250+ TOP MCQs on Terminated Lossless Transmission Lines – 2 and Answers

Microwave Engineering Interview Questions on “Terminated Lossless Transmission Lines – 2”.

1. Expression for input impedance of a transmission line in terms of load impedance and characteristic impedance is:
A. Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl)
B. (Z₀+j Z_Ltan βl)/ (Z_L+j Z₀tan βl)
C. Z₀ (Z_L-j Z₀tan βl)/ (Z₀-j Z_Ltan βl)
D. (Z₀-j Z_Ltan βl)/ (Z_L-j Z₀tan βl)
Answer: A
Clarification: Representing the input voltage as the ratio of voltage at current, representing voltage and currents in hyperbolic function form and simplifying, we get Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl).

2. Input impedance of a short circuited transmission line is :
A. -jZ₀tanβl
B. jZ₀tanβl
C. jZ₀cotβl
D. – jZ₀cotβl
Answer: B
Clarification: Since the load impedance of a short circuited transmission line is zero, substituting ZL=0 in the expression for input impedance of a transmission line Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl), input impedance of the transmission line comes out to be jZ₀tanβl.

3. Input impedance of a transmission line can be represented in terms of this simple trigonometry function.
A. sine function
B. cosine function
C. cotangent function
D. tangent function
Answer: D
Clarification: The input impedance of a transmission line is expressed in the standard form as Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl) which is represented in terms of a tangent function.

4. If a ƛ/3 transmission line is short circuited that has a characteristic impedance of 50 Ω, then its input impedance is:
A. -j100Ω
B. 50Ω
C. 86.60Ω
D. –j86.60Ω
Answer: D
Clarification: For a short circuited transmission line, the input impedance is given by jZ₀tanβl.substituting for characteristic impedance and ‘l’ in the above equation, input impedance is –j86.60Ω.

5. Expression for input impedance of an Open circuited transmission line is:
A. -jZ₀tanβl
B. jZ₀tanβl
C. jZ₀cotβl
D. -jZ₀cotβl
Answer: D
Clarification: Since the load impedance of a open circuited transmission line is infinity, substituting ZL=infinity (1/ Z_L =0) in the expression for input impedance of a transmission line Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl), input impedance of the open circuited transmission line comes out to be- jZ₀cotβl.

6. Input impedance of a open circuited transmission line is represented using this trigonometric function:
A. sine function
B. cosine function
C. cotangent function
D. tangent function
Answer: C
Clarification: The input impedance of a transmission line is expressed in the standard form as Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl). With Z_L equal to infinity for open circuit termination, 1/ Z_L equal to 0, substituting this, we get input impedance in terms of a cotangent function.

7. For a λ/2 transmission line, if the characteristic impedance of the line is 50 Ω and the terminated with a load of 100 Ω, then its input impedance is:
A. 100Ω
B. 50Ω
C. 88.86Ω
D. none of the mentioned
Answer: A
Clarification: Input impedance of a transmission line is given by Z₀ (Z_L+j Z₀tan βl)/ (Z₀+j Z_Ltan βl). Substituting β=2π/λ, and l=λ/2, we get input impedance of the transmission line equal to the load impedance or the terminated load.

8. If a λ/3 transmission line is open circuited and has characteristic impedance of 50 Ω then the input impedance is:
A. j28.86Ω
B. 50Ω
C. j50Ω
D. 28.86Ω
Answer: A
Clarification: Input impedance of an open circuited transmission line is given by – jZ₀cotβl. Substituting l=λ/3 and β=2π/λ in the above equation, input impedance is j28.86Ω.

9. Expression for a transmission co-efficient of a transmission line is :
A. 2Z_L/ ( Z_L+Z₀)
B. (Z_L-Z₀)/ (Z_L+Z₀)
C. 2Z₀/( Z_L+Z₀)
D. (Z_L+Z₀)/ (Z_L-Z₀)
Answer: A
Clarification: T=┌+1, where T is the transmission co-efficient and ┌ is the reflection co-efficient substituting ┌= (Z_L-Z₀)/ (Z_L+Z₀) in the equation for transmission co-efficient, we get 2Z_L/ ( Z_L+Z₀).

10. For a transmission line, if the reflection coefficient is 0.4, then the transmission coefficient is:
A. 0.4
B. 1.4
C. 0.8
D. 2.8
Answer: B
Clarification: T=┌+1, where T is the transmission co-efficient and ┌ is the reflection co-efficient substituting ┌=0.4 in the above equation, transmission co-efficient is equal to 1.4.

11. If the transmission coefficient of a transmission line is 1.6, then the reflection co efficient is:
A. 0.8
B. 0.6
C. 0.4
D. 0.3
Answer: B
Clarification: T=┌+1, where T is the transmission co-efficient and ┌ is the reflection co-efficient substituting T=1.6, we get ┌=0.6.

12. For a transmission line, if the transmission coefficient is 1.4, then the insertion loss in dB is:
A. -2.922dB
B. 29dB
C. 1.46dB
D. -29dB
Answer: A
Clarification: Insertion loss for a transmission line is given by the expression -20loglTl in dB. Substituting T=1.4 and taking logarithm to base 10, insertion loss is -2.922dB.

13. The relation between nepers and decibels is:
A. 1 Np= 8.686 dB
B. 1 dB=8.868 dB
C. Np≥dB
D. dB≥Np
Answer: A
Clarification: 1 Np=10log e² dB. Substituting e=2.718 in the above equation , 1Np=8.686 dB.