

444 BELL SYSTEM TECHMC.IL JOURXAL 



The simulating and the compensating networks were de\ised from 

 purely theoretical studies of the characteristic impedance and ad- 

 mittance of periodically loaded lines as dependent on the frequency 

 and on the relative termination, in somewhat the same way as the 

 previously described ' networks for smooth lines were devised from 

 purely theoretical studies of the characteristic impedance of smooth 

 lines as dependent on the frecjuency. 



Building-out Structures, Basic Networks, and Excess-Simulators 



Although the characteristic impedance of a periodically loaded 

 line depends greatly on its relative termination {a or a'), yet there is 

 no need of attempting to devise various independent networks cor- 

 responding to various relative terminations of the line. For any net- 

 work that will simulate the line-impedance at any particular relative 

 termination can be "extended" or "built-out" to simulate it at any 

 other relative termination by merely supplementing the network 

 with an "extension network" or "building-out structure" in the 

 nature of an artificial line structure corresponding as closely as may 

 be necessary to the portion of actual line structure included between 

 the two relative terminations contemplated. Simulation can be 

 attained also by building-out the line instead of the network, or by 

 building-out both the line and the network to any common relative 

 termination; but in practice these alternatives are not usually per- 

 missible, the usual requirement being the simulation of a given fixed 

 line. (In present practice, the line is terminated usually at mid- 

 section [(r = 0.5], or as closely thereto as practicable.) 



The term "basic network" will be used to denote a network which 

 simulates the characteristic impedance of a non-dissipative periodically 

 loaded line without the network's containing in its structure any 

 building-out elements. Regarding the loaded line, the particular 

 relative termination to which the basic network pertains will be 

 termed the "basic relative termination" of the loaded line, and will 

 be denoted by <7(, or ai,' whenever a sj'mbol is needed for it. (For the 

 kinds of basic networks thus far devised, at, and at' lie between about 

 0.1 and about 0.2, that range ha\ing been found to include the rela- 

 tive terminations most favorable to the design of those kinds of 

 basic networks.) The foregoing terms, when used in connection with 

 a dissipative loaded line, will be understood to refer to the corre- 

 sponding non-dissipative loaded line. A considerable number of 

 kinds of basic networks will be described in Part \' supplemented 

 by Part VI. 



