Directions: The item consists of two statements, one labelled as the ‘Assertion (A)’ and the other as ‘Reason (R)’.You are to examine these two statements carefully and select the answers to the item using the codes given below:Assertion (A): A magnetron is not an amplifier, but an oscillator producing microwaves.Reason (R): In making their circular passes in the interaction space of a magnetron, the electrons excite the resonant cavities into oscillations.

Both A and R are individually true but R is not the correct explanation of A

Both A and R individually true and R is the correct explanation of A

Both A and R are individually true but R is not the correct explanation of A

Parallel resonant frequency of quartz crystal is given by:

1/ âˆš(lcâ‚’c/(câ‚’+c))

One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:

positive feedback is to be achieved

negative feedback is to be achieved

1800 phase shift is required between the transistor input and output.

Expression for over all noise figure of a mismatched amplifier is:

1+ (f-1)/ (1 -â”‚Ð“â”‚2)

(f-1)/ (1 -â”‚Ð“â”‚2)

Noise figure can be defined for any microwave network irrespective of any other constraints.

topic 5.6 low noise amplifier design

To flatten the gain response of a transistor:

biasing current has to be increased

input signal level has to increased

increase the operational bandwidth

give negative feedback to the amplifier

High gain is not achievable at microwave frequencies using BJT amplifiers because:

ports are not matched at high frequencies

characteristic impedance, first voltage minimum

characteristic impedance, first voltage maximum

217 + Mcqs in Antennas And Microwave Engineering in Electrical Engineering Page 2 McqOptions

51.	Directions: The item consists of two statements, one labelled as the ‘Assertion (A)’ and the other as ‘Reason (R)’.You are to examine these two statements carefully and select the answers to the item using the codes given below:Assertion (A): A magnetron is not an amplifier, but an oscillator producing microwaves.Reason (R): In making their circular passes in the interaction space of a magnetron, the electrons excite the resonant cavities into oscillations.
A.	Both A and R individually true and R is the correct explanation of A
B.	Both A and R are individually true but R is not the correct explanation of A
C.	A is true but R is false
D.	A is false but R is true
Answer» B. Both A and R are individually true but R is not the correct explanation of A

Discussion

52.	Match List-I with List-II and select the correct answer using the code given below the lists:List-I(Device)List-II(Application) a. Transferred electron devices i. Microwave amplifier b. Two-cavity Klystron ii. Microwave oscillator c. PIN diode iii. Microwave low power measurement d. Bolometer iv. Modulator
A.	a - iii, b - i, c - iv, d - ii
B.	a - ii, b - i, c - iv, d - iii
C.	a - iii, b - iv, c - i, d - ii
D.	a - ii, b - iv, c - i, d - iii
Answer» C. a - iii, b - iv, c - i, d - ii

Discussion

53.	A parabolic reflector used for reception with the direct broadcast system is 18 inches in diameter and operates at 12.4 GHz. The far-field distance for this antenna is:
A.	18 m
B.	13 m
C.	16.4 m
D.	17.3 m
Answer» E.

Discussion

54.	In transistor oscillators, FET and BJT are used. Instability is achieved by:
A.	giving a negative feedback
B.	giving a positive feedback
C.	using a tank circuit
D.	none of the mentioned
Answer» C. using a tank circuit

Discussion

55.	In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.
A.	true
B.	false
Answer» C.

Discussion

56.	To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.
A.	true
B.	false
Answer» C.

Discussion

57.	For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:
A.	Ð“in=Ð“l
B.	Ð“in=-Ð“l
C.	Ð“in=1/Ð“l
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

58.	In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.
A.	true
B.	false
Answer» C.

Discussion

59.	In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.
A.	true
B.	false
Answer» B. false

Discussion

60.	Any device with negative impedance as its characteristic property can be called:
A.	energy source
B.	energy sink
C.	oscillator
D.	none of the mentioned
Answer» B. energy sink

Discussion

61.	The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:
A.	3 mhz
B.	0.3 mhz
C.	6 mhz
D.	9 mhz
Answer» B. 0.3 mhz

Discussion

62.	Parallel resonant frequency of quartz crystal is given by:
A.	1/ âˆš(lcâ‚’c/(câ‚’+c))
B.	1/âˆšlc
C.	1/âˆšlcâ‚’
D.	1/ âˆš(l(câ‚’+c) )
Answer» B. 1/âˆšlc

Discussion

63.	In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:
A.	0.25 mhz
B.	2.5 mhz
C.	25 mhz
D.	5 mhz
Answer» B. 2.5 mhz

Discussion

64.	A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.
A.	true
B.	false
Answer» C.

Discussion

65.	In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.
A.	true
B.	false
Answer» C.

Discussion

66.	In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:
A.	capacitive
B.	inductive
C.	both capacitive and inductive
D.	none of the mentioned
Answer» C. both capacitive and inductive

Discussion

67.	Quartz crystal and tourmaline used in oscillators work on the principle of:
A.	photo electric effect
B.	piezo electric effect
C.	raman effect
D.	black body radiation
Answer» C. raman effect

Discussion

68.	One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:
A.	positive feedback is to be achieved
B.	negative feedback is to be achieved
C.	1800 phase shift is required between the transistor input and output.
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

69.	Expression for over all noise figure of a mismatched amplifier is:
A.	1+ (f-1)/ (1 -â”‚Ð“â”‚2)
B.	1
C.	1+ (f-1)
D.	(f-1)/ (1 -â”‚Ð“â”‚2)
Answer» B. 1

Discussion

70.	Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:
A.	t (2l-1)
B.	t (2l+1)
C.	t (2l*1)
D.	t / (2l-1)
Answer» B. t (2l+1)

Discussion

71.	For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:
A.	2l
B.	1/2l
C.	l
D.	1/l
Answer» C. l

Discussion

72.	Noise equivalent temperature of a 2 stage cascade network is given by:
A.	te1 + te2/ g1
B.	te1 + te1
C.	te1 / te1
D.	none of the mentioned
Answer» B. te1 + te1

Discussion

73.	Expression for noise of a two port network considering the noise due to transmission line and other lossy components is:
A.	gktb + gnadded
B.	gktb
C.	gnadded
D.	none of the mentioned
Answer» B. gktb

Discussion

74.	Noise figure can be defined for any microwave network irrespective of any other constraints.
A.	true
B.	false
C.	topic 5.6 low noise amplifier design
Answer» C. topic 5.6 low noise amplifier design

Discussion

75.	The equivalent noise temperature of a network given the noise figure of the network or system is:
A.	t0(f-1)
B.	t0(f+1)
C.	t0(f)
D.	t0/f
Answer» B. t0(f+1)

Discussion

76.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is defined as the ratio of desired signal power to undesired noise power.
A.	signal to noise ratio
B.	noise to signal ratio
C.	noise figure
D.	noise temperature
Answer» B. noise to signal ratio

Discussion

77.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is defined as the ratio of input signal to noise ratio to the output signal to noise ratio.
A.	noise figure
B.	noise temperature
C.	snro
D.	none of the mentioned
Answer» B. noise temperature

Discussion

78.	Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:
A.	50.4 khz
B.	35.1 khz
C.	45.9 khz
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

79.	Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:
A.	19.89 khz
B.	25 khz
C.	45 khz
D.	12 khz
Answer» B. 25 khz

Discussion

80.	Amplifier efficiency is the ratio of RF output power to DC input power. This parameter determines the performance of an amplifier.
A.	true
B.	false
Answer» B. false

Discussion

81.	For Colpitts oscillator, the capacitors C1 and C2 in the feedback network are 1 ÂµF and 25 ÂµF respectively. Then the Î² value of the transistor is:
A.	35
B.	000.76
C.	25
D.	0.0025
Answer» D. 0.0025

Discussion

82.	An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 ÂµH, and then the series resistance associated with the inductor is: (Qo=100)
A.	0.31 Î©
B.	1.32 Î©
C.	1 Î©
D.	1.561 Î©
Answer» B. 1.32 Î©

Discussion

83.	Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10ÂµH. then the values of the capacitors in the feedback section is:
A.	100 pf, 100 pf
B.	100 pf, 50 pf
C.	70 pf, 130 pf
D.	80 pf, 60 pf
Answer» B. 100 pf, 50 pf

Discussion

84.	The necessary condition for oscillation in a Colpitts oscillator is:
A.	c2/c1=gm/gi
B.	c1/c2=gm/gi
C.	c2/c1= gm*gi
D.	none of the mentioned
Answer» B. c1/c2=gm/gi

Discussion

85.	The criterion on which oscillations are produced in the oscillator circuit is called:
A.	shannonâ€™s criteria
B.	barkhausen criteria
C.	colpitts criteria
D.	none of the mentioned
Answer» C. colpitts criteria

Discussion

86.	The transfer function of an RF oscillator is given by:
A.	a/ (1-ah (Ï‰))
B.	a/ (1+ah (Ï‰))
C.	a/ (-1+ah (Ï‰))
D.	1/ (1-ah (Ï‰))
Answer» B. a/ (1+ah (Ï‰))

Discussion

87.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.
A.	attenuator
B.	amplifier
C.	oscillator
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

88.	Along with a differential amplifier, 1800 hybrid is used both at the input and output.
A.	true
B.	false
Answer» B. false

Discussion

89.	A major advantage of differential amplifiers is:
A.	high gain
B.	low input impedance
C.	higher output voltage swing
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

90.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â uses balanced input and output, meaning that there are 2 signal lines, with opposite polarity at each port.
A.	differential amplifier
B.	distributed amplifier
C.	balanced amplifier
D.	none of the mentioned
Answer» B. distributed amplifier

Discussion

91.	In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.
A.	true
B.	false
Answer» C.

Discussion

92.	Distributed amplifiers offer very high
A.	gain
B.	bandwidth
C.	attenuation
D.	none of the mentioned
Answer» C. attenuation

Discussion

93.	Coupler that is mostly used in balanced amplifiers to achieve the required performance is:
A.	branch line coupler
B.	wilkinson coupler
C.	lange coupler
D.	waveguide coupler
Answer» D. waveguide coupler

Discussion

94.	Bandwidth of balanced amplifier can be an octave or more, but is limited by the bandwidth of the coupler.
A.	true
B.	false
Answer» B. false

Discussion

95.	In conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. But this drawback can be overcome by using:
A.	balanced amplifiers
B.	distributed amplifiers
C.	differential amplifiers
D.	none of the mentioned
Answer» B. distributed amplifiers

Discussion

96.	To flatten the gain response of a transistor:
A.	biasing current has to be increased
B.	input signal level has to increased
C.	increase the operational bandwidth
D.	give negative feedback to the amplifier
Answer» E.

Discussion

97.	High gain is not achievable at microwave frequencies using BJT amplifiers because:
A.	device construction
B.	complex architecture
C.	ports are not matched at high frequencies
D.	none of the mentioned
Answer» D. none of the mentioned

Discussion

98.	If SWR=1.5 with a wavelength of 4 cm and the distance between load and first minima is 1.48cm, then the reflection coefficient is:
A.	0.0126+j0.1996
B.	0.0128
C.	0.26+j0.16
D.	none of the mentioned
Answer» B. 0.0128

Discussion

99.	2 IMPEDANCE MATCHING
A.	swr, first voltage minimum
B.	swr, first voltage maximum
C.	characteristic impedance, first voltage minimum
D.	characteristic impedance, first voltage maximum
Answer» B. swr, first voltage maximum

Discussion

100.	Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is a microwave device in which the frequency of operation is determined by the biasing field strength.
A.	vtm
B.	gyratron
C.	helix bwo
D.	none of the mentioned
Answer» C. helix bwo

Discussion

Explore topic-wise MCQs in Electrical Engineering.

A parabolic reflector used for reception with the direct broadcast system is 18 inches in diameter and operates at 12.4 GHz. The far-field distance for this antenna is:

In transistor oscillators, FET and BJT are used. Instability is achieved by:

In transistor oscillators, the requirement of a negative resistance device is satisfied using a varactor diode.

To achieve stable oscillation, Zin + ZL=0 is the only necessary and sufficient condition to be satisfied by the microwave oscillator.

For achieving steady state oscillation, the condition to be satisfied in terms of reflection coefficients is:

In a microwave oscillator, a load of 50+50j is connected across a negative resistance device of impedance -50-50j. Steady state oscillation is not achieved in the oscillator.

In microwave oscillators, negative resistance transistors and diodes are used in order to generate oscillations in the circuit.

Any device with negative impedance as its characteristic property can be called:

The equivalent circuit of a quartz crystal has LCR arm capacitance of 12nF and inductance of 3mH and parallel arm capacitance of 4nF. Parallel resonant frequency for the circuit is:

Parallel resonant frequency of quartz crystal is given by:

In the equivalent circuit of a quartz crystal, LCR arm has an inductance of 4 mH and capacitor has a value of 4nF, then the series resonant frequency of the oscillator is:

A quartz crystals equivalent circuit is a series LCR circuit and has a series resonant frequency.

In an oscillator, the resonant feedback circuit must have must have a low Q in order to achieve stable oscillation.

In the plot of reactance v/s frequency of a crystal oscillator, the reactance between series resonant frequency and parallel resonant frequency is:

Quartz crystal and tourmaline used in oscillators work on the principle of:

One condition to be satisfied in an oscillator circuit so that stable oscillations are produced is:

Expression for over all noise figure of a mismatched amplifier is:

Noise equivalent temperature of Wilkinson coupler having a gain of 1/2L is given as:

For a Wilkinson power divider of insertion loss L and the coupler is matched to the external circuitry, and then the gain of the coupler in terms of insertion loss is:

Noise equivalent temperature of a 2 stage cascade network is given by:

Expression for noise of a two port network considering the noise due to transmission line and other lossy components is:

Noise figure can be defined for any microwave network irrespective of any other constraints.

The equivalent noise temperature of a network given the noise figure of the network or system is:

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is defined as the ratio of desired signal power to undesired noise power.

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is defined as the ratio of input signal to noise ratio to the output signal to noise ratio.

Colpitts oscillator in the feedback section has an inductance of 4 mH and capacitors of 12 nH and 4 nH. Then the resonant frequency of Colpitts oscillator is:

Hartley oscillator has inductance values of 12 mH and 4 mH in the feedback section and a capacitor of 4 nF. Then the resonant frequency of the circuit is:

Amplifier efficiency is the ratio of RF output power to DC input power. This parameter determines the performance of an amplifier.

For Colpitts oscillator, the capacitors C1 and C2 in the feedback network are 1 ÂµF and 25 ÂµF respectively. Then the Î² value of the transistor is:

An inductor is operating at frequency of 50 MHz. Its inductance is 0.1 ÂµH, and then the series resistance associated with the inductor is: (Qo=100)

Colpitts oscillator operating at 50 MHz has an inductor in the feedback section of value 0.10ÂµH. then the values of the capacitors in the feedback section is:

The necessary condition for oscillation in a Colpitts oscillator is:

The criterion on which oscillations are produced in the oscillator circuit is called:

The transfer function of an RF oscillator is given by:

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is a non linear circuit that converts DC power to an AC waveform of desired frequency based on the oscillator design.

Along with a differential amplifier, 1800 hybrid is used both at the input and output.

A major advantage of differential amplifiers is:

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â uses balanced input and output, meaning that there are 2 signal lines, with opposite polarity at each port.

In distributed amplifiers, all the FET stages in the amplifier are connected in series to one another.

Distributed amplifiers offer very high

Coupler that is mostly used in balanced amplifiers to achieve the required performance is:

Bandwidth of balanced amplifier can be an octave or more, but is limited by the bandwidth of the coupler.

In conventional amplifiers, a flat gain response is achieved at the cost of reduced gain. But this drawback can be overcome by using:

To flatten the gain response of a transistor:

High gain is not achievable at microwave frequencies using BJT amplifiers because:

If SWR=1.5 with a wavelength of 4 cm and the distance between load and first minima is 1.48cm, then the reflection coefficient is:

2 IMPEDANCE MATCHING

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â is a microwave device in which the frequency of operation is determined by the biasing field strength.