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BELL SYSTEM TECHNICAL JOURNAL 



an impedance characteristic beyond the band almost as good as that 

 of the "constant-yfe" filter. Within the transmitting band, of course, 

 its impedance is much better than that of the normal filter section. 



Attenuation Characteristics of Terminating Sections 

 In the practical application of either type of terminating section 

 some others of their characteristics, such as their transmitting efficiency 

 and the effect produced upon them by parasitic dissipation of energy 

 in the network elements, are also of importance. The transmission 

 characteristics of the networks can be determined roughly by com- 

 paring them with standard filter sections. Let us consider, for exam- 

 ple, the two branch termination shown in Fig. 20. If we neglect for 



^OF m- 



-derived'^^ection'^ 4 OF '"constant -k" 



SECTION 



Fig. 20 — Figure illustrating approximate transmission characteristics of 2-branch 



terminations. 



the moment the third element of the susceptance correcting network, 

 the remainder of the structure can be divided, in the manner indicated 

 by the broken lines, into two portions, one of which resembles half of 

 a "constant-/^" section and the other half of an "m-derived" section 

 in physical configuration. The transmission characteristic of the 

 actual network is substantially similar to that which would be furn- 

 ished by standard filter sections of these types. The mere fact that 

 the network functions as an impedance corrector is, of course, sufficient 

 to show that it will transmit efficiently frequencies within the nominal 

 transmission band of the filter. Beyond the transmission band the 

 attenuation characteristic would be almost exactly coincident with 

 that of the suggested filter equivalent if it were not for the extra element 

 in the final shunt branch. The extra element produces an anti- 

 resonance in this arm somewhat beyond the resonance and near the 

 anti-resonance point the attenuation is somewhat less than that which 

 would be secured from ordinary filter sections. On the other hand the 



