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BELL SYSTEM TECHNICAL JOURNAL 



quency and length. With this understanding, if the frequency band to be 

 covered by the tunable cavity extends from/i to/2 then the length must be 

 adjustable from Li to Lo. Responses to frequencies within the band, but 



O 



g 0.5 



< 



'^ 0.4 



1.5 

 D 



Fig. 2 — Mode-shape factors ( (>- j as a function of diameter to length ratio ( y I 

 cuiar c\-linder resonator — T.\I modes. 



for cir- 



which demand lengths outside the range Li to Li are of little interest because 

 mechanical stops prohibit other lengths. On the assumption that the ap- 

 plied frequency will alw'ays lie within the operating band/i to/2, responses 

 to frequencies below /i or above /o are likewise of little interest. Therefore, 



