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BELL SYSTEM TECHNICAL JOURNAL 



In a long wave guide the "i" mode will die down due to its greater attenua- 

 tion, no matter how much of it was initially present, so that one need only 

 consider the "a" mode. 



This mode has a phase velocity slightly smaller than that of the uncoupled 

 TEoi wave and an attenuation nearer to that of the TEoi than the TMn 

 wave. 



The magnitude of the critical radius is illustrated by the two examples 

 of Table I. 



Table I 

 Characteristic Values 



Table II 

 Relative Attenuation Versus Radius of Curvature 



The increase of attenuation in long wave guides with uniform curvature 

 is shown on Table II, with numerical values for the same examples as in 

 Table I. 



6. Propagation in a Uniformly Curved Section of Wave Guide 

 Following a Long Straight Section. (Fig. 4) 



No matter what mixture of modes may prevail at the beginning of the 

 wave guide, all modes except the TEoi die down in the long straight section 

 due to their higher attenuation, so that the wave form at the beginning 

 of the curved section is pure TEoi . 



Since it has been shown in Sections 1 and 4 that each of the two possible 



