This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Lossless Lines”.
1. The value of ‘α’ for a lossless line is:
d) Data insufficient
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
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:
Explanation: From the given inductive reactance and capacitive reactance, L and C are calculated using XL =2πfL and Xc = 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:
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:
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?
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:
b) ω √LC
c)1/ (ω √LC)
d) None of the mentioned
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
d) none of the mentioned
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?
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:
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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