MAXIM ALLY -FLAT FILTERS IN WAVEGUIDE 



699 



It can be shown readily that the frequency parameter can be expressed 

 in terms of the wavelength, thus 



(i-7)-(t:-x-:)fe)fe) <»' 



where Xa is the wavelength in free space. 



For narrow percentage bands, this reduces to the approximate relation 



20 



in _o 



^ -5 



O -4 



z 



U 

 ^-2 



3 4 5 6 8 10 20 30 40 50 60 80 100 



SELECTIVITY (LOADED Q) 



200 300 



Fig. 11 — The relation between loaded Q and normalized susceptance. (Inductive ob 

 stacks) 



This states, in effect, that the percentage bandwidth is greater in terms of 

 wavelength than in terms of frequency, by the square of the ratio of the 

 wavelengths in the guide and in free space. The selectivity in terms of the 

 frequencies and wavelength ratio thus becomes 



1 /Xao\' /O '^ -^' 



1 /XooV ^ /o /XooV 



V/o fJ 



(38) 



This is the selectivity that is plotted as a function of B in Figures 11 and 12. 

 Excess Phase and Connecting Lines 



The excess phase of this type of cavity is taken into account by adding the 

 lengths of line, f (see Fig. 9), which have a length given by the relation (See 

 Appendix I) 



tan 





(39) 



