704 



BELL SYSTEM TECHNICAL JOURNAL 



Inductive Posts 



The normalized susceptance of the round cyhndrical inductive post, cen- 

 trally located in the waveguide parallel to the electric vector, may be calcu- 

 lated from the approximate formula"- ^^' ^^ 



B = 



2\ 



1 



' - (1.) 



where a is the width of the guide, and d is the post diameter. 



(47) 



20 



.-10 

 a -9 



< 



Q- -5 



UJ 



< 



0.003 0.005 



0.02 0.03 0.04 0.06 0.08 0.1 



a 



0.2 0.3 



Fig. 17 — Experimentally determined curve of normalized susceptance of inductive posts 



The experimentally determined values of susceptance are somewhat less 

 than the values calculated by the formula (47). The difference is less than 



20% when - is less than 0.08. A curve of experimentally determined values 



is plotted in Fig. 17, the data being taken in rectangular waveguide 0.872'' X 

 1.872" at a frequency near 4000 mc* 



The normalized susceptance of posts is also a function of their position in 

 the waveguide, the susceptance decreasing as the posts are moved off center. 

 This feature may be used when it is desired to make all the posts in a filter 



* Data supplied by Mr. A. E. Bowen of Bell Telephone Laboratories. 



