MViv.M. ixiHCT.ixcn ix ir.iir. rii.iiRs 65 



chanirtiTistics is <>ut>i(lo tin- so>|h- of this |).i|)(t r\rn lltoiiuli rn.iiiy 

 i)f till" structuros listi-<l in Tahlc II will show, il c-oinpii-toiy aiuily/cd, 

 nnilti-l)aiul charaiterislirs. Where no specific charadorishcs are 

 listed in TaMe II, no low pass, hijjh pass, single i)an(l pass, or single 

 band elimination characteristics are ohtainaWe with a filter section 

 limited to six different reactance elements. 



In Table II, a larjje number of the structures ha\e identically the 

 same types of attenuation constant and phase constant characteris- 

 tics. For example, six of the seven low pass filter sections have at- 

 tenuation constant and phase constant characteristic No. 2 of Fig. 7. 

 Likewise, six of the high pass structures have attenuation constant and 

 phase constant characteristic No. 4. Also, in Table 11, band pass 

 groups are to be found having respectively, the following propagation 

 characteristics common to each group: G, 7, 8, 9, 10, II and 12. Finally, 

 ten of the eleven band elimination structures listed ha\e propagation 

 constant characteristic No. 14. 



Although six of the se\en low pass wa\e fillers ha\e ihc same at- 

 tenuation constant and phase constant characteristics, the various 

 image impetlancc characteristics differentiate the structures among 

 themselves. Similar differentiations exist in the high pass, band pass, 

 and band elimination groups of structures. In each of the four tyfjes 

 of filter sections however, all of those structures having the same series 

 reactance meshes (that is, having the same series configuration of 

 reactance elements) may be designed to have the same mid-series 

 image impedance characteristic and, similarly, all of those structures 

 within each type having the same shunt reactance meshes, or con- 

 figuration of elements, may be designed to have the same mid-shunt 

 image impedance characteristic. 



In view of the fact that some of the structures listed in Table II 

 have the same attenuation and phase constants but have different 

 impedance characteristics, the question arises as to the relative virtues 

 of the latter. F'urthermore, since certain of the structures have 

 the same mifl-series or mid-shunt image impedances but have different 

 propagation characteristics, it is possible to join together such struc- 

 tures and obtain a composite structure which has no internal reflection 

 losses, that is, one whose total transfer constant is the siuii of the 

 various transfer c()nstants of the indi\'idual sections. In order to 

 minimize reflection and interaction losses in the transmission range, 

 it is generally desirable to use, at the terminals of the filler, sections 

 whose image impedances closely simulate those of the terminal im- 

 pedances to which the filter is connected. The choice presented by 



