Read the following statements : ST 1 : y-parameters can be obtained from Z parameters.
ST 2 : It is not necessary to define y-parameters separately.
ST 1 and ST 2 are correct.
ST 1 and ST 2 are correct — option (D), as recorded in the supplied key.
Statement 1 is certainly true. The admittance and impedance matrices of a two-port are inverses of one another :
\([Y]=[Z]^{-1}\)
and the conversion is explicit. Writing \(\Delta Z=Z_{11}Z_{22}-Z_{12}Z_{21}\),
\(Y_{11}=\dfrac{Z_{22}}{\Delta Z},\quad Y_{12}=\dfrac{-Z_{12}}{\Delta Z},\quad Y_{21}=\dfrac{-Z_{21}}{\Delta Z},\quad Y_{22}=\dfrac{Z_{11}}{\Delta Z}\)
So whenever the Z-parameters of a network are known and the matrix is non-singular, the Y-parameters follow by arithmetic alone with no further measurement.
Statement 2 follows from statement 1 on the key’s reading. If every Y-parameter can be computed from the Z-parameters, then a separate defining experiment for the Y set is not necessary — the same information is already present in the Z description, merely expressed in another basis. The two parameter sets describe one network, not two.
The qualification worth carrying, because it is the reason a careful candidate hesitates over ST 2. The conversion requires \(\Delta Z\neq 0\), and for some networks it is exactly zero — a series impedance in the through path has no finite Y description, and a shunt element has no finite Z description. Those cases are why all six parameter sets exist :
| Set | Independent variables | Natural use |
|---|---|---|
| Z (open-circuit impedance) | \(I_{1},I_{2}\) | Series-connected two-ports |
| Y (short-circuit admittance) | \(V_{1},V_{2}\) | Parallel-connected two-ports |
| h (hybrid) | \(I_{1},V_{2}\) | Transistor small-signal models |
| ABCD (transmission) | \(V_{2},I_{2}\) | Cascaded networks — matrices simply multiply |
The practical reason for defining Y separately is convenience rather than necessity: measuring Y requires short-circuit terminations while Z requires open-circuit ones, and at high frequency a good short is far easier to realise than a good open, which is why Y and S parameters dominate RF work.
Note. Read strictly — as a claim that the Y set never needs independent definition — ST 2 fails for the singular cases above, which would give option (A). The answer stored here follows the supplied key.
Similar Questions
Assertion (A) : In a two port network, with 4 terminals four types of parameters like impedance, admittance, hybrid and transmission are considered and they are related to each other.
Reason (R) : The assumption made for the above statement is that there are no independent sources and non-zero initial conditions within the linear port network.
Select your answer using the codes given below :
Match the given lists :
List – I List – II a. Condition of reciprocity i. \(\dfrac{Z_{12}}{Z_{22}}\) b. h12 ii. Z12 = Z21 c. 
\(\begin{bmatrix}R&R\\R&R\end{bmatrix}\)iii. Z d. Condition of symmetry iv. Z11 = Z22 Codes :
Important Questions from Two Port Networks
A Two - port network is reciprocal if and only if:
Read the following statements regarding two port networks.
(A) The condition of reciprocity and symmetry for a two-port network with 'g' parameter representation can be deduced from the interrelationship of 'h' and g parameters.
(B) The condition of reciprocity for the h parameter representation leads to the condition of reciprocity for 'g' parameters representation as g 12 = −g 21 .
(C) The condition of symmetry in h-parameters representation never leads to the condition of symmetry in 'g' parameters representation.
(D) The symmetry condition in 'h' and 'g parameter representation can be deduced by putting h 11 = g 11 .
Choose the correct answer from the options given below:
A passive 2-port network is in a steady-state. Compared to its input, the steady state output can never offer ________.
The condition for symmetric property of ABCD parameter of two port network is:
- When port 1 of two-port circuit is short-circuited, I 1 = 4I 2 & V 2 = 0.25 I 2 . Which of the following is true?
