This set of Microwave Engineering Assessment Questions and Answers focuses on “Impedance and Admittance Matrices”.

1. The one below among others is not a type TEM line used in microwave networks:
a) Co-axial wire
b) Micro strip line
c) Strip lines
d) Surface guide

Explanation: Coaxial micro strip and strip lines all support TEM mode of propagation through them. But surface guides do not support TEM mode of propagation in them. Hence it cannot be called a TEM line.

2. The one below is the only micro wave network element that is a TEM line:
a) Co-axial cable
b) Rectangular wave guide
c) Circular wave guide
d) Surface wave guide

Explanation: Coaxial cables support TEM mode of propagation in them and rectangular waveguide, circular wave guide, surface waveguides do not support TEM mode of propagation in them.

3. The relation between voltage, current and impedance matrices of a microwave network is:
a) [V] = [Z][I]
b) [Z] = [V][I]
c) [I] = [Z][V]
d) [V] = [Z]-[I]

Explanation: In microwave networks, at any point in a network, the voltage at a point is the product of the impedance at that point and current measured. This can be represented in the form of a matrix.

4. The relation between voltage, current and admittance matrices of a microwave network is:
a) [I] = [Y] [V]
b) [Y] = [V] [I]
c) [I] = [Z] [V]
d) [V] = [Z]-1[I]

Explanation: The relation between voltage current and admittance matrices is [I] = [Y] [V]. here I represents the current matrix, Y is the admittance matrix and V is the voltage matrix.

5. Admittance and impedance matrices of a micro waves network are related as:
a) [Y] = [Z]-1
b) [Y] = [Z]
c) [V] = [Z] [Z]-1
d) [Z] = [V] [V]-1

Explanation: Both admittance and impedance matrix can be defined for a microwave network. The relation between these admittance and impedance matrix is [Y] = [Z]-1. Admittance matrix is the inverse of the impedance matrix.
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6. The element of a Z matrix, Zij can be given in terms of voltage and current of a microwave network as:
a) ZIJ = VI/IJ
b) ZIJ = VIIJ
c) 1//ZIJ = 1/JIVI
d) VIJ = IJ/JI

Explanation: The element Zij of a Z matrix is defined as the ratio of voltage at the ith port to the current at the jth port given that all other currents are set to zero.

7. In a two port network, if current at port 2 is 2A and voltage at port 1 is 4V, then the impedance Z₁₂ is:
a) 2 Ω
b) 8 Ω
c) 0.5 Ω
d) Insufficient data

Explanation: Z12 is defined as the ratio of the voltage at port 1 to the current at port 2. Substituting the given values in the above equation, Z12 parameter of the network is 2 Ω.

8. In a 2 port network, if current at port 2 is 2A and voltage at port 1 is 4 V, then the admittance Y₂₁ is:
a) 0.5 Ʊ
b) 8 Ʊ
c) 2 Ʊ
d) 4 Ʊ

Explanation: Admittance parameter Y12 is defined as the ratio of current at port 1 to the voltage at port 2. Taking the ratio, the admittance Y12 is 0.5 Ʊ.

9. For a reciprocal network, Z matrix is:
a) A unit matrix
b) Null matrix
c) Skew symmetric matrix
d) Symmetric matrix

Explanation: For a reciprocal matrix, the impedance measured at port Zij is equal to the impedance measured at port Zji. Since these parameters occupy symmetric positions in the Z matrix, the matrix becomes symmetric.

10. For a lossless network, the impedance and admittance matrices are:
a) Real
b) Purely imaginary
c) Complex
d) Rational

Explanation: For a network to be lossless, the network should be purely imaginary. Presence of any real component implies the presence of resistance in the network from which the network becomes lossy. So the matrices must be purely imaginary.

11. The matrix with impedance parameters Z₁₁=1+j, Z₁₂=4+j, Z₂₂=1, Z21=4+j is said to be
a) Reciprocal network
b) Lossless network
c) Lossy network
d) None of the mentioned

Explanation: In the given case, Z12=Z21. This condition can be satisfied only by reciprocal networks. Hence the given network is a reciprocal network.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
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