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

1. The value of ‘α’ for a lossless line is:

a) 0

b) 1

c) Infinity

d) Data insufficient

View Answer

Explanation: α-for a transmission line signifies the attenuation constant. For a lossless transmission line attenuation constant is zero and the propagation occurs without losses.

2. If propagation constant is 12:60°, then the value of phase constant and attenuation constant is:

a) α=6, β=10.39

b) α=61, β=78

c) α=12, β=20.6

d) none of the mentioned

View Answer

Explanation: The given propagation constant is in polar form .converting from polar form to rectangular form and equating the real and imaginary parts, we get α=6 and β=10.39.

3. If a transmission line with inductive reactance of 41.97 Ω and capacitive reactance of 1132.5Ω is operated at 1 GHz , then its phase constant is:

a) 0.0305

b) 0.3

c) 30.3

d) 0.6

View Answer

Explanation: From the given inductive reactance and capacitive reactance, L and C are calculated using X

_{L}=2πfL and X

_{c}= 1/2πfC. β=ω√LC, substituting the calculated L and C, we get β=0.0305.

4. The expression for a phase velocity of a transmission line is:

a) √LC

b) 1/√LC

c) X_{L}+X_{c}

d) X_{L}/X_{c}

View Answer

Explanation: The expression for phase velocity is derived from known basic transmission line equations and the derived equation comes out to be 1/√LC .

5. If the admittance and the impedance of a transmission line are 100 Ω and 50 Ω of a respectively, then value of phase constant β is:

a) 0

b) 20

c) 132

d) 50

View Answer

Explanation: β=ω√LC. Since both the line impedance and line admittance are both real, there is no phase difference caused and hence substituting in the above equation, we get β=0.

6. For a lossless line, which of the following is true?

a) γ=jβ

b) γ=α

c) γ=α+jβ

d) γ=α*jβ

View Answer

Explanation: For a lossless line, attenuation constant α is 0. Hence substituting α=0 in γ=α+jβ, we get γ= jβ.

7. Expression for phase constant β is:

a) √LC

b) ω √LC

c)1/ (ω √LC)

d) None of the mentioned

View Answer

Explanation: From the equation of γ in terms of Z and Y(impedance and admittance of the transmission line respectively), expanding the equation and making certain approximations, β= ω √LC.

8. A microwave generator at 1.2 GHz supplies power to a microwave transmission line having the parameters R=0.8Ω/m, G=O.8millisiemen/m, L=0.01µH/m and C=0.4PF/m. Propagation constant of the transmission line is:

a) 0.0654 +j0.48

b) 0.064+j4.8

c) 6.4+j4.8

d) none of the mentioned

View Answer

Explanation: Z=R+jωL and Y=G+jωC, hence finding out Z and Y from these equations, substituting in γ=√ZY, value of γ is found out to be 0.0654+j0.48.

9. In a certain microwave transmission line, the characteristic impedance was found to be 210 10°Ω and propagation constant 0.2 78°.What is the impedance Z of the line, if the frequency of operation is 1 GHz?

a) 0.035+j41.97

b) 0.35+j4.97

c) 35.6+j4.28

d) 9.254+j4.6

View Answer

Explanation: Impedance Z of a transmission line is given by the product of propagation constant γ and characteristic Zₒ, Z= γZₒ , we get Z=0.035+j41.97.

10. For a transmission line, L=1.8mh/m C=0.01pF/m, then the phase constant of the line when operated at a frequency of 1 GHz is:

a) 4.2426

b) 2.2

c) 0.3

d) 1

View Answer

Explanation: Formula to calculate the phase constant β is β=ω√LC.substituting the given values of L,C and f, the value of β is 4.2426.

**Sanfoundry Global Education & Learning Series – Microwave Engineering.**

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