Microwave Engineering Questions and Answers – Quarter Wave Transformer(Smith Chart)

This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Quarter Wave Transformer(Smith Chart)”.

1. A quarter wave transformer is useful for matching any load impedance to a transmission line.
a) True
b) False
View Answer

Answer: b
Explanation: Quarter wave transformers are a simple circuit that can be used to match real load impedance to a transmission line. Quarter wave transformers cannot be used to match complex load impedances to a transmission line.

2. Major advantage of a quarter wave transformer is:
a) It gives proper matching
b) It gives high gain
c) Broader bandwidth
d) None of the mentioned
View Answer

Answer: c
Explanation: Quarter-wave transformers can be extended to multi section designs in a methodical manner to provide a broader bandwidth.

3. If a narrow band impedance match is required, then more multi section transformers must be used.
a) True
b) False
View Answer

Answer: b
Explanation: If a narrow band impedance match is required, then a single section of quarter wave transformer is used. When a wideband impedance match is required, then multi-section quarter wave transformers must be used for impedance matching.
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4. The major drawback of the quarter wave transformer that it cannot match complex load to a transmission line cannot be overcome.
a) True
b) False
View Answer

Answer: b
Explanation: The major drawback of the quarter wave transformer that it cannot match complex load to a transmission line can be overcome by transforming complex load impedance to real load impedance.

5. Complex load impedance can be converted to real load impedance by:
a) Scaling down the load impedance
b) By introducing an approximate length of transmission line between load and quarter wave transformer
c) Changing the operating wavelength
d) None of the mentioned
View Answer

Answer: b
Explanation: By introduction of a transmission line of suitable length between the load and the quarter wave transformer, the reactive component of the load that is the complex value can be nullified thus leaving behind only real load impedance to be matched.
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6. Converting complex load into real load for impedance matching has no effect on the bandwidth of the match.
a) True
b) False
View Answer

Answer: b
Explanation: Adding a length of line to the transmission line between the load and quarter wave transformer alters the frequency dependence of the load thus altering the bandwidth of the match.

7. If a single section quarter wave transformer is used for impedance matching at some frequency, then the length of the matching line is:
a) Is different at different frequencies
b) Is a constant
c) Is λ/2 for other frequencies
d) None of the mentioned
View Answer

Answer: a
Explanation: The length of the matching section is λ/4 for the frequency at which it is matched. For other frequencies, the electrical length varies. For multi section transformers, a wide bandwidth can be achieved.
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8. Quarter wave transformers cannot be used for non-TEM lines for impedance matching.
a) True
b) False
View Answer

Answer: a
Explanation: For non-TEM lines, propagation constant is not a linear function of frequency and the wave impedance is frequency dependent. These factors complicate the behavior of the quarter wave transformer for non-TEM lines.

9. The reactances associated with the transmission line due to discontinuities:
a) Can be ignored
b) Have to matched
c) Discontinuities do not exist
d) None of the mentioned
View Answer

Answer: b
Explanation: Reactance due to discontinuities in the transmission line contribute to the impedance, they can be matched by altering the length of the matching section.
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10. If a load of 10Ω has to be matched to a transmission line of characteristic impedance of 50Ω, then the characteristic impedance of the matching section of the transmission line is:
a) 50Ω
b) 10Ω
c) 22.36Ω
d) 100Ω
View Answer

Answer: c
Explanation: Characteristic impedance of the matching section of a transmission line is given by Z1=√Zₒ.ZL. Substituting the given impedance values, the characteristic impedance of the matching section is 22.36 Ω.

Sanfoundry Global Education & Learning Series – Microwave Engineering.
To practice all areas of Microwave Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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