IMPEDANCE CORRECTION OF WAVE FILTERS 



789 



we have thus far described produce sharp changes in reactance of the 

 attenuating region and are therefore unsuitable for such circuits. In 

 spite of their poor characteristics within the transmitting band, there- 

 fore, it has hitherto been necessary to use mid-shunt image impedance 

 terminations of the primitive "constant-^" type at junctions between 

 filters and modulators. Curve I of Fig. 19 for example, shows the 



TRANSMITTING 

 BAND "*~ 



'to infinity 



FREQUENCY 



ATTENUATING 

 BAND 



Fig. 19 — " Constant-yfe " and "m-derived" type Image impedances in the attenuating 



range. 



I — "m-derived" type image impedance. 



II — "Constant-^" type image impedance. 



impedance characteristic of an "m-type" section beyond the cutoff in 

 comparison with Curve II, representing the impedance of the "con- 

 stant-,^" type section in this range. The network configurations shown 

 in Fig. 12 however represent only one of two possible classes of sections 

 which can be developed as a result of the general analysis given in the 

 accompanying paper. The other class is radically different in configura- 

 tion. Networks of this second class may be advantageously substituted 

 for the "constant-^" sections formerly used with modulators. The 

 network characteristics in their attenuating regions approximate those 

 of the "constant-^ " sections and while they are not quite as good in the 

 transmitting region as the characteristics furnished by the networks of 

 Fig. 12 they are much better than the characteristics of the "constant 

 k" sections of Figs. A-A and 4-5. 



