IMPEDANCE CORRECTION OF WAVE FILTERS 



781 



them, could be used only with complementary filters (i.e. low-pass 

 and high-pass, or band-pass and band-elimination). In U, S. Patent 

 No. 1616193 R. H. Mills specifically applies the method to band pass 

 filters. Mills, proceeding from the fact that the adjacent sides of two 



n^^ 



W — ^w- 



7L 

 IT 



1L 



Fig. 10 — Schematic of band-pass filters with auxiliary network, 

 coefficient of these filters is given by curve I of Fig. 11. 



The reflection 



band pass filters behave somewhat like complementary filters, while 

 complementary filters are absent on the further sides of the bands, 

 shunted simple networks, approximating the impedances of the missing 

 complementary filters, across the parallel filter system. The filters of 

 the Type D carrier telephone system ^ incorporated this device. 



30 



z 

 u 

 o 



a. 



Ui 

 Q. 



25 



20 



Z 



o 



o 

 u 



z 

 o 

 I- 

 o 

 u 

 _J 

 \j. 

 us 

 a. 



10 



6 7 8 9 



FREQUENCY IN KILOCYCLES PER SECOND 



10 



Fig. 1 1 — Reflection coefficient of a set of band-pass filters. 

 I — For partially corrected .v-terminated filters. 

 II — For uncorrected x-terminated filters. 

 Ill — For filters using the termination of Fig. 12-B modified for parallel operation. 



* The general engineering features of this system are discussed in the Transactions 

 of the A. I.E. £., Vol. 48, No. 1, pp. 117-139. 



