5-6 MM ATTENUATION FOR THE CIRCULAR ELECTRIC WAVE 1127 



-e 



Fig. 10 — Mode filters. 



I 



ji relative to the average diameter and the rows marked B indicate the 

 corresponding variations in inches. The average ovahty gives the aver- 



, age difference between maximum and minimum diameters, maximum 



i ovahty the maximum difference in diameter and the maximum toler- 

 ance gives the maximum difference between diameter and ovality. 



' These measurements have been limited to measuring at the two ends 

 of each section of pipe. In spite of this small sampHng the TEoi loss 

 measurement appears to follow the I.D. tolerances quite well; the 

 OFHC line shows both the lowest attenuation and the best tolerances. 

 Mode interference effects can be reduced considerably by increasing 

 the loss to the undesired modes. This effect can be accomplished by modi- 

 fying the structure so that the spurious modes are highly attenuated 

 while the TEoi losses are increased only slightly. One way is to construct 



Table II — Average Performance of TEoi Waveguides with 



Mode Filters 



a measured (average db/100 ft.). 

 a measured 



a calculated 



Vie" I.D. OFHC 

 copper 



4.24 ± 0.1 

 1.16 



W l.p. low phos. 

 deoxidized copper 



0.51 ± 0.025 

 1.39 



%" I.D. copper 

 lined steel 



0.56 ± 0.012 

 1.52 



