Question 1
A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is
A. 4000 Ω
B. 400 Ω
C. 40 Ω
D. 4 Ω
View Answer
Question 2
A line has a phase constant of 29.8 rad/m. At 1000 MHz the wavelength is
A. 29.8 m
B. 2.98 m
C. 2.1 m
D. 0.21 m
View Answer
Question 3
A line has Z0 = 300 ∠ 0° Ω. If ZL = 150 ∠ 0° Ω, reflection coefficient is
A. 0.5
B. 0.3333
C. -0.3333
D. -0.5
View Answer
Question 4
A line is excited by a 100 V dc source. If reflection coefficients at both ends are 1 each then
A. there will be no oscillations on line
B. there will be only 1 or 2 oscillations on line
C. there will be a finite number of oscillations on line
D. the oscillations will continue indefinitely
View Answer
Question 5
A loss less line of characteristic impedance Z0 is terminated in pure reactance of -jZ0 value. VSWR is
A. 10
B. 2
C. 1
D. infinity
View Answer
Question 6
A matched generator (Zg = Z0) with 1 Ω available. If all ports are matched, the power delivered at ports 1, 2, 3 respectively are
A. 0.5 W, 0.5 W, 0 W
B. 0 W, 0 W, 1 W
C. 0.33 W each
D. 0 W, 0.25 W, 0.25 W
View Answer
Question 7
A quarter wave line open circuited at far end behaves as
A. inductance
B. L and C in parallel
C. capacitance
D. L and C in series
View Answer
Question 8
A resistive microwave load with ZL = 150 Ω is connected to 50 Ω coaxial line. SWR is
A. more than 3
B. less than 3
C. equal to 3
D. either (a) or (c)
View Answer
Question 9
A waveguide section in a microwave circuit acts as
A. LP filter
B. Bandpass filter
C. HP filter
D. Band stop filter
View Answer
Question 10
As the frequency is increased, the charging MVAR in a cable
A. decreases
B. increases
C. remain the same
D. decreases or remains the scheme
View Answer
Question 11
Assertion (A): A backward wave oscillator has an internal positive feedback.Reason (R): A positive feedback is necessary for sustained oscillations.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 12
Assertion (A): A coaxial line is a non-radiating line.Reason (R): In a coaxial line the electric and magnetic fields are confined to the region between the concentric conductors.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 13
Assertion (A): Artificial transmission lines are frequently used in laboratories.Reason (R): An artificial transmission line can be used to represent an actual line and can also be used as a delay circuit, as attenuator, as filter network etc.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 14
Assertion (A): The impedance of a matched load is equal to characteristic impedance of line.Reason (R): A matched termination absorbs all the power incident on it.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 15
Assertion (A): The phenomenon of differential mobility is called transferred electron effect.Reason (R): GaAs exhibits transferred electron effect.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 16
Assertion (A): The reverse saturation current in a semiconductor diode is 4nA at 20°C and 32 nA at 50°C.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 17
Assertion (A): The reverse saturation current in a semiconductor diode is 4nA at 20°C and 32 nA at 50°C.Reason (R): The reverse saturation current in a semiconductor diode doubles for every 10°C rise in temperature.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
View Answer
Question 18
Both Impatt and Trapatt devices use avalanche effect
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
An Impatt diode has n+ - p - i - p + structure and is used with reverse bias.
It exhibits negative resistance and operates on the principle of avalanche breakdown.
Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.
The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.
The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.
Its applications include police radar systems, low power microwave transmitter etc.
Avalanche diode can also be operated in large signal high efficiency mode called Trapped Avalanche Transit Time mode.
The Trapatt oscillations depend on the delay in the current caused by avalanche process.
The avalanche delay makes it possible to increase the diode voltage well above the breakdown voltage.
Therefore a very rapid multiplication of charge carriers occurs. A Trapatt diode is also a negative resistance device.
The features of Trapatt diode oscillator are : Frequency 3 to 50 GHz, Power output 1-3 W, efficiency about 25%.
Its applications are low power doppler radar, microwave beacon landing system etc.
Question 19
For a 50 Ω resistor for 3 GHz application, the stray capacitance should be less than
A. 1 μF
B. 1 nF
C. 1 pF
D. 0.1 pF
View Answer
Answer: Option D
Explanation:
XC should be at least ten times greater than R. Therefore for 50 Ω resistor at 3 GHz, C should be less than 0.1 pF.
Question 20
Impedance level of Impatt diodes is generally lower than that of Gunn diodes
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
An Impatt diode has n+ - p - i - p + structure and is used with reverse bias.
It exhibits negative resistance and operates on the principle of avalanche breakdown.
Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.
The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.
The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.
Its applications include police radar systems, low power microwave transmitter etc.
Question 21
In a backward wave oscillator the wave travelling along the line winds itself back and forth
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.
It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.
The growing RF wave travels in opposite direction to the electron beam.
The frequency of wave can be changed by changing the voltage which controls the beam velocity.
Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.
It features are:
1. Frequency range - 1 GHz to 1000 GHz.
2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).
It is used as signal source in transmitters and instruments.
Question 22
In a circular waveguide the dominant mode is
A. TE01
B. TE11
C. TE20
D. TE21
View Answer
Answer: Option B
Explanation:
Some applications require dual polarization capability. Circular waveguide has this capability.
These analysis uses cylindrical coordinates.
In circular waveguide TE11 mode has the lowest cut off frequency and is the dominant mode.
If D is diameter of waveguide
λc = 1.706 D for TE11 mode
λc = 1.029 D for TE21 mode
λc = 0.82 D for TE01 mode
λc = 1.306 D for TM01 mode.
Question 23
In a directional coupler
A. isolation (dB) equals coupling plus directivity
B. coupling (dB) equals isolation plus directivity
C. directivity (dB) equals isolation plus coupling
D. isolation (dB) equals (coupling) (directivity)
View Answer
Answer: Option A
Explanation:
Isolation equals coupling plus directivity.
Question 24
In a klystron amplifier dc electron velocity is v0 and dc electron charge density is r0 the dc beam current is
A. r0v0
B. r0/v0
C. v0/r0
D. (v0/r0)2
View Answer
Answer: Option A
Explanation:
Err:509
Question 25
In a klystron amplifier the input cavity is called
A. buncher
B. catcher
C. Pierce gun
D. collector
View Answer
Answer: Option A
Explanation:
A Klystron is a vacuum tube used for generation/amplification of microwaves.
An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.
This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.
As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.
Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.
The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.
The input is fed at buncher cavity and output is taken at catcher cavity.
In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.
The features of a multicavity klystron are :
1. Frequency range - 0.25 GHz to 100 GHz
2. Power output - 10 kW to several hundred kW
3. Power gain - 60 dB (nominal value)
4. Efficiency - about 40%.
A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.
Question 26
In a microstrip transmission the signal can be easily redirected by changing the centre strip.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
A Microstrip line has a single dielectric substratc with ground plane on one side and a strip on the other face.
Its special feature is easy access to top surface so that minor adjustments can be made after circuit fabrication.
The high dielectric constant of the substrate reduces guide wavelength and circuit dimensions.
A microstrip line is the most commomly used transmission structure for microwave integrated circuits.
Question 27
In a three cavity klystron amplifier, the oscillations are excited in
A. input cavity
B. output cavity
C. intermediate cavity
D. both (a) and (b)
View Answer
Answer: Option C
Explanation:
A Klystron is a vacuum tube used for generation/amplification of microwaves.
An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.
This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.
As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.
Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.
The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.
The input is fed at buncher cavity and output is taken at catcher cavity.
In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.
The features of a multicavity klystron are :
1. Frequency range - 0.25 GHz to 100 GHz
2. Power output - 10 kW to several hundred kW
3. Power gain - 60 dB (nominal value)
4. Efficiency - about 40%.
A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.
Question 28
In a travelling wave tube distributed interaction between an electron beam and a travelling wave takes place
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In a klystron the resonant structure limits the bandwidth.
A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.
The velocity of wave propagation along the helix structure is less than velocity of light.
The beam and wave travel along the structure at the same speed.
Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.
Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.
The main features of TWT are :
1. Frequency range - 0.5 GHz to 90 GHz
2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz
3. Efficiency - about 5 to 20%
4. Noise - about 5 dB for low power TWT 25 dB for high power TWT
TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.
Question 29
In a turnstile antenna two-half wave resonant wire radiators are placed at 90° to each other in the same plane and are excited
A. in phase
B. in phase opposition
C. 90° out of phase with each other
D. 45° out of phase with each other
View Answer
Answer: Option C
Explanation:
Since the two wire radiators are at 90° to each other, they have to be excited 90° out of phase with each other.
Question 30
In a TWT the amplitude of resultant wave travelling down the helix
A. increases exponentially
B. increases linearly
C. decreases exponentially
D. is almost constant
View Answer
Answer: Option A
Explanation:
In a klystron the resonant structure limits the bandwidth.
A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.
The velocity of wave propagation along the helix structure is less than velocity of light.
The beam and wave travel along the structure at the same speed.
Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.
Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.
The main features of TWT are :
1. Frequency range - 0.5 GHz to 90 GHz
2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz
3. Efficiency - about 5 to 20%
4. Noise - about 5 dB for low power TWT 25 dB for high power TWT
TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.
Question 31
Microwave resonators are used in
A. microwave oscillators
B. microwave narrow band amplifier
C. microwave frequency metres
D. all of the above
View Answer
Answer: Option D
Explanation:
They are used in all the devices.
Question 32
Reflex klystron oscillator is essentially a low power device
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
It uses a single cavity resonator for generating microwave oscillations.
Its parts are electron gun, resonator, repeller and output coupling.
It operates on the principle of positive feed back.
The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.
This positive feedback supports oscillations. Its feature are:
1. Frequency range - 2 to 100 GHz
2. Power output - 10 MW to about 2 W
3. Efficiency - 10 - 20 %
Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.
Question 33
Skin effect is more pronounced at high frequencies.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Skin effect increases as frequency increases.
Question 34
The action of backward wave oscillator is similar to that of
A. klystron amplifier
B. reflex klystron oscillator
C. TWT
D. magnetron
View Answer
Answer: Option C
Explanation:
It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.
It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.
The growing RF wave travels in opposite direction to the electron beam.
The frequency of wave can be changed by changing the voltage which controls the beam velocity.
Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.
It features are:
1. Frequency range - 1 GHz to 1000 GHz.
2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).
It is used as signal source in transmitters and instruments.
Question 35
The diagram to show distance time history of electrons in klystron amplifier is called
A. apple gate diagram
B. asynchronous diagram
C. bunching diagram
D. velocity modulation diagram
View Answer
Answer: Option A
Explanation:
Applegate diagram is distance time plot.
Question 36
The fabrication of microstrip line is done by
A. photo etching
B. printed circuit technique
C. oxidation
D. cladding
View Answer
Answer: Option B
Explanation:
Printed circuit techniques is used for micro strip line.
Question 37
The frequency of oscillation in a backward wave oscillator can be changed by
A. varying the voltage which controls beam velocity
B. varying the beam current
C. both by varying the beam current and by light varying the voltage which controls beam velocity
D. changing the rate of thermionic emission
View Answer
Answer: Option A
Explanation:
It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.
It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.
The growing RF wave travels in opposite direction to the electron beam.
The frequency of wave can be changed by changing the voltage which controls the beam velocity.
Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.
It features are:
1. Frequency range - 1 GHz to 1000 GHz.
2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).
It is used as signal source in transmitters and instruments.
Question 38
The reflection coefficient on a line is 0.2 ∠45°. The SWR is
A. 0.8
B. 1.1
C. 1.2
D. 1.5
View Answer
Question 39
The velocity factor of a transmission line depends on
A. temperature
B. skin effect
C. relative permittivity of dielectric
D. none of the above
View Answer
Answer: Option C
Explanation:
∈r of a dielectric changes with humidity.
Question 40
The width of a radio beam from a 1 m diameter parabolic antenna at 10 GHz is about
A. 100°
B. 50°
C. 5°
D. 1°
View Answer
Answer: Option C
Explanation:
.
Question 41
Which of the following devices uses a helix?
A. Klystron amplifier
B. Klystron oscillator
C. TWT
D. Both (a) and (b)
View Answer
Answer: Option C
Explanation:
In a klystron the resonant structure limits the bandwidth.
A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.
The velocity of wave propagation along the helix structure is less than velocity of light.
The beam and wave travel along the structure at the same speed.
Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.
Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.
The main features of TWT are :
1. Frequency range - 0.5 GHz to 90 GHz
2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz
3. Efficiency - about 5 to 20%
4. Noise - about 5 dB for low power TWT 25 dB for high power TWT
TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.
Question 42
Which of the following devices uses a slow wave structure?
A. Klystron two cavity amplifier
B. Klystron multicavity amplifier
C. Reflex klystron oscillator
D. TWT
View Answer
Answer: Option D
Explanation:
In a klystron the resonant structure limits the bandwidth.
A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.
The velocity of wave propagation along the helix structure is less than velocity of light.
The beam and wave travel along the structure at the same speed.
Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.
Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.
The main features of TWT are :
1. Frequency range - 0.5 GHz to 90 GHz
2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz
3. Efficiency - about 5 to 20%
4. Noise - about 5 dB for low power TWT 25 dB for high power TWT
TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.
Question 43
Which of the following is not a travelling wave?
A. e = Em sin (βx - ωt)
B. e = Em cos (βx - ωt)
C. e = Em sin (ωt - βx)
D. e = Em sin (βx)
View Answer
Answer: Option D
Explanation:
In a travelling wave both x and t increase simultaneously so that a constant phase point moves in the direction of positive (or negative) x.
Question 44
Which of the following lines is non-radiating?
A. Open two wire
B. Coaxial
C. Both
D. None of the above
View Answer
Answer: Option B
Explanation:
Since fields are confirmed within a coaxial cable it is non-radiating.
Question 45
Which of the following parameters is negligible in transmission lines?
A. R
B. L
C. C
D. G
View Answer
Answer: Option D
Explanation:
Shunt conductance can be neglected in most of calculations.
Question 46
Which TM mode in rectangular waveguide has lowest cutoff frequency?
A. TM11
B. TM01
C. TM10
D. TM21
View Answer
Answer: Option A
Explanation:
Hz = 0
Ex = ± ZTM Hy
Ey = ± ZTM Hx
where E0 is the amplitude of the wave.
The expressions for β, λc, fc, λg, a are the same as for TE waves.
For TM wave the lowest cut off frequency in rectangular wave guide is for TM11 mode.
If , the cutoff frequency for TM11 mode is about 12% more than that for TE20 mode.