Question 17.3: Find the admittance parameters of the two-port circuit in Fi......

A short circuit at port 2 connects admittances Y_{A} and Y_{B} in parallel. Hence, the admittance looking in at port 1 is y_{11} = Y_{A} + Y_{B}. The short-circuit current at port 2 is I_{2} = -Y_{B}V_{1}, hence y_{21} = -Y_{B}. A short circuit at port 1 connects Y_{B} and Y_{C} in parallel so the admittance looking in at port 2 is y_{22} = Y_{B} + Y_{C}. The short-circuit current at port 1 is I_{1} = -Y_{B}V_{2}, which means y_{12} = -Y_{B}. Thus, the admittance parameters of a general pi-circuit are

y_{11} = Y_{A} + Y_{B}
y_{21} = y_{12} = -Y_{B}
y_{22} = Y_{B} + Y_{C}