708 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1954 



guide on a single coupling element basis, appears in modes other than 

 TEoi . Thus, the total coupling to TEio° is greater than to TEoi^. The 

 total coupling modifies the phase constant of each line, per (20'), and 

 since the total coupling coefficient is unequal for the TEio'-' and the 

 TEoi° modes, the perturbed phase constants should be expected to be 

 unequal when the unperturbed phase constants are made equal. A method 

 of determining the magnitude of this phase-constant disturbance has 

 been suggested by S. A. Schelkunoff. In this method the reflected wave 

 from a single coupling orifice is measured in the dominant waveguide and 

 in the single mode of interest in the multi-mode waveguide. Having de- 

 fined the ratio of the incident to the reflected power in the same mode by 

 the sympol p, Schelkunoff determines that the disturbed phase constant 

 i8', is related to the undisturbed phase constant jS by the relation 



/3 = ^ + 



(41) 



in which "d" is the distance between the coupling orifices in the coupling 

 arrangement which one wishes to evaluate. This relation may be used to 

 evaluate the change in the phase constant for the circular electric mode 

 and for the wave in the dominant waveguide, and the change of wave- 



tr 6 



UJ 



10 



20 



100 



200 



40 70 



NUMBER OF COUPLING HOLES 

 Fig. 45 — Transfer loss for the transducer of Fig. 42 after increasing the cou- 

 pling hole sizes and correcting the phase constant. 



