WAVEGUIDK AS A ("OMMnNICATlOX MllDMM 



1217 



where/ is the carrier frequency (cps), v is tlie ratio of the waveguide 

 cutoff frequency to tlie carrier friMpiencv, and L is Ihc Hue Iciijith in 

 miles. 



From the abo\'e relation, the inaximinn hasehaiid widtii aNailahlc has 

 been calculated for one mile of line as a function of carrier fi-ecjuency 

 with the loss held constant at 2 db per mile and 18.2 db ])er mile, and the 

 results are plotted in Fij;-. (1. The conditions for tlu'sc cui-\'es are directly 

 comparable to those for which Figs. 3 and 4 were calculated. At a carrier 

 freciuency near 50,000 mc, the circular electric wave in 2-inch diameter 

 pipe makes available a baseband width on the order of 500 mc for one 

 mile of line, or 100 mc for 25 miles of line. At lower frecjuencies, with the 

 wa\'eguide enlarged to hold the loss constant, there is less bandwidth 

 available. 



The 13.2 db per mile condition (in a smaller diameter of waveguide) 

 ])ermits the use of approximately one-half the bandwidth available at 

 the 2 db per mile condition. 



The above design considerations are the liasis for concluding that the 

 most attractive communication possibility is the use of carrier fre- 

 quencies on the order of 50,000 megacycles and associated waveguides 



^o 



Q 0.4 



5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 



NORMALIZED FREQUENCY (CUTOFF FREQUENCY = I.O) 



Fig. 5 — Normalized group velocity versus normalized freciueiicy for hollow 

 metallic waveguides. 



