892 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



0.6 



0.5 





0.4 



^f 



0.3 



0.2 



0.1 



I 



5800 5900 6000 6100 6200 6300 6400 



FREQUENCY IN MEGACYCLES PER SECOND 



6500 



Fig. 15 — Relative attenuation — forward direction 



rates of variation, a simple adjustment of parameters may be made to 

 cause the forward null and maximum reverse attentuation to appear 

 at the same frequency, resulting in an optimum performance. 



The occurrence of the reverse maximum loss in the region of X = Xj 

 may roughly be explained as follows. As the transverse air wave number 

 decreases, the admittance of the guide, defined on a power flow basis, 

 increases. The electric field magnitude distribution must therefore gener- 

 ally decrease in such a fashion as to cause the overall power flow to re- 



5600 5900 6000 6100 6200 6300 6400 



FREQUENCY IN MEGACYCLES PER SECOND 



6500 



Fig. 16 — Relative attenuation — backward direction 



