5-6 MM ATTENUATION FOR THE CIRCULAR ELECTRIC WAVE 1123 



of oxygen in the waveguide in terms of (1) is plotted in Fig. 6. It will 

 be noted that this loss becomes very appreciable at the short wave- 

 length end of the band. At X = 5.2 mm this loss is in the 0.3-0.4 db/100 

 ft range. For the larger size waveguide hue (J^" I.D.) the loss due to 

 O2 is approximately equal to the theoretical wall losses; for the smaller 

 size lines this amounts to about a tenth the wall loss. At the other end 

 of the millimeter band the O2 losses are very small, being in the 0.02 

 - 0.03 db/100 ft range at X = 5.7 mm. 



The relative effects of theoretical wall and expected oxygen ab- 

 sorption losses are shown plotted in Fig. 7. For the two sizes of wave- 

 guide the upper dashed curve represents the combined effect of these 

 two factors and the lower solid line curve is the theoretical attenuation 

 of the TEoi mode in empty pipe. The shaded area indicates the increase 

 which is the result of oxygen absorption. 



In order to minimize the transmission losses in any practical system 

 it becomes desirable to exclude the presence of oxygen from the hne, for 

 example, by introducing an atmosphere of dry nitrogen. Since the ex- 



5.0 



4.5 



I- 



UJ 

 ID 



O 



o 



a. 

 Ill 



Q. 

 HI 



m 

 o 



UJ 



o 



4.0 



3.5 



3.0 



5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 



WAVELENGTH IN MILLIMETERS 



(a) TEq, loss IN 7/16" I.D COPPER 



0.8 



Z 

 O 



w 



z 

 < 



a. 



0.7 



0.6 



0.5 



0.4 



0.3 



0.2 



THEORETICAL WAVEGUIDE LOSS 



5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 



WAVELENGTH IN MILLIMETERS 



(.b) TEq, loss in ys" I.D. COPPER 



Fig. 7 — TEoi transmission losses. 



