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

1. A single section tapered line is more efficient in impedance matching than a multisection tapered line for impedance matching.

a) True

b) False

View Answer

Explanation: As the number N of discrete transformer sections increases, the step changes in the characteristic impedance between the sections become smaller, and the transformer geometry approaches a continuous tapered line. Thus multisection are preferred over single section for impedance matching.

2. Passband characteristics of tapered lines differ from one type of taper to another.

a) True

b) False

View Answer

Explanation: The impedance of the tapered line varies along the line depending on the type of the tapering done. Thus impedance is a function of the type of taper. Hence passband characteristics depend on the type of taper.

3. For a continually tapered line, the incremental reflection co-efficient is:

a) ∆Z/2Z

b) 2Z/∆Z

c) ∆Z_{0}/2Z_{0}

d) None of the mentioned

View Answer

Explanation: The incremental reflection co-efficient ∆Г is a function of distance. If a step change in impedance occurs for z and z+∆z, then the incremental reflection co-efficient is given by ∆Z/2Z.

4. The variation of impedance of an exponentially tapered line along the length of the line is given by:

a) Z(z)=Z_{0}e^{az}

b) Z(z)=Z_{0}e^{-az}

c) Z(z)=Z_{0}e^{2az}

d) Z(z)=Z_{0}e^{-2az}

View Answer

Explanation: The variation of impedance along the transmission line is a positive growing curve and is given by Z(z)=Z

_{0}e

^{az}. The constant ‘a’ is defined as L-1 ln(Z

_{L}/Z

_{0}).

5. The value of constant ‘a’ for an exponentially tapered line of length 5 cm with load impedance being 100Ω and characteristic impedance of the line is 50Ω is:

a) 0.1386

b) 0.265

c) 0.5

d) 0.2

View Answer

Explanation: The constant ‘a’ for a tapered transmission line is given by L-1 ln(ZL/Z0). ‘a’ is a function of the tapered length, load and characteristic impedance. Substituting the given values in the above expression, ‘a’ has the value 0.1386.

6. Reflection co-efficient magnitude response is an exponential curve for tapered line.

a) True

b) False

View Answer

Explanation: The reflection co-efficient magnitude response of a exponential tapered line resembles only positive valued sinc function or can be called as a function with multiple peaks.

7. Triangular taper is the best solution for any impedance matching requirement.

a) True

b) False

View Answer

Explanation: Klopfenstein taper is the best and most optimized solution for impedance matching because reflection co-efficient has minimum value in the passband.

8. The maximum passband ripple in a Klopfenstein taper matching section is:

a) Г_{0}/cos h A

b) Г_{0}/sin h A

c) Г_{0}/ tan h A

d) None of the mentioned

View Answer

Explanation: The maximum passband ripple in a Klopfenstein taper matching section is Г

_{0}/cos h A. Here, Г

_{0}is the reflection co-efficient at zero frequency. A is a trigonometric function relating reflection co-efficient at zero frequency and maximum ripple in the passband.

9. For any load impedance, perfect match can be obtained and the minimum reflection co-efficient achieved can be zero.

a) True

b) False

View Answer

Explanation: From Bode-Fano criterion, there is a theoretical limit on the minimum achievable reflection co-efficient for a given load impedance. Hence, perfect match cannot be obtained.

10. For a given load (a fixed RC product), a broader bandwidth can be achieved with a low reflection co-efficient in the passband.

a) True

b) False

View Answer

Explanation: Based on the theoretical results of Bode-Fano criterion, a broader bandwidth can be achieved only at the expense of a higher reflection coefficient in the passband.

11. A perfect match can be obtained in the passband for any impedance matching circuit around the center frequency for which it is defined.

a) True

b) False

View Answer

Explanation: The passband reflection co-efficient cannot be zero unless the bandwidth is zero. Thus a perfect match can be obtained only at a finite number of discrete frequencies.

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