1214 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



were not present, but these currents decrease rapidly with increasing 

 frequency in a given waveguide size. Only in a straight circular pipe can 

 all of the electric field lines close upon themselves, and only in 

 the straight circular pipe does the attenuation approach zero at infinite 

 fretiuency.* 



Fig. 2 — Sketch of the magnetic intensity (//), electric intensity (E) and 

 Poynting Vector (P) for parallel-wire and circular-electric waveguides. Because 

 the main energy flow (P) in the circular electric waveguide is associated with 

 electric field lines that close on themselves and do not produce accumulations of 

 charge on the metal walls, the wall currents and associated losses are very small. 



* For further discussion, see G. C. Southworth, Principles and Applications of 

 Waveguide Transmission, D. Van Nostrand, Inc. pp. 175-178. 



