COUPLKD WAVE THEORY AND WAVEGUIDE APPLIf'ATION'S 



709 



5W 



50 



30 



40 



50 



100 



110 



120 



Fig. 



60 70 80 90 



NUMBER OF COUPLING HOLES 



46 — Rectangular guide insertion loss for the transducer of Fig. 42. 



guide dimensions required to correct this phase constant difference may 

 be computed as though the coupling elements were not present. 



For the small phase constant disturbances which are associated with 

 the Aveak couplings employed, this procedure was found very accurate. 

 The reflection measurements and associated calculations for the model 

 of Fig. 42 indicated that the rectangular guide width should be 0.340" 

 for equality of phase constants instead of 0.359" as computed neglecting 

 coupling effects. The measured value of the transfer loss when the in- 

 dividual coupling holes had been enlarged and the rectangular guide 

 width had been altered to the 0.340" value is shown in Fig. 45. It is 

 evident that the theoretical value of db transfer loss was approached, 

 and that the shape of the transfer loss versus number of coupling ele- 

 ments, was reproduced very well. The 0.75 db minimum transfer loss 

 consisted of no more than 0.3 db heat loss, the remaining loss being due 

 to power present in other modes. 



The measured insertion loss in the rectangular waveguide is shown as 

 a function of the number of coupling holes at the three frequencies in 

 Fig. 46. Complete power transfer would, of course, correspond to an in- 

 finite insertion loss in the rectangular waveguide. It is interesting to note 

 that at 24,000 mc the peak in the rectangular guide insertion loss occurred 

 at 85 coupling elements whereas the maximum in the TEio'-' — TEoi° 

 transfer loss characteristic occurred at about 96 couphng elements (Fig. 

 45). This difference is likely to be the result of power transferred back 

 to the rectangular waveguide from round waveguide modes other than 

 circular electric. Additional evidence of deviations due to the coupling 

 between a plurality of waves was obtained; the rectangular-guide in- 

 sertion loss as a function of number of coupling elements did not increase 



