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BELL SYSTEM TECHNICAL JOURNAL 



for these three types, wave guides are somewhat similar in their 

 behavior to ordinary conductors when operated at the highest fre- 

 quencies but they depart radically at frequencies near cut-off. 



Calculations indicate that the i/o type of wave has a descend- 

 ing attenuation characteristic at all frequencies above cut-off. This 

 suggests that we may be able to realize very low attenuation merely 



5000 10,000 50,000 



FREQUENCY IN MEGACYCLES PER SECOND 



F"ig. 7 — Attenuations suffered by each of the more common types of waves in a 

 hollow copper pipe 5 inches in diameter. 



by raising frequency. This remarkable property is, so far as the author 

 is aware, altogether unique in the realm of electrical transmission. It 

 should be borne in mind, however, that for structures having reasonable 

 dimensions, these low attenuations can only be obtained from fre- 

 quencies that are above those now readily available. It may be noted 

 in passing that at the minimum of the //i curve, transmission is flat 

 to a half db per mile over a band-width of 4000 mc. 



