# Microwave Engineering Questions and Answers – Field Analysis of Transmission Lines

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This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Field Analysis of Transmission Lines”.

1. In a two wire transmission line, if the distance between the lines is 20 mm and the radii is 5 mm then the inductance of the line is:
a) 0.1 µH
b) 0.526 µH
c) 0.9 µH
d) 1 µH

Explanation: The inductance of a two wire transmission line is given by the equation µ*ln(b/a)/2π. Substituting the given values in the above equation, inductance is 0.526 µH.

2. In a two wire transmission line , if the distance between the lines is 60mm and the radii is 10 mm , then the capacitive reactance of the line when operated at 12.5 GHz is
a) 20 pF
b) 21.13 pF
c) 23 pF
d) 12 pF

Explanation: The capacitive reactance of a two wire transmission line is π∈/cosh-1(D/2a). substituting the given values in the above expression, the capacitive reactance is 21.13 pF.

3. For a parallel plate type of a transmission line, then expression for conductance of the line is:
a) ∈(ω)w/d
b) 2Rx/x
c) μ/2π ln⁡(w/d)
d) μ/π cosh-1(w/2d)

Explanation: The conductance of a parallel plate waveguide is dependent on the complex value of the permittivity, width of the waveguide and the distance between the waveguide plates.
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4. One of the Maxwell‘s curl equation that is satisfied inside a coaxial line is:
a) ∇×E =-jωµ (vector H)
b) ∇×E =-jωμ(vector E)
c) ∇×H=-jωμ(vector H)
d) ∇×H=jωμ(vector H)

Explanation: ∇×E = -jωµ (vector H).This is the Maxwell’s equation satisfied by the electric and magnetic fields inside a waveguide.

5. The wave impedance of air for a wave propagating in it is:
a) 377 Ω
b) 345 Ω
c) Insufficient data
d) None of the mentioned

Explanation: Intrinsic impedance is the impedance offered by air for a wave propagating in it. This is a standard value and is 377 Ω.

6. Wave impedance of a wave travelling in a medium of a relative permittivity 2 and permeability 4 is
a) 188.5 Ω
b) 200 Ω
c) 300 Ω
d) None of the mentioned

Explanation: Intrinsic impedance of a medium is given by the expression √μ/ϵ. Substituting the given values in the above expression, the wave impedance is 188.5 Ω.

7. For a parallel plate transmission line, if w= 12 mm and the distance between the plates is 2 mm, then the inductance of the transmission line is:
a) 0.2 µH
b) 0.1 µH
c) 0.3 µH
d) 0.4 µH

Explanation: The inductance of a parallel plate transmission line is given by µd/W. substituting the given values in the above expression, the inductance is 0.2 µH.

8. Expression for capacitance of a two wire transmission line is
a) ∈’*π/cosh⁡-1(D/2a)
b) μ/π*cosh-1(D/2a)
c) 2π∈/ln⁡(D/2a)
d) ∈”*πω/cosh-1(D/2a)

Explanation: The expression for capacitance of a two wire transmission line is ∈’ π/cosh-1(D/2a). Capacitance of a two wire transmission line is dependent on the distance between the two lines and the radius of the line.

9. If the distance between the 2 wires in a 2 wire transmission line is 10 mm and the radii 2 mm, then the inductance of the transmission line is:
a) 0.62 µH
b) 1 µH
c) 2 µH
d) None of the mentioned

Explanation: The inductance of a two wire transmission line is given by the expression µcosh-1(D/2a)/π. Substituting the given values in the above expression, the inductance is 0.62 µH.

10. For a parallel plate transmission line, if the complex part of permittivity is 2.5, if the width is 100 mm and the distance between the plates is 10 mm, then the conductance of the transmission line is:
a) 25 Ʊ
b) 30 Ʊ
c) 45 Ʊ
d) None of the mentioned

Explanation: Conductance of a parallel plate transmission line is ∈W/d. substituting the given values in the above expression, the conductance of the transmission line is 25 Ʊ.

11. For a parallel plate transmission line, if the series resistance is 10 mΩ/m, and the width is 100 mm, then the resistance of the transmission line is:
a) 0.2 Ω
b) 1 Ω
c) 2 Ω
d) 5 Ω