# Multiple choice question for engineering

## Set 1

1. ______ is a device that produces a phase shift of a required amount of the input wave.

a) Phase shifter

b) Attenuator

c) Resonator

d) None of the mentioned

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2. Phase shifters are used in _______ where the antenna beam can be steered in space by electronically controlled phase shifters.

a) Phased array antennas

b) Dipole array antennas

c) Slot antennas

d) Patch antennas

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3. Reciprocal phase shifters give different phase shift in different direction.

a) True

b) False

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4. If a ferrite slab provides a phase shift of 48⁰/ cm, then the length of the ferrite slab required to produce a phase shift of 180⁰ is:

a) 4 cm

b) 3.75 cm

c) 4.5 cm

d) 3.5 cm

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5. If a ferrite slab provides a phase shift of 48⁰/ cm, then the length of the ferrite slab required to produce a phase shift of 90⁰ is:

a) 2.44 cm

b) 1.88 cm

c) 4.5 cm

d) 3.5 cm

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6. Gyrator is a device that produces a phase shift of ____ between the input and output.

a) 90⁰

b) 180⁰

c) 45⁰

d) None of the mentioned

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7. The scattering matrix of a gyrator is:

a) Symmetric

b) Skew symmetric

c) Identity matrix

d) Null matrix

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8. Ferrite phase shifters have more advantages over FETs and diodes in using them in microwave integrated circuits.

a) True

b) False

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9. A gyrator can be made a passive device by certain design methods so that they do not affect the power levels of the circuit in which they are used.

a) True

b) False

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10. If a ferrite slab produces a phase shift of 0.836 rad/ cm, then the length of the slab required to produce a phase shift of 135⁰ is:

a) 2.81 cm

b) 3 cm

c) 2 cm

d) 3.4 cm

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## Set 2

1. Field effect transistors are different from BJTs in that they are _________

a) monopolar devices

b) bipolar devices

c) bidirectional device

d) none of the mentioned

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2. GaAs MESFET –metal semiconductor field effect transistor are one of the widely used categories of FETs.

a) true

b) false

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3. At frequencies above 10GHz, MESFET are not suitable for microwave applications due to parasitic effects.

a) true

b) false

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4. Advantage of using GaAs in MESFET as compared to use of silicon is:

a) GaAs are cost effective

b) they have higher mobility

c) they have high resistance for flow of current in the reverse direction

d) none of the mentioned

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5. In MESFET, an applied signal at the gate modulates the electron carriers; this produces _______ in the FET.

a) voltage amplification

b) voltage attenuation

c) electron multiplication

d) electron recombination

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6. The frequency of operation of an FET is limited by:

a) drain to source voltage

b) gate to source voltage

c) gate length

d) effective area of an FET

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7. The S_{21} parameter for a MESFET is lesser than 1.

a) true

b) false

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_{21}parameter of the transistor was found to be greater than one under normal operating conditions. Here port 1 is at the gate and port 2 is at the drain.

8. The expression for short circuit current gain of an FET is given by:

a) g_{m}/ ωC_{gs}

b) I_{g}/g_{m}V_{c}

c) ωC_{gs}/ g_{m}

d) none of the mentioned

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_{D}/I

_{G}. This ratio in simplified form is given as g

_{m}/ ωC

_{gs}.

9. The upper threshold frequency of an FET, where short circuit gain is unity is given by:

a) g_{m}/2πC_{gs}

b) g_{m}/C_{gs}

c) g_{m}/ 2π

d) none of the mentioned

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_{m}, associated with the current generator of the small signal equivalent circuit. C

_{gs}is the capacitance measured between the gate and source terminals.

10. The scattering parameter S_{11} for an FET __________ with increase in the frequency of operation of the transistor.

a) increases

b) decreases

c) remains constant

d) none of the mentioned

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_{11}parameter of an FET decreases with the increase in the frequency of operation of an FET. The measured values are 0.97 at 1 GHz, and 0.49 at 12 GHz.

11. The curve of I_{DS} v/s V_{DS} of an FET does not vary with the gate to source voltage applied.

a) true

b) false

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_{DS}v/s V

_{DS}of an FET varies with the gate to source voltage applied. As the gate to source voltage applied becomes more positive, the drain to source current goes on increasing for an applied constant gate to source voltage.

12. High-power circuits generally use higher values of:

a) gate to source current

b) drain to source current

c) drain current

d) gate to source voltage

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13. High drain current at RF levels is achieved with the biasing and decoupling circuitry for a dual polarity supply.

a) true

b) false

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## Set 3

1. In a two wire transmission line, if the distance between the lines is 20 mm and the radii is 5 mm then the inductance of the line is:

a) 0.1 µH

b) 0.526 µH

c) 0.9 µH

d) 1 µH

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2. In a two wire transmission line , if the distance between the lines is 60mm and the radii is 10 mm , then the capacitive reactance of the line when operated at 12.5 GHz is

a) 20 pF

b) 21.13 pF

c) 23 pF

d) 12 pF

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^{-1}(D/2a). substituting the given values in the above expression, the capacitive reactance is 21.13 pF.

3. For a parallel plate type of a transmission line, then expression for conductance of the line is:

a) ∈(ω)w/d

b) 2R_{x}/x

c) μ/2π ln(w/d)

d) μ/π cosh^{-1}(w/2d)

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4. One of the Maxwell‘s curl equation that is satisfied inside a coaxial line is:

a) ∇×E =-jωµ (vector H)

b) ∇×E =-jωμ(vector E)

c) ∇×H=-jωμ(vector H)

d) ∇×H=jωμ(vector H)

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5. The wave impedance of air for a wave propagating in it is:

a) 377 Ω

b) 345 Ω

c) Insufficient data

d) None of the mentioned

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6. Wave impedance of a wave travelling in a medium of a relative permittivity 2 and permeability 4 is

a) 188.5 Ω

b) 200 Ω

c) 300 Ω

d) None of the mentioned

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7. For a parallel plate transmission line, if w= 12 mm and the distance between the plates is 2 mm, then the inductance of the transmission line is:

a) 0.2 µH

b) 0.1 µH

c) 0.3 µH

d) 0.4 µH

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8. Expression for capacitance of a two wire transmission line is

a) ∈’*π/cosh^{-1}(D/2a)

b) μ/π*cosh^{-1}(D/2a)

c) 2π∈/ln(D/2a)

d) ∈”*πω/cosh^{-1}(D/2a)

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^{-1}(D/2a). Capacitance of a two wire transmission line is dependent on the distance between the two lines and the radius of the line.

9. If the distance between the 2 wires in a 2 wire transmission line is 10 mm and the radii 2 mm, then the inductance of the transmission line is:

a) 0.62 µH

b) 1 µH

c) 2 µH

d) None of the mentioned

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^{-1}(D/2a)/π. Substituting the given values in the above expression, the inductance is 0.62 µH.

10. For a parallel plate transmission line, if the complex part of permittivity is 2.5, if the width is 100 mm and the distance between the plates is 10 mm, then the conductance of the transmission line is:

a) 25 Ʊ

b) 30 Ʊ

c) 45 Ʊ

d) None of the mentioned

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11. For a parallel plate transmission line, if the series resistance is 10 mΩ/m, and the width is 100 mm, then the resistance of the transmission line is:

a) 0.2 Ω

b) 1 Ω

c) 2 Ω

d) 5 Ω

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_{S}/W. substituting the given values in the above expression, the series resistance is 0.2 Ω.

## Set 4

1. Oscillators operating at millimeter wavelength are difficult to realize and are also less efficient.

a) true

b) false

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2. __________ is an example for a frequency multiplier.

a) resistor

b) inductor

c) capacitor

d) transistor

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3. The major drawback of frequency multipliers is that they have:

a) higher attenuation

b) complex construction methods

c) complex design

d) none of the mentioned

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4. A reactive diode multiplier uses _______ as the key electronic component for frequency multiplication.

a) zener diode

b) light emitting diode

c) varactor diode

d) Gunn diode

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5. A major disadvantage of frequency multipliers is that they multiply the noise factor along with frequency.

a) true

b) false

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6. If a frequency multiplier has a multiplication factor of 10, then the increase in noise level due to frequency multiplication is:

a) 10 dB

b) 20 dB

c) 25 db

d) 15 dB

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7. In a diode frequency multiplier, an input signal of frequency f_{o} applied to the diode is terminated with_________ at all frequencies other than required harmonic.

a) real impedances

b) reactive impedance

c) complex impedance

d) none of the mentioned

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_{o}applied to the diode is terminated with reactive impedance at all frequencies other than required harmonic nf

_{o}. if the diode junction capacitance has a square –law I-V characteristic , it is necessary to terminate unwanted harmonics with short circuit.

8. Resistive multipliers are more efficient as compared to reactive multipliers.

a) true

b) false

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9. Reactive multipliers have a disadvantage that they cannot be used at very high frequencies and they become less efficient.

a) true

b) false

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10. For a resistive frequency multiplier of multiplication factor 2, the maximum theoretical conversion efficiency is:

a) 50 %

b) 25 %

c) 75 %

d) 12.5 %

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^{2}where m is the multiplication factor. For a factor 2 multiplier, maximum theoretical conversion efficiency is 25 %.

## Set 5

1. Surface waves are typical by a field that decays ______away from the dielectric surface, with most of the field contained in or near the dielectric.

a) Linearly

b) Exponentially

c) Cubical

d) Field remains a constant

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2. Because of the presence of the dielectric, the phase velocity of a surface wave is:

a) Greater than that in vacuum

b) Lesser than that in vacuum

c) Independent of the presence of dielectric

d) Insufficient data

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3. For wave propagation on grounded dielectric sheet, the equation to be satisfied by Ez , in the region of presence of dielectric 0≤x≤d for the propagation to be in Z direction

a) (∂^{2}/∂x^{2} + ∈_{r}k_{0}^{2}– β^{2}) e^{Z(x,y)}=0

b) (∂^{2}/∂x^{2} + k_{0}^{2}– β^{2}) e^{Z(x,y)}=0

c) (∂^{2}/∂x^{2} – k_{0}^{2}+β^{2}) e^{Z(x,y)}=0

d) (∂^{2}/∂x^{2} + ∈_{r}k_{0}^{2}) e^{Z(x,y)}=0

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4. The cut off wavenumber for the region of dielectric in a grounded dielectric sheet is:

a) kC^{2}= ∈_{r}k_{0}^{2}-β^{2}

b) kC^{2}= ∈_{r}k_{0}^{2}+β^{2}

c) h^{2}= -k_{0}^{2}+β^{2}

d) kC^{2}= k^{2} + β^{2}

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^{2}= ∈

_{r}k

_{0}

^{2}-β

^{2}gives the cutoff wave number for the propagation of waves on a grounded dielectric sheet.

5. For surface waves on a dielectric sheet the cutoff frequency of the TM mode can be given as:

a) f_{C} = nC/2d√(ϵr-1)

b) f_{C} = C/2nd√(ϵr-1)

c) f_{C} = C/2nd√ϵr

d) f_{C} = 2C/nd√ϵr

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_{C}= nC/2d√(ϵr-1).

6. The cutoff frequency in TM1 mode for the propagation of EM waves on dielectric slab of relative permittivity 2.6 and thickness 20 mm is:

a) 6.5 GHz

b) 5.92 GHz

c) 4 GHz

d) 2 GHz

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_{C}= nC/2d√(ϵr-1).here n represents the mode. Substituting the given values, cutoff frequency is 5.92 GHz.

7. In TE of propagation, HZ must obey the below equation for wave propagation in the region of presence of dielectric:

a) (∂^{2}/∂x^{2} + kc^{2}) hZ(x,y)=0

b) (∂^{2}/∂x^{2}– h^{2})hZ(x,y)=0

c) (∂^{2}/∂x^{2} – Kc^{2})hZ(x,y)=0

d) (∂^{2}/∂x^{2} +h^{2})hZ(x,y)=0

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^{2}/∂x

^{2}+ kc

^{2}) hZ(x,y)=0

8. Cutoff frequency f_{C} for TEM mode of propagation is:

a) Fc= (2n-1)c/4d√εr -1

b) Fc= (2n-c)/2d(√εr-1)

c) Fc= (2n-1)/4d(√εr)

d) Fc= (2n-1)/8d√εr – 1

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9. What is the cutoff frequency of TE₁ mode of propagation if the relative permittivity of the slab is 3.2 and the thickness of the slab is 45 mm?

a) 2.24 GHz

b) 4 GHz

c) 1.12 GHz

d) 8 GHz

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10. The first propagating mode on a grounded dielectric is:

a) TMO mode

b) TM1 mode

c) TM2 mode

d) TM3 mode