606 



BELL SYSTEM TECHNICAL JOURNAL 



The four parameters Z are of simple physical significance and it follows 

 that: 



Zii is the input impedance with output open 



— Z22 is the output impedance with input open 



— Z12 is the feedback impedance with input open 

 Z21 is the transfer impedance with output open. 



The relations between the j8's and the Z's are given by the expressions: 



Z22 



where 



We have also 



^11 = 



i3l2 = 



Z12 



a7 



R ^21 



P21 = — — - 



Az 



1822 = 



Zn 



Z21 



Z12 

 Z22 



(21) 



(22) 



where 



Az = 



Afl 



^^ = 



/321 /322 



(23) 



(24) 



Applying now to (20) the transformations which led to the networks of 

 Figs. 9, 10 and 12, we get the networks of Figs. 13, 14 and 15. 



The "passive part" of the network in Fig. 13 reproduces the two open 

 circuit impedances Zn and Z22 as well as the feedback impedance Z12 of the 

 complete network. 



The network in Fig. 14 differs from that of Fig. 13 because of the use of the 

 transfer impedance Z21 in the ''passive part" with the result that the im- 

 pressed current appears on the input side. 



