Combination of Two Port Networks

• Series connection of two 2-port networks: Z = Z1 + Z2
• Parallel connection of two 2-port networks: Y = Y1 + Y2
• Cascade connection of two 2-port networks: A = A1 . A2

Reciprocal and Non reciprocal Networks :A two port network is called reciprocal if the open circuit transfer impedances are equal Z12 =Z21 . Consequently, in a reciprocal two port network with current I feeding oe port , the open circuit voltage measured at other port is the same, irrespective of the ports. The voltage is equal to V = Z12*I = Z21*I. Networks containing resistors,inductors and capacitors are generally reciprocal. Networks that additionally have dependent sources are generally nonreciprocal.
Z parameters in terms of remaining parameters given by :

where D is the determinant of the corresponding matrix.
For examples and more details visit the site given below :
http://fourier.eng.hmc.edu/e84/lectures/ch3/node11.html