# Multiple choice question for engineering

## Set 1

1. Quadrature hybrids are those couplers which are:

a) 3 dB couplers

b) Directional couplers

c) They have a 90^{0} phase difference between signals in through and coupled arms.

d) All of the mentioned

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2. Branch-line couplers are also popular as Quadrature hybrids.

a) True

b) False

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3. The S matrix of a Quadrature hybrid is of size 4×4 and the diagonal elements of a matched coupler are all:

a) 1

b) 0

c) Cannot be determined

d) None of the mentioned

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4. A branch-line coupler is an asymmetric coupler.

a) True

b) False

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5. Branch-line couplers are preferably made using waveguides so as to obtain high gain and simple construction.

a) True

b) False

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6. A 50 Ω branch-line Quadrature hybrid has to be designed to operate over a range of frequencies. The branch-line impedance of this coupler so designed is:

a) 70.7 Ω

b) 35.4 Ω

c) 50 Ω

d) 100 Ω

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7. The plot S11 v/s frequency for a branch-line coupler has a straight line characteristic for a wide range of frequency around the designed frequency range.

a) True

b) False

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8. The curve of S14 for a branch-line coupler is similar to that of the S11 curve of the branch-line coupler.

a) True

b) False

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9. S12 and S13 curves for branch-line couplers are almost a straight line parallel to X –axis. Both the curves are similar and follow same path.

a) True

b) False

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10. If the branch-line impedance of a coupler designed to operate at 1 GHz is 70.70 Ω, then the characteristic impedance of the material of the arms of the branch-line coupler is:

a) 70.7 Ω

b) 50 Ω

c) 100 Ω

d) None of the mentioned

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## Set 2

1. If a transmission line of characteristic impedance 50 Ω is to be matched to a load of 100Ω, then the characteristic impedance of the ƛ/4 transmission line to be used is:

a) 70.71 Ω

b) 50 Ω

c) 100 Ω

d) 75 Ω

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_{1}=√(ZₒR)L. substituting the given values, we get Z

_{1}=70.71 Ω.

2. If a λ/4 transmission line is 100Ω is used to match a transmission line to a load of 100Ω, then the characteristic impedance of the transmission line is:

a) 100 Ω

b) 50 Ω

c) 70.71 Ω

d) 200 Ω

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_{1}=√(ZₒR)L. substituting the given values, Z

_{0}=100 Ω.

3. Expression for the characteristic impedance of a transmission line(λ/4) used for impedance matching is:

a) Z_{1}=√(ZₒR)L

b) Z_{1}=√(Zₒ/R)L

c) Z_{1}=√(Zₒ+R)L

d) None of the mentioned

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_{1}=√(ZₒR)L.

4. If there is no standing wave on a transmission line, then the value of SWR is:

a) 1

b) 0

c) Infinity

d) Insufficient data

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5. When a λ/4 transmission line is used for impedance matching, then which of the following is valid?

a) Standing waves are present on the λ/4 transmission line

b) No standing waves on the λ/4 transmission line

c) Standing waves are not present both on the feed line and the matching λ/4 line

d) Standing waves are present on both the feed line and the matching λ/4 line

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6. For a transmission line , if the input impedance of the transmission line is 100Ω with a characteristic impedance of 150Ω, then the magnitude of the reflection co efficient:

a) 0.5

b) 1

c) 0.2

d) 0

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_{in}-Zₒ)/(Z

_{in}+ Zₒ). Substituting the given values in the above expression, reflection co-efficient is 0.2.

7. If the reflection co-efficient of a transmission line is 0.334 with a characteristic impedance of 50Ω then the input impedance of the transmission line is:

a) 100 Ω

b) 50 Ω

c) 150 Ω

d) None of the mentioned

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_{in}-Zₒ)/(Z

_{in}+ Zₒ). The input impedance of the transmission line is 100Ω

8. When a transmission line of characteristic impedance(50Ω) zₒ is matched to a load by a λ/4 transmission line of characteristic impedance 100Ω, then the transmission co efficient is:

a) 1.5

b) 0.5

c) 1.333

d) 2

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_{1}of the line is obtained using the expression 2Z

_{1}/ (Z

_{1}+Z

_{0}). Here Z

_{1}is the characteristic impedance of the λ/4 transmission line and Z

_{1}is the characteristic impedance of the transmission line. Substituting the given values, we get T

_{1}=1.3333.

9. If a transmission line of zₒ=50Ω is matched using λ/4 transmission line of z₁=100Ω, then the transmission co efficient T₂ is:

a) 1

b) 0.6667

c) 1.3333

d) 2

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_{2}of the line is obtained using the expression 2Z

_{0}/ (Z

_{1}+Z

_{0}). Here Z

_{1}is the characteristic impedance of the λ/4 transmission line and Z

_{0}is the characteristic impedance of the transmission line. Substituting the given values, we get T

_{2}=0.6667.

10. If the transmission co-efficient T₁ of a transmission line is 1.333 and the characteristic impedance of the λ/4 transmission line used is 100Ω, then the characteristic impedance of the transmission line is:

a) 50Ω

b) 100Ω

c) 70.71Ω

d) None of the mentioned

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_{1}/ (Z

_{1}+Z

_{0}). Substituting the known values, the characteristic impedance of the transmission line is 50Ω.

## Set 3

1. A quarter wave transformer is useful for matching any load impedance to a transmission line.

a) True

b) False

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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

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3. If a narrow band impedance match is required, then more multi section transformers must be used.

a) True

b) False

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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

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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

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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

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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

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8. Quarter wave transformers cannot be used for non-TEM lines for impedance matching.

a) True

b) False

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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

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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

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## Set 4

1. The modes of propagation supported by a rectangular wave guide is:

a) TM, TEM, TE modes

b) TM, TE

c) TM, TEM

d) TE, TEM

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2. A hollow rectangular waveguide cannot propagate TEM waves because:

a) Of the existence of only one conductor

b) Of the losses caused

c) It is dependent on the type of the material used

d) None of the mentioned

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3. For any mode of propagation in a rectangular waveguide, propagation occurs:

a) Above the cut off frequency

b) Below the cut off frequency

c) Only at the cut-off frequency

d) Depends on the dimension of the waveguide

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4. In TE mode of wave propagation in a rectangular waveguide, what is the equation that has to be satisfied?

a) (∂^{2}/ ∂x^{2} + ∂^{2}/ ∂y^{2}+ kC^{2}).HZ(x, y) =0

b) (∂^{2}/ ∂x^{2} + ∂^{2}/ ∂y^{2}– kC^{2}).HZ(x, y) =0

c) (∂^{2}/ ∂x^{2} – ∂^{2}/ ∂y^{2}+ kC^{2}).HZ(x, y) =0

d) None of the mentioned

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5. Dominant mode is defined as:

a) Mode with the lowest cut off frequency

b) Mode with the highest cut off frequency

c) Any TEM mode is called a dominant mode

d) None of the mentioned

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6. For TE1ₒ mode, if the waveguide is filled with air and the broader dimension of the waveguide is 2 cm, then the cutoff frequency is:

a) 5 MHz

b) 7.5 MHz

c) 7.5 GHz

d) 5 GHz

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7. TEₒₒ mode for a rectangular waveguide:

a) Exists

b) Exists but defined only under special cases

c) Does not exist

d) Cannot be determined

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8. For dominant mode propagation in TE mode, if the rectangular waveguide has a broader dimension of 31.14 mm , then the cutoff wave number:

a) 100

b) 500

c) 50

d) 1000

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9. The lowest mode of TM wave propagation is:

a) TM10 mode

b) TM01 mode

c) TM11 mode

d) TM12 mode

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10. The cutoff frequency for the dominant mode in TM mode propagation for a rectangular waveguide of dimension of 30mm*40mm is:

a) 2 GHz

b) 1 GHz

c) 2 MHz

d) 4 MHz

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^{2}+ (π/b)

^{2}). Here, ‘a’ and ‘b’ are the dimensions of the waveguide. Substituting the corresponding values, the cutoff frequency is 2 GHz.

11. In TE10 mode of wave propagation in a rectangular waveguide, if the broader dimension of the waveguide is 40 cm, then the cutoff wavelength for that mode is:

a) 8 cm

b) 6 cm

c) 4 cm

d) 2 cm

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12. In TE01 mode of wave propagation in a rectangular waveguide, if the smaller dimension of the waveguide is 2 cm, then the cutoff wavelength for that mode is:

a) 4 cm

b) 8 cm

c) 1 cm

d) 2 cm

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## Set 5

1. Discontinuities in the matching quarter wave transformer are not of considerable amount and are negligible.

a) True

b) False

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2. The overall reflection coefficient of a matching quarter wave transformer cannot be calculated because of physical constraints.

a) True

b) False

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3. In the multiple reflections analysis method, the total reflection is:

a) An infinite sum of partial reflections

b) An infinite sum of partial reflection and transmissions

c) Constant value

d) Finite sum of partial reflections

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4. The expression for total reflection in the simplified form is given by:

a) Г=Г_{1}+ Г_{3}e^{-2jθ}

b) Г=Г1_{1}+Г_{3}

c) Г=Г_{12}+ Г_{3}e^{-2jθ}

d) Г= Г_{1}+ Г_{2}e^{-2jθ}

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_{1}), and the first reflection from the discontinuity between Z2 and ZL (Г

_{3}e

^{-2jθ}).

5. The e^{-2jθ} term in the expression for total reflection in a single section quarter wave transformer impedance matching network Г=Г_{1}+ Г_{3}e^{-2jθ} signifies:

a) Phase delay

b) Frequency change

c) Narrowing bandwidth

d) None of the mentioned

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^{-2jθ}in Г=Г

_{1}+ Г

_{3}e

^{-2jθ}accounts for phase delay when the incident wave travels up and down the line. This factor is a result of multiple reflections.

6. If the first and the third reflection coefficients of a matched line is 0.2 and 0.01, then the total reflection coefficient if quarter wave transformer is used for impedance matching is:

a) 0.2

b) 0.01

c) 0.21

d) 0.19

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_{1}+ Г

_{3}e

^{-2jθ}. Given that Г

_{1}=0.2 and Г

_{3}=0.01, β=2π/λ, l=λ/4. θ=βl, Substituting the given values in the above 2 given equations, the total reflection coefficient is 0.19.

7. If a λ/4 transmission line is used for impedance matching, then always Г_{1}> Г_{3}.

a) True

b) False

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_{3}). Г

_{1}is the reflection from the junction of the transmission line and the λ/4 matching section. Since this end will have some improper matching and discontinuities, Г

_{1}is always greater than Г

_{3}.

8. To compute the total reflection of a multi-section transmission line, the lengths of the transmission lines considered are all unequal.

a) True

b) False

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9. If Z_{L}< Z_{0}, then the reflection coefficient at that junction is:

a) Г_{N}<0

b) Г_{N}>0

c) Г_{N}>1

d) None of the mentioned

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_{L}< Z

_{0}, then the reflection coefficient at that junction is always negative. That is, Г

_{N}<0.

10. The total approximate reflection coefficient is a finite sum of reflection co-efficient of individual matching section of the matching network.

a) True

b) False

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_{N}, then the total reflection is the sum of reflections that occur due to individual sections. There is an exponential component associated with each reflection coefficient that decays exponentially.

11. Using the relation for total reflection co-efficient certain designs of matching networks can be made as per practical requirements.

a) True

b) False

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_{N}and using enough sections (N).