 200 100 60 40 20 10 8 6 4 2 1 



e" 



Fig. 4 — Comparison of exact and approximate formula.s for the propagation 

 constant of a typical mode (TM02- limit in a guide with/3oa = 29.554 and «' = 4). 



staiit first becomes larger, in all cases, than predicted by the approximate 

 formula. For still lower conductivities the attenuation constant may pass 

 through a maximum, as in the present example, and decrease again. The 

 existence of a maximum in the attenuation vs conductivity curve is not 

 indicated by the approximate formula. 



