1264 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 



Table V — Ratio of Attenuation Coefficients for Several 

 Modes in 4.732" Diameter. Waveguide at Xo = 3.0 Cm 



equal to 1.6 db/mile), and the ttxh/ciih ratios for the other modes range 

 from 2.5 to 100 times the TEoi value. Table V represents a selection of 

 the various modes which can exist in the 5-inch diameter line, but the 

 number tabulated is not an indication of the density of the ratio of at- 

 tenuation coefficients near a given value. Actually, there are eight modes 

 having ttxh/cLih ratios in the range 2.5 to 10, 19 modes in the range 10 to 

 20, and 15 modes greater than 20. 



Experimental work reported elsewhere shows that significant con- 

 version takes place between TEoi and the TEn , TE21 , TE31 and TMu 

 modes. There is some likelihood that conversion to TE12 takes place, 

 but the magnitude has not been measured. The experience gained by 

 measurement, therefore, shows that most typical conversions occur be- 

 tween TEoi and modes having attenuation ratios axh/am in the range 2.5 

 to 12. 



The absolute magnitudes of the conversion coefficients aix have in 

 some cases been measured directly, and may also be inferred from meas- 

 urements of total signal attenuation on the 500 ft. experimental line and 

 separate knowledge of the heat-loss values; the inference is that a^ must 

 fall in the range 0.1 to 1.0 au for the particular line studied. 



References 



1. S. E. Miller and A. C. Beck, Low-Loss Waveguide Transmission, Proc. I. R 



E., 41, pp. 348-358, March, 1953. 



2. S. E. Miller, Coupled-Wave Theory and Waveguide Applications, B. S. T. J., 



33, pp. 661-720, May, 1954. 



3. M. Aronoff, Radial Probe Measurements of Mode Conversion in Large Round 



Waveguide with TEoi Mode Excitation, presented orally at the March, 

 1951, I.R.E. National Convention. 



