MAXIMALLY-FLAT FILTERS IN WAVEGUIDE 



703 



Capacitive Irises 



The normalized susceptance of infinitely thin capacitive obstacles, as illus- 

 trated in Fig. 14, may be calculated by the approximate relation^^ 



B = - log. cosec — 



\n lb 



(45) 



where b is the height of the waveguide, X^ is the wavelength in the waveguide, 

 and d is the width of the iris opening. 



-200 



-100 

 -80 



-60 

 -40 



-20 



-10 

 -8 



-6 



-4 



-2 



-1.0 

 -0.8 



0.05 0.10 0.15 0,20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 



d. 

 a 



Fig. 16 — Experimentally determined curve of normalized susceptance of inductive irises. 



As with the inductive vanes, the normahzed susceptance is a function of 

 the iris thickness and may be calculated from the approximate formula^^ 



^ = i5o + 



llTT 



C-0 



(46) 



where Bq is the normahzed susceptance of the infinitely thin iris, and r is 

 the iris thickness. 



For best results, the irises should be designed from experimentally deter- 

 mined curves, however. 



