WAVEGUIDE AS A COMMUNICATION MEDIUM 



1215 



10- 



4 5 6 S 



10' 



4 5 6 8 



10= 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 3 — Round guide diameter versus frequency for attenuation of 2 db/mile. 



As a consequence of the iiiiiisiial loss versus frequency characteristic 

 of the circular electric wave, the diameter required in order to achieve a 

 given loss decreases as the carrier frequency increases. This is illustrated 

 by the curves labeled TEoi in Figs. 3 and 4. All other waveguide modes 

 (except higher-order circular-electric waves, TEom) have a characteristic 

 of the general form sketched for the dominant wave (TEn) also shown 

 in Figs. 3 and 4. The longitudinal wall currents contribute a loss com- 

 ponent which rises at increasing frequencies due to skin effect; this ac- 

 counts for the positive slope of the TEn curve at the right-hand side of 

 Figs. 3 and 4. The negative slope of the TEoi curves and of the left-hand 

 portion of the TEn cur\'es in Figs. 3 and 4 is a consecjuence of losses 

 associated with the wall currents which prevent the wave from spread- 

 ing as it would in an unbounded medium; these currents and the losses 

 associated with them decrease as the operating fretjuency becomes 

 farther removed from cut-off'. 



For a loss of 2 db per mile Fig. 3 shows that a waveguide 1" in diam- 

 eter is recjuired in the freciuency band near 4,000 me where the TI)-2 

 system operates. Whereas this may not Ix' pr()hil)itive in a comiectiiig 



