# Multiple choice question for engineering

## Set 1

1. The matched network is placed between:

a) load and transmission line

b) source and the transmission line

c) source and the load

d) none of the mentioned

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2. When a transmission line is matched to a load using a matched network, reflected waves are present:

a) between the load and the matched network

b) between the matched network and the transmission line

c) between the source and the transmission line

d) between the matched network and source

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3. Impedance matching sensitive receiver components may improve the _____ of the system.

a) noise

b) SNR

c) amplification factor

d) thermal noise

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4. One of the most important factors to be considered in the selection of a particular matching network is:

a) noise component

b) amplification factor

c) bandwidth

d) none of the mentioned

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5. The simplest type of matching network, L section consists of _______ reactive elements.

a) one

b) two

c) four

d) six

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6. The major limitation of a lumped elements matching ‘L’ network is:

a) they are not equally efficient at higher frequencies as they are at lower frequencies.

b) size of the network

c) they restrict flow of current

d) none of the mentioned

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7. An ‘L’ network is required to match a load impedance of 40Ω to a transmission line of characteristic impedance 60Ω. The components of the L network are:

a) 28.28+j0 Ω

b) 28.28+j1 Ω

c) 50Ω

d) 48.9Ω

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_{L}(Z

_{0}– R

_{L}))-X

_{L}. Substituting the values given, the matching network impedance is 28.28Ω.

8. The imaginary part of the matching network is given by the relation:

a) ±(√(Z_{0}– R_{L})/R_{L})Z0_{0}

b) ±(√(Z_{0}– R_{L})/R_{L})

c) ±(√(Z_{0}– R_{L})/ Z_{0}

d) None of the mentioned

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_{0}– R

_{L})/R

_{L})Z

_{0}.

9. Which of the following material is not used in the fabrication of resistors of thin films?

a) nichrome

b) tantalum nitride

c) doped semiconductor

d) pure silicon

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10. Large values of inductance can be realized by:

a) loop of transmission line

b) spiral inductor

c) coils of wires

d) none of the mentioned

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11. A short transmission line stub can be used to provide a shunt capacitance of:

a) 0-0.1µF

b) 0-0.1pF

c) 0-0.1nF

d) 1-10pF

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## Set 2

1. Classical p-n junction diode cannot be used for high frequency applications because of:

a) High bias voltage

b) High junction capacitance

c) Frequency sensitive

d) High forward biased current

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2. Schottky barrier diode is a sophisticated version of the point contact ______________

a) Germanium diode

b) Silicon crystal diode

c) GaAs diode

d) None of the mentioned

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3. Advantage of Schottky diode over silicon crystal diode is the presence minority charge carriers.

a) True

b) False

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4. As the area of rectifying contact goes on increasing, the forward resistance of the Schottky diode:

a) Increases

b) Decreases

c) Remains unchanged

d) None of the mentioned

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5. The number of semiconductor layers in a TRAPATT diode is:

a) Two

b) Three

c) Four

d) One

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6. In order to achieve high current density, a compromise in _______is made in a TRAPATT diode.

a) Gain

b) Size

c) Operating frequency

d) No compromise is made on any of the parameter

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7. TRAPATT diode is normally mounted at a point inside a coaxial resonator where there is minimum RF voltage swing.

a) True

b) False

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8. A major disadvantage of TRAPATT diode is:

a) Fabrication is costly

b) Low operational bandwidth

c) Low gain

d) High noise figure

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9. _________ gives a frequency domain representation of a signal, displaying the average power density versus frequency.

a) CRO

b) Oscilloscope

c) Spectrum analyzer

d) Network analyzer

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10. The most important functional unit of a spectrum analyzer is:

a) Mixer

b) IF amplifier

c) Sensitive receiver

d) None of the mentioned

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11. A tunnel diode is a p-n junction diode with a doping profile that allows electron tunneling through a narrow energy band gap.

a) True

b) False

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## Set 3

1. Microwave resonators can be constructed from open sections of waveguide.

a) True

b) False

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2. There is no energy stored inside a rectangular waveguide cavity resonator.

a) True

b) False

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3. A rectangular cavity supports:

a) TEM mode of resonance

b) TM mode of resonance

c) TE mode of resonance

d) TE, TM modes of resonance

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4. A waveguide is open circuited at both the ends to use it as a waveguide resonator.

a) True

b) False

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5. In order to obtain the resonant frequency of a rectangular waveguide, the closed cavity has to satisfy:

a) Gaussian equation

b) Helmholtz equation

c) Ampere’s law

d) None of the mentioned

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6. Given the dimension of the waveguide as b<a<d, no resonant mode exists for this specification of dimensions.

a) True

b) False

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7. Unloaded Q of a rectangular waveguide cavity resonator:

a) Does not exist

b) Defined as the ratio of length of the waveguide to breadth of the waveguide

c) Defined as the ratio of stored energy to the power dissipated in the walls

d) None of the mentioned

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8. Find the wave number of a rectangular cavity resonator filled with a dielectric of 2.25 and designed to operate at a frequency of 5 GHz.

a) 157.08

b) 145.2

c) 345.1

d) 415.08

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9. The required length of the cavity resonator for l=1 mode (m=1, n=0) given that the wave number of the cavity resonator is 157.01 and the broader dimension of the waveguide is 4.755 cm:

a) 1.10 cm

b) 2.20 cm

c) 2.8 cm

d) 1.8 cm

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^{2}. Substituting the given values in the equation, the required length of the waveguide is 2.20 cm.

10. If the loss tangent of a rectangular waveguide is 0.0004, then Q due to dielectric loss is:

a) 1250

b) 2450

c) 2500

d) 1800

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## Set 4

1. Power dividers and couplers are ______ microwave components used for power division or power combining.

a) Passive

b) Active

c) Linear

d) Non linear

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2. T- junction is an example for:

a) 2 port network

b) 3 port network

c) 4 port network

d) None of the mentioned

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3. A T junction has a 3×3 ‘s’ matrix.

a) True

b) False

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4. If a device is passive and contains no anisotropic elements, then the device is_______ network.

a) Reciprocal

b) Non reciprocal

c) Lossless

d) Lossy

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5. Scattering matrix of a reciprocal network is:

a) Symmetric

b) Asymmetric

c) Identity matrix

d) Null matrix

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6. If all the ports of a microwave network are matched, then the diagonal elements of the S matrix of the network is zero.

a) True

b) False

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7. If a microwave network is lossless, then S matrix of the microwave network is:

a) Unitary

b) Symmetric

c) Identity matrix

d) Zero matrix

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^{2}+│S13│

^{2}= 1. This condition has to be satisfied for a 3 port network. This can be generalized for any n port network.

8. A lossless reciprocal 3 port network can be matched at all the three ports.

a) True

b) False

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9. A circulator is a 3 port network that allows energy flow in clockwise direction only.

a) True

b) False

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10. The diagonal elements of the S matrix of an improperly matched circulator is zero.

a) True

b) False

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11. Coupling factor of a directional coupler must be maximum and is a key factor that determines the performance of the coupler.

a) True

b) False

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12. Directivity of a directional coupler signifies the direction of power flow in the coupler.

a) True

b) False

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13. Isolation of a directional coupler is a measure of the:

a) Power delivered to the uncoupled port

b) Power delivered to the coupled port

c) Power delivered to the second port

d) None of the mentioned

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14. Insertion loss is the power delivered to the through port.

a) True

b) False

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15. In a symmetric coupler, the power delivered to the through port and output port are equal.

a) True

b) False

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^{0}.

## Set 5

1. The passband response of a binomial matching transformer can be called optimum:

a) if the roll off in the response curve is high

b) if the response is flat in the impedance matched region

c) if the matching network is frequency sensitive

d) none of the mentioned

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2. If a quality binomial matching transformer gives a good flat response curve, it is called “maximally flat”.

a) true

b) false

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3. The response curve of a binomial matching transformer is plotted for each section of the matching network individually and then analyzed for optimum solution.

a) true

b) false

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4. To obtain a flat curve in the response of a binomial multisection transformer, N-1 derivatives of │Г (θ) │are set to zero. This implies:

a) the frequency sensitivity of the matching section is increased linearly

b) the frequency sensitivity of the matching section is increased exponentially

c) roll off in the curve is increased

d) none of the mentioned

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5. The condition │Г (θ) │=0 for θ=π/2 of a binomial multi section transformer corresponds to the:

a) upper cutoff frequency

b) lower cutoff frequency

c) center frequency

d) none of the mentioned

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6. The reflection co-efficient magnitude of a binomial multisection transformer is:

a) 2^{N}│A││cos (θ)│^{N}

b) 2^{N}│A│

c) 2^{N}│cos (θ) │^{N}

d) none of the mentioned

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^{-N}(Z

_{L}– Z

_{0})/ (Z

_{L}+ Z

_{0}).

7. The reflection coefficient Г_{N} in terms of successive impedances Z_{n} and Z_{n+1} when multisection transformers are used in a binomial matching transformer is given by:

a) 0.5ln (Z_{n+1}/Z_{n})

b) ln (Z_{n+1}/Z_{n})

c) 0.5ln (Z_{n}/Z_{n+1})

d) (Z_{n}/Z_{n+1})

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_{n+1}/Z

_{n}).

8. In the plot of normalized frequency v/s reflection co-efficient for a binomial multisection filter, the curve has a dip at:

a) center frequency

b) upper cutoff frequency

c) lower cutoff frequency

d) none of the mentioned

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9. As the number of sections in the binomial multisection transformer increases the plot of normalized frequency v/s reflection co-efficient has a wider open curve.

a) true

b) false

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10. A three section binomial transformer is used to match a 100Ω transmission line to a 50Ω transmission line. Then the value of the constant ‘A’ for this design is:

a) -0.0433

b) 0.0433

c) 0.01

d) -0.01

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^{-(n+1)}ln (Z

_{L}/Z

_{0}), Where N is the number of sections in the matching network. Substituting the given values in the equation for ‘A’, the value of A is -0.0433.