NORMAL MODE BENDS FOR CIRCULAR ELECTRIC WAVES 1307 



waveguide usually break down at smaller than optimum values of the 

 coat thickness. 



It should be mentioned finally that the normal mode bend is an in- 

 herently broad band device. Except for the oscillations of the mode con- 

 version portion of the total loss as caused by spurious mode phasing, 

 there is only a gradual change of the loss with frequency. 

 P Some terms contributing to the total loss decrease with frequency, 

 others increase. The over-all frequency dependence is of the same order 

 as the frequency dependence of the loss in the straight waveguide. As an 

 example, in Fig. 5 the bend loss has been plotted versus frequency for 

 the normal mode bend of Fig. 4. 



ACKNOWLEDGMENT 



Mathematical analysis of tapered curvature in other forms of wave- 

 guide has been made by others. S. E. Miller reports that Siemens & 

 Halske A. G., Germany, have made an original treatment of this sub- 

 ject. 



REFERENCES 



1. H. G. Unger, Circular Electric Wave Transmission in the Dielectric Coated 



Waveguide, pp. 1253-1278, this issue. 



2. S. E. Miller, Coupled Wave Theory and Waveguide Applications, B.S.T.J., 33, 



pp. 661-719, May, 1954. 



3. W. H. Louisell, Analysis of the Single Tapered Mode Coupler, B. S.T.J. , 34, 



pp. 853-870, July, 1955. 



4. R. W. Klopfenstein, A Transmission Line Taper of Improved Design, Proc. 



I.R.E., 44, pp. 31-35, January, 1956. 



5. S. P. Morgan, Theory of Curved Circular Waveguide Containing an Inhomo- 



geneous Dielectric, pp. 1209-1251, this issue. 



