# Multiple choice question for engineering

## Set 1

1. The key difference between circuit theory and transmission line theory is:

a) circuit elements

b) voltage

c) current

d) electrical size

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2. Transmission line is a _________ parameter network.

a) lumped

b) distributed

c) active

d) none of the mentioned

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3. For transverse electromagnetic wave propagation, we need a minimum of:

a) 1 conductor

b) 2 conductors

c) 3 conductors

d) bunch of conductors

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4. To model a transmission line of infinitesimal length Δz, the lumped element that is not used is:

a) resistor

b) inductor

c) capacitor

d) transistor

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5. _________ and __________ contribute to the impedance of a transmission line in the lumped element representation.

a) resistor, inductor

b) resistor, capacitor

c) capacitor, inductor

d) transistor, capacitor

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6. _________ and __________ contribute to the admittance of a transmission line in the lumped element representation.

a) conductance G, capacitor

b) conductance, inductor

c) resistor, capacitor

d) resistor, inductor

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7. Characteristic impedance of a transmission line is:

a) impedance Z of a transmission line

b) impedance which is a constant at any point on the transmission line

c) reciprocal of admittance of a transmission line

d) none of the mentioned

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8. Propagation constant γ is a :

a) real value

b) none of the mentioned

c) imaginary value

d) complex value

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9. Attenuation constant α signifies:

a) real part of propagation constant

b) loss that the transmission line causes

c) none of the mentioned

d) all of the mentioned

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10. Propagation constant γ is given by:

a) α+jβ

b) α-jβ

c) α/jβ

d) α.jβ

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11. Characteristic impedance Zₒ is given by:

a) √Z/Y

b) √ZY

c) √Z+√Y

d) √Z-√Y

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12. Propagation constant γ in terms of admittance and impedance of the transmission line is:

a) √Z/Y

b) √ZY

c) ZY

d) ZY*

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## Set 2

1. Expression for input impedance of a transmission line in terms of load impedance and characteristic impedance is:

a) Z_{0} (Z_{L}+j Z_{0}tan βl)/ (Z_{0}+j Z_{L}tan βl)

b) (Z_{0}+j Z_{L}tan βl)/ (Z_{L}+j Z_{0}tan βl)

c) Z_{0} (Z_{L}-j Z_{0}tan βl)/ (Z_{0}-j Z_{L}tan βl)

d) (Z_{0}-j Z_{L}tan βl)/ (Z_{L}-j Z_{0}tan βl)

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_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan βl).

2. Input impedance of a short circuited transmission line is :

a) -jZ_{0}tanβl

b) jZ_{0}tanβl

c) jZ_{0}cotβl

d) – jZ_{0}cotβl

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_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan βl), input impedance of the transmission line comes out to be jZ

_{0}tanβl.

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

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_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan 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

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_{0}tanβl.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) -jZ_{0}tanβl

b) jZ_{0}tanβl

c) jZ_{0}cotβl

d) -jZ_{0}cotβl

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_{L}=0) in the expression for input impedance of a transmission line Z

_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan βl), input impedance of the open circuited transmission line comes out to be- jZ

_{0}cotβl.

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

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_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan 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

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_{0}(Z

_{L}+j Z

_{0}tan βl)/ (Z

_{0}+j Z

_{L}tan 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

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_{0}cotβl. 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}+Z_{0})

b) (Z_{L}-Z_{0})/ (Z_{L}+Z_{0})

c) 2Z_{0}/( Z_{L}+Z_{0})

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

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_{L}-Z

_{0})/ (Z

_{L}+Z

_{0}) in the equation for transmission co-efficient, we get 2Z

_{L}/ ( Z

_{L}+Z

_{0}).

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

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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

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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

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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

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^{2}dB. Substituting e=2.718 in the above equation , 1Np=8.686 dB.

## Set 3

1. A T junction power divider can be used only for division of power.

a) True

b) False

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2. The lossless T junction dividers can be can all be modeled as a junction of three transmission lines.

a) True

b) False

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3. For the realization of lossless T-junction power divider using transmission lines, the characteristic impedance of the transmission line has to be real.

a) True

b) False

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4. The output power measured at the 2 ports of the T junction:

a) Is a constant

b) Variable

c) Is not real power

d) None of the mentioned

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5. Hybrid couplers are also a type of directional couplers.

a) True

b) False

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6. If the input power is divided in the ratio of 2:1 in a T- junction coupler and the characteristic impedance of the 2 output lines is 150Ω and 75Ω, then the impedance of the input line is:

a) 100Ω

b) 50Ω

c) 150Ω

d) None of the mentioned

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7. A lossy T junction can be matched at all the three ports.

a) True

b) False

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8. The diagonal elements of the s matrix of a resistive T junction are:

a) 0

b) 1

c) 0.5

d) 1.5

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9. The power delivered to the input port of a resistive power divider is equal to the source voltage applied.

a) True

b) False

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10. The power input at the port 1 of resistive T junction is equally divided among the 2 output ports of the T junction.

a) True

b) False

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## Set 4

1. As the beam area of an antenna decreases, the directivity of the antenna:

a) Increases

b) Decreases

c) Remains unchanged

d) Depends on the type of the antenna

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2. If an antenna radiates over half a sphere, directivity of the antenna is:

a) Two

b) Four

c) Three

d) One

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3. The half power beam width of an antenna in both θ and φ are 400 each. Then the gain of the antenna is:

a) 23

b) 25

c) 14

d) 27

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4. The number N of radio transmitters or point sources of radiation distributed uniformly over the sky which an antenna can resolve is given by:

a) 4π/ ΩA

b) 2π/ ΩA

c) π/ ΩA

d) None of the mentioned

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5. Ideally, the number of point sources an antenna can resolve is numerically equal to:

a) Gain of the antenna

b) Directivity

c) Beam efficiency

d) Beam area

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6. Effective aperture is a parameter of the antenna that gives the physical aperture of the antenna.

a) True

b) False

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7. Effective aperture in terms of beam area and operating wavelength is given by the relation:

a) λ^{2}/ ΩA

b) ΩA / λ^{2}

c) λ^{2}× ΩA

d) No such relationship exists

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^{2}/ ΩA. Here ΩA is the beam area. If the beam area is specified in terms of the operating wavelength λ, then effective are of the antenna can be made operating wavelength independent.

8.________ of an antenna is defined as the ratio of the induced voltage to the incident electric field.

a) Effective height

b) Gain

c) Directivity

d) Loss

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9. The directivity of an antenna in terms of the aperture efficiency and operating wavelength is given by:

a) 4πAe/λ^{2}

b) 2πAe/λ^{2}

c) πAe/λ^{2}

d) None of the mentioned

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^{2}. Here Ae is the aperture efficiency. λ is the operating frequency. With an increase in the effective aperture area of an antenna, directivity of the antenna can be increased making the radiated beam narrower.

10. A radio link has 15 W transmitter connected to an antenna of 2.5 m^{2} effective aperture at 5 GHz. The receiving antenna has an effective aperture of 0.5 m^{2} and is located at a 15 Km line of sight distance from transmitting antenna. Assuming lossless, matched antennas, the power delivered to the receiver is:

a) 20 µW

b) 15 µm

c) 23 µm

d) 25 µm

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^{2}λ

^{2}). Substituting the given values in the above equation, the power at the receiver is 23 µm.

## Set 5

1. A practical oscillator has a frequency spectrum consisting of a single delta function at its operating frequency.

a) True

b) False

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2. ____________ due to random fluctuations caused by thermal and other noise sources appear as broad continuous distribution localized about the output signal.

a) Phase noise

b) White noise

c) Thermal noise

d) Shot noise

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_{m}. phase noise due to random fluctuations caused by thermal and other noise sources appear as broad continuous distribution localized about the output signal.

3. The phase variation for an oscillator or synthesizer is given by:

a) ∆f*sin ω_{m}t/ f_{m}

b) ∆f / f_{m}

c) Sin ω_{m}t/ f_{m}

d) None of the mentioned

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_{m}t/ f

_{m}. here, f

_{m}is the modulating signals frequency, ∆f is the change in the frequency.

4. The expression for phase noise in an oscillator is given by:

a) θ_{rms}^{2}

b) θ_{rms}^{2}/√2

c) θ_{rms}^{2}/2

d) θ_{rms}^{2}/ 3

### View Answer

_{rms}

^{2}/2. θ

_{rms}is the rms value of the phase deviation. Phase noise is directly proportional to the square of the RMS value of the phase deviation. Greater the deviation, higher is the phase noise.

5. Phase noise at the output of an oscillator is given by:

a) kBFGT_{0}

b) kT_{0}F/Pc

c) kT_{0}F/Pc

d) None of the mentioned

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_{0}F/Pc. here k is the Boltzmann’s constant. B is the operating bandwidth of the system, here the equation is considered for a bandwidth of 1 Hz as per the definition of phase noise. F is the figure of merit of system.

6. Noise power versus frequency for an amplifier has spikes at the operating frequency without the application of an input voltage.

a) True

b) False

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7. An idealized power spectral density of amplifier has a straight line parallel to X axis and the noise is constant at all frequencies.

a) True

b) False

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8. At higher frequencies of operation of an oscillator, induced noise is mostly:

a) Thermal noise

b) White noise

c) Shot noise

d) Flicker noise

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9. A GSM cellular telephone standard requires a minimum of 9 dB rejection of interfering signal levels of -23 dBm at 3 MHz from the carrier, -33 dBm at 1.6 MHz from the carrier, and -43 dBm at 0.6 MHz from the carrier, for a carrier level of -99 dBm. Determine the required local oscillator phase noise at 3 MHz carrier frequency offset.

a) -138 dBc/Hz

b) -128 dBc/Hz

c) -118 dBc/Hz

d) None of the mentioned

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10. The most affected parameter of a receiver by the phase noise is signal to noise ratio.

a) True

b) False