This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Terminated Lossless Transmission Lines – 1”.

1. When a lossless line is terminated with an arbitrary load impedance Z_{L}, then it :

a) causes wave reflection on transmission lines

b) transmits the entire supplied power

c) causes loss in transmission line

d) none of the mentioned

View Answer

Explanation: When a line is terminated with a impedance other the characteristic impedance of the transmission line, It results in reflection of waves from the load end of the transmission line hence resulting in wave reflection in the transmission line.

2. We say a transmission line is matched when:

a) Z_{L}=Z_{0}

b) Z_{L}=√Z_{0}

c) Z_{L}=Z_{0}/2

d) Z_{L}=2Z_{0}

View Answer

Explanation: We say a line is matched only when the characteristic impedance of the transmission line is equal to the terminating load impedance. Hence condition for a line to be matched is Z

_{L}=Z

_{0}.

3. Voltage reflection coefficient can be defined as:

a) ratio of amplitude of reflected voltage wave to the transmitted voltage wave

b) ratio of amplitude of reflected voltage to the incident voltage wave

c) ratio of load impedance to the characteristic impedance of the transmission line

d) none of the mentioned

View Answer

Explanation: From transmission line theory, reflection co-efficient of a transmission line is defined as the ratio of amplitude of reflected voltage to the incident voltage wave.

4. Expression for a voltage reflection co-efficient in terms of load impedance and characteristics impedance is:

a) (Z_{L}– Z_{0})/(Z_{L}+ Z_{0})

b) (Z_{L}+ Z_{0})/(Z_{L}– Z_{0})

c) Z_{L}. Z_{0}/( Z_{L}+ Z_{0})( Z_{L}-Z_{0})

d) (Z_{L}+ Z_{0})( Z_{L}-Z_{0})/ Z_{L}. Z_{0}

View Answer

Explanation: The amplitude of the reflected voltage wave at the load end is equal to the difference between the load and the characteristic impedance, incident voltage is proportional to the sum of the load and characteristic impedance.

5. If a transmission line of a characteristics impedance 50 Ω is terminated with a load impedance of 100 Ω, then the reflection co efficient is:

a) 0.3334

b) 0.6667

c) 1.6

d) 1.333

View Answer

Explanation: Expression for reflection co-efficient of a transmission line is (Z

_{L}– Z

_{0})/(Z

_{L}+ Z

_{0}) .substituting the given values of load and characteristic impedance, we get reflection co-efficient equal to 0.3334.

6. Return loss for a transmission line in terms of its reflection co efficient is given by:

a) -20logl┌l in dB where ┌ is the reflection coefficient.

b) -10logl┌l in dB where ┌ is the reflection coefficient

c) -10log (1/l┌l) in dB where ┌ is the reflection coefficient

d) -20log (1/l┌l) in dB where ┌ is the reflection coefficient

View Answer

Explanation: Return loss signifies the amount of energy reflected back from the load which is proportional to the reflection co-efficient of the line. Return loss in dB is given by the logarithm of the reflection co-efficient.

7. If the reflection coefficient for transmission line is 0.24, then the return lossin dB is:

a) 12.39dB

b) 15dB

c) -12.39dB

d) -15.2dB

View Answer

Explanation: The return loss of a transmission line, given the reflection co-efficient is -20logl┌l in dB where ┌ is the reflection co-efficient. Substituting for reflection co-efficient in the above equation, return loss is 12.39dB.

8. Expression for VSWR in terms of reflection co-efficient is:

a) (1+│┌│)/(1-│┌│)

b) (1-│┌│)/(1+│┌│)

c) 1/│┌│

d) 1/1+│┌│

View Answer

Explanation: VSWR is the ratio of maximum amplitude of the standing wave formed to the minimum amplitude of the standing wave, when these voltages are expressed in terms of reflection co-efficient, we get the expression(1+│┌│)/(1-│┌│).

9. If the reflection co-efficient for a transmission line is 0.3, then the VSWR is:

a) 0.5384

b) 1.8571

c) 0.4567

d) 3.6732

View Answer

Explanation: VSWR (voltage standing wave ratio) in terms of reflection co-efficient is given by (1+│┌│)/(1-│┌│).substituting ┌=0.3 in this equation we get, VSWR=1.8571.

10. If a transmission line of characteristic impedance 50 Ω is terminated with a load impedance of 150 Ω, then VSWR is:

a) 0.75

b) 0.5

c) 2

d) none of the mentioned

View Answer

Explanation: VSWR (voltage standing wave ratio) in terms of load and characteristic impedance is given by Z

_{L}– Z

_{0}/Z

_{L}+ Z

_{0}. Substituting for Z

_{L}and Z

_{0}in the above equation, VSWR is 0.5.

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