WAVEGUIDE AS A COMMTTXirATIOX MEDTT-M 



1255 



Fig. 28 — ^Nlode filters which pass only circuhir electric waves. 



they were in the sector at the left-hand end of Fig. 27, and the circular- 

 electric wave emerges in the round pipe. This type of transducer has 

 been shown to have transfer losses from dominant-mode rectangular 

 guide to circular-electric wave in round pipe of approximately 0.3 dh at 

 24,000 mc. Similar models have been made by A. G. Fox for use at 48,000 

 mc. 



Another important component is the mode filter previously referred to 

 and which attenuates all wave types other than the circular electric 

 wave family. One type of mode filter to perform this function is the 

 spaced ring structure of Fig. 26 and another type, due to A. P. King, 

 consists of resistive sheets along radial planes as shown in the photo- 

 graph of Fig. 28. The circular electric wave family has no electric field 

 in a radial direction or in a longitudinal direction. All other wave types, 

 however, have radial-electric or longitudinal-electric field components 

 and experience attenuation due to the presence of the resistive sheets. 



The coupled-wave type of transducer sketched in Fig. 29^ is useful in 

 connecting from dominant rectangular guides to the circular electric or 

 other modes in round guide. This type of transducer makes use of the 

 fact that the various modes in the multimode guide have unequal j^hase 

 constants. The transfer of power from rectangular guide to the round 

 guide takes place only to the particular round-guide mode whose phase 

 constant is equal to that of the wave in the rectangular guide. This type 



