DIELECTRIC-COATED WAVEGUIDE 



1267 



-100 

 -80 



-60 

 -50 



10 



_i 



eg 

 o 



Q 



UJ 



> 



LU 



UJ 



Q 

 O 



in 



D 



o 

 ir 



Q. 

 10 



-40 



-30 



-20- 



•10 



-5 



-4 



-3 



-1 



10 



20 30 40 50 60 80 100 200 



BEND RADIUS IN FEET 



300 400 600 



1000 



Fig. 5 — Spurious mode level in a uniform bend of a dielectric-coated guide. 

 2a = 2 inches; e = 2.5; X = 5.4 mm. 



in the normal mode. The bending radius R is a function of position and an 

 average bending radius, 



1 



R 



Av 



= -7 



z Jo 



' dz 

 R^ 



(29) 



has to be used in (20). 



All the attenuation terms (20) decrease with increasing coat thickness 

 5; the TEoi attenuation in the straight guide (10) and (14) increases with 

 6. Consequently there is an optimum thickness for which the total in- 

 crease in attenuation is a minimum. This optimum thickness depends on 

 the average radius of curvature. In Fig. 7 optimum thickness and the 

 corresponding increase in attenuation have been plotted versus the 

 average radius of curvature. 



In gentle curvatures the normal mode is a mixture of TEoi and TMn 

 only and the attenuation increase as caused by the curvature is given 

 by (27). In this case the optimum thickness and the corresponding 

 attenuation increase are: 



