342 BELL SYSTEM TECHNICAL JOURNAL 



In Fig. 6.5-6(b) the proportions of the guide have been altered some- 

 what, but since the Unes of electric force are still perpendicular to the top 

 and bottom plates, the guide may be expected to function substantially 

 as before. At the most, some attenuation that previously originated in 

 the left-hand side wall may now be transferred to the top and bottom 

 walls. As a second step, we may extend the width of the top and bot- 

 tom walls as shown in Fig. 6.5-6(c) until they intersect, thereby forming 

 an arc-shaped guide. The attenuation now prevailing is evidently confined 

 to the top and bottom walls and the right-hand wall. It is reasonable to 

 assume that the side wall attenuation still decreases with frequency 

 since incident lines of force are everywhere parallel to this wall. As 

 a third step, we assemble as in Fig. 6.5-6(d) a number of identical arc- 

 shaped guides to form a composite circular guide with radial partitions. 

 If, finally, we imagine the radial partitions removed as in Fig. 6.5-6(e), the 

 resulting configuration will not be altered and we shall have removed the 

 component of attenuation attributable to the top and bottom walls leaving 

 only the component of attenuation attributable to the one side wall, which, 

 as we have pointed out, becomes progressively smaller as the frequency is 

 injefinitely increased. 



