IMPEDANCE CORRECTION OF WAVE FILTERS 



791 



Moreover, their attenuation characteristics can be varied within fairly 

 wide limits without appreciably affecting the impedance characteristics 

 we obtain. If we make allowance beforehand for the attenuation of 

 the terminations, therefore, the number of sections making up the 

 main body of the filter can be correspondingly reduced. These rela- 

 tions are illustrated by Figs. 20, 21 and 22 which are drawn for termina- 

 tions having the configuration of Fig. \2-B. The network attenuation 

 is compared in each case with the attenuation of the most nearly equiv- 



36 



32 



28 



24 

 Si 

 T3 



?20 



o 



2 



o 

 i- 



in 



z 



16 



12 



10 II 1.2 1.3 1,4 15 1.6 17 18 1.9 2.0 2 I 



X 



Fig. 22 — Insertion loss of a 2-branch termination. 



alent filter structure. The corresponding modifications in the im- 

 pedance characteristic of the network are shown by Curves II, III and 

 IV of Fig. 13. The real component (Curve I) of the impedance is the 

 same in all cases, since the adjustment of the attenuation character- 

 istic was produced entirely by manipulating the final series branch 

 of the network, which has no effect on this component. When low- and 

 high-pass filters are involved the terminating networks contain one 

 more element than the suggested filter equivalent. This much must be 

 conceded to the cost of impedance correction. It will be observed, 

 however, that the remaining elements contribute almost as much at- 

 tenuation as they would in standard filter sections. Indeed at fre- 



