Microwave Bits

1. The velocity factor of a transmission line depends onA.temperatureB.skin effectC.relative permittivity of dielectricD.none of the aboveAnswer & ExplanationAnswer: Option CExplanation:r of a dielectric changes with humidity.

2. A loss less line of characteristic impedance Z0 is terminated in pure reactance of -jZ0 value. VSWR is

A.10B.2 C.1D.infinityAnswer & ExplanationAnswer: Option D

Explanation:A pure reactance does not absorb any power. Therefore VSWR is infinite because |rv| = 1.

3. In a klystron amplifier the input cavity is called

A.buncher B.catcher C.Pierce gun D.collectorAnswer & ExplanationAnswer: 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.

View Answer Workspace Report Discuss in Forum4. In a circular waveguide the dominant mode is

A.TE01B.TE11 C.TE20D.TE21Answer & ExplanationAnswer: 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 c = 1.706 D for TE11 modec = 1.029 D for TE21 modec = 0.82 D for TE01 modec = 1.306 D for TM01 mode.

5. The reflection coefficient on a line is 0.2 45. The SWR is

A.0.8B.1.1 C.1.2D.1.5Answer & ExplanationAnswer: Option D Explanation:

Microwave resonators are used in

A.microwave oscillators

B.microwave narrow band amplifier

C.microwave frequency metres

D.all of the above

Answer & ExplanationAnswer:OptionDExplanation:They are used in all the devices.View AnswerWorkspaceReportDiscuss in Forum

7.Assertion (A):TWT uses a focussing mechanism to prevent the electron beam from spreading.Reason (R):In a TWT the electron beam has to travel a much longer distance than in klystron.

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

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.View AnswerWorkspaceReportDiscuss in Forum

8.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

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

9.Which of the following is not a travelling wave?

A.e= Emsin (x- t)

B.e= Emcos (x- t)

C.e= Emsin (t- x)

D.e= Emsin (x)

10.Both Impatt and Trapatt devices use avalanche effect

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation:An Impatt diode hasn+-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.

11.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)

Answer & ExplanationAnswer:OptionAExplanation:Isolation equals coupling plus directivity.View AnswerWorkspaceReportDiscuss in Forum

12.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

Answer & ExplanationAnswer:OptionBExplanation:Charging current and MVAR are proportional to frequency.View AnswerWorkspaceReportDiscuss in Forum

13.Loss angle of a good quality cable is about

A.1B.30

C.70D.90

Answer & ExplanationAnswer:OptionAExplanation:For ideal dielectric loss angle is zero. For good quality cables, loss angle is very small, about 1 only.View AnswerWorkspaceReportDiscuss in Forum

14.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)

Answer & ExplanationAnswer:OptionCExplanation: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 GHz2. Power output - 10 kW to several hundred kW3. Power gain - 60 dB (nominal value)4. Efficiency - about 40%.A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.

15.In the given figure reflection coefficient at load is

A.0.6

B.- 0.6

C.0.4

D.- 0.4

Answer & ExplanationAnswer:OptionBExplanation:

16.Which of the following lines is non-radiating?

A.Open two wire

B.Coaxial

C.Both

D.None of the above

Answer & ExplanationAnswer:OptionBExplanation:Since fields are confirmed within a coaxial cable it is non-radiating.View AnswerWorkspaceReportDiscuss in Forum

17.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.





Answer & ExplanationAnswer:OptionAExplanation:Matched load means no reflections.View AnswerWorkspaceReportDiscuss in Forum

18.Skin effect is more pronounced at high frequencies.

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation:Skin effect increases as frequency increases.View AnswerWorkspaceReportDiscuss in Forum

19.Assertion (A):The phenomenon of differential mobility is called transferred electron effect.Reason (R):GaAs exhibits transferred electron effect.





Answer & ExplanationAnswer:OptionBExplanation:A Gunn diode uses GaAs which has a negative differential mobility,i.e., a decrease in carrier velocity with increase in electric field.This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.View AnswerWorkspaceReportDiscuss in Forum

20.Which of the following devices uses a helix?

A.Klystron amplifier

B.Klystron oscillator

C.TWT

D.Both (a) and (b)

Answer & ExplanationAnswer:OptionCExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

21.Which of the following parameters is negligible in transmission lines?

A.RB.L

C.CD.G

Answer & ExplanationAnswer:OptionDExplanation:Shunt conductance can be neglected in most of calculations.View AnswerWorkspaceReportDiscuss in Forum

22.The width of a radio beam from a 1 m diameter parabolic antenna at 10 GHz is about

A.100B.50

C.5D.1

Answer & ExplanationAnswer:OptionCExplanation:.View AnswerWorkspaceReportDiscuss in Forum

23.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

Answer & ExplanationAnswer:OptionAExplanation:Applegate diagram is distance time plot.View AnswerWorkspaceReportDiscuss in Forum

24.Impedance level of Impatt diodes is generally lower than that of Gunn diodes

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation:An Impatt diode hasn+-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.View AnswerWorkspaceReportDiscuss in Forum

25.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

Answer & ExplanationAnswer:OptionDExplanation:A quarter wave line o.c. at far end behaves as a series tuned circuit.

26.A line has Z0= 300 0 . IfZL= 150 0 , reflection coefficient is

A.0.5B.0.3333

C.-0.3333D.-0.5

Answer & ExplanationAnswer:OptionCExplanation:Reflection coefficientView AnswerWorkspaceReportDiscuss in Forum

27.Assertion (A):A backward wave oscillator has an internal positive feedback.Reason (R):A positive feedback is necessary for sustained oscillations.





Answer & ExplanationAnswer:OptionBExplanation: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.View AnswerWorkspaceReportDiscuss in Forum

28.In a microstrip transmission the signal can be easily redirected by changing the centre strip.

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation: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.View AnswerWorkspaceReportDiscuss in Forum

29.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

Answer & ExplanationAnswer:OptionAExplanation: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.View AnswerWorkspaceReportDiscuss in Forum

30.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

Answer & ExplanationAnswer:OptionDExplanation:.

31.In the given figure the time taken by the wave to make one round trip is

A.10ns

B.20ns

C.30ns

D.40ns

Answer & ExplanationAnswer:OptionDExplanation:

View AnswerWorkspaceReportDiscuss in Forum

32.For a 50 resistor for 3 GHz application, the stray capacitance should be less than

A.1 F

B.1nF

C.1pF

D.0.1pF

Answer & ExplanationAnswer:OptionDExplanation:XCshould be at least ten times greater than R. Therefore for 50 resistor at 3 GHz, C should be less than 0.1 pF.View AnswerWorkspaceReportDiscuss in Forum

33.In a travelling wave tube distributed interaction between an electron beam and a travelling wave takes place

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.View AnswerWorkspaceReportDiscuss in Forum

34.The fabrication of microstrip line is done by

A.photo etching

B.printed circuit technique

C.oxidation

D.cladding

Answer & ExplanationAnswer:OptionBExplanation:Printed circuit techniques is used for micro strip line.View AnswerWorkspaceReportDiscuss in Forum

35.The condition of minimum distortion in a transmission line is

A.RL = 1

B.R = 0

C.

D.

Answer & ExplanationAnswer:OptionDExplanation:The condition for minimum distortion is found by equatingThe result is.

36.The action of backward wave oscillator is similar to that of

A.klystron amplifier

B.reflex klystron oscillator

C.TWT

D.magnetron

Answer & ExplanationAnswer:OptionCExplanation: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.View AnswerWorkspaceReportDiscuss in Forum

37.In the given figure the reflection coefficient at source end is

A.1B.-1

C.1/3D.-1/3

Answer & ExplanationAnswer:OptionCExplanation:.View AnswerWorkspaceReportDiscuss in Forum

38.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.






39.In a backward wave oscillator the wave travelling along the line winds itself back and forth

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation: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.View AnswerWorkspaceReportDiscuss in Forum

40.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

Answer & ExplanationAnswer:OptionDExplanation:Becausev= 1 at each end, the line voltage will not reach a steady value and oscillations will continue indefinitely.

41.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.





Answer & ExplanationAnswer:OptionAExplanation:Since the fields are confined, there is no radiation.View AnswerWorkspaceReportDiscuss in Forum

42.Reflex klystron oscillator is essentially a low power device

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 10 MW to about 2 W3. Efficiency - 10 - 20 %Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.View AnswerWorkspaceReportDiscuss in Forum

43.A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is

A.4000

B.400

C.40

D.4

Answer & ExplanationAnswer:OptionBExplanation:and is independent of line length.View AnswerWorkspaceReportDiscuss in Forum

44.A matched generator (Zg= Z0) with 1 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

Answer & ExplanationAnswer:OptionAExplanation:Since all ports matched, input SWR = 1. No power is reflected and Pin= P4= 1 W.This power splits between ports 1 and 2. Therefore P1= P2= 0.5 , P3= 0.View AnswerWorkspaceReportDiscuss in Forum

45.Which TM mode in rectangular waveguide has lowest cutoff frequency?

A.TM11B.TM01

C.TM10D.TM21

Answer & ExplanationAnswer:OptionAExplanation:Hz= 0

Ex= ZTMHyEy= ZTMHxwhere E0is the amplitude of the wave.The expressions for , c,fc, g,are the same as for TE waves.For TM wave the lowest cut off frequency in rectangular wave guide is for TM11mode.If, the cutoff frequency for TM11mode is about 12% more than that for TE20mode.

46.A resistive microwave load with ZL= 150 is connected to 50 coaxial line. SWR is

A.more than 3

B.less than 3

C.equal to 3

D.either (a) or (c)

Answer & ExplanationAnswer:OptionCExplanation:


47.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

Answer & ExplanationAnswer:OptionDExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.View AnswerWorkspaceReportDiscuss in Forum

48.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

Answer & ExplanationAnswer:OptionCExplanation:Since the two wire radiators are at 90 to each other, they have to be excited 90 out of phase with each other.View AnswerWorkspaceReportDiscuss in Forum

49.A waveguide section in a microwave circuit acts as

A.LP filter

B.Bandpass filter

C.HP filter

D.Band stop filter

Answer & ExplanationAnswer:OptionCExplanation:It allows high frequencies.View AnswerWorkspaceReportDiscuss in Forum

50.In a klystron amplifier dc electron velocity isv0and dc electron charge density is0the dc beam current is

A.0v0

B.0/v0

C.v0/0

D.(v0/0)2

Answer & ExplanationAnswer:OptionAExplanation:= coulomb |sec|m2= current density.

1.The directivity in a receiving antenna1. increases the intercept area in forward direction2. reduces the noise picked up from other sources3. provides a means of discriminating against undesired signals originating in directions other than in which the desired transmitter lies.Which of the above statements are correct?

A.1 only

B.1 and 2 only

C.1, 2 and 3

D.2 and 3 only

Answer & ExplanationAnswer:OptionCExplanation:All the three are correct.View AnswerWorkspaceReportDiscuss in Forum

2.Assertion (A):PIN diode can be used as attenuator and limiter.Reason (R):PIN diode has a thin intrinsic layer.





Answer & ExplanationAnswer:OptionBExplanation:A PIN diode has an intrinsic (i) layer betweenpandnlayers. When reverse bias is applied depletion layers are formed atp-iandi-njunctions.The effective/width of depletion layer increases by the width ofilayer. It can be used as a voltage controlled attenuator.At high frequencies the rectification effect ceases and impedance of diode is effectively that ofilayer.This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.View AnswerWorkspaceReportDiscuss in Forum

3.The bunching action which occurs in multicavity klystron amplifier can be represented by Applegate diagram

A.TrueB.False

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 10 kW to several hundred kW3. Power gain - 60 dB (nominal value)4. Efficiency - about 40%.A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.View AnswerWorkspaceReportDiscuss in Forum

4.The cut off wavelength in circular waveguide

A.guide diameter

B.square of guide diameter

C.cube of guide diameter

D.square root of guide diameter

Answer & ExplanationAnswer:OptionAExplanation:Some applications require dual polarization capability. Circular waveguide has this capability.These analysis uses cylindrical coordinates.In circular waveguide TE11mode has the lowest cut off frequency and is the dominant mode.If D is diameter of waveguidec= 1.706 D for TE11modec= 1.029 D for TE21modec= 0.82 D for TE01modec= 1.306 D for TM01mode.View AnswerWorkspaceReportDiscuss in Forum

5.In Reflex Klystron oscillator the focussing electrode is at a high potential

A.TrueB.False

Answer & ExplanationAnswer:OptionBExplanation: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 GHz2. Power output - 10 MW to about 2 W3. Efficiency - 10 - 20 %Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.

6.Consider the following statements1. Impedance of Gunn diode is about tens of ohms.2. Impedance of Impatt diode is a few ohms.3. Impedance of Impatt diode are of the same order.4. Impedance of Impatt diode is more than that of Gunn diode.Which of the above statement are correct?

A.all

B.1 and 2 only

C.1, 2 and 3

D.1, 2 and 4

Answer & ExplanationAnswer:OptionBExplanation:A Gunn diode uses GaAs which has a negative differential mobility,i.e., a decrease in carrier velocity with increase in electric field.This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.An Impatt diode hasn+-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.View AnswerWorkspaceReportDiscuss in Forum

7.In high frequency circuits impedance matching can be done by1. open circuited stubs2. short circuited stubs3. transformerWhich of the above correct?

A.1, 2 and 3

B.1 and 2 only

C.1 and 3 only

D.2 and 3 only

Answer & ExplanationAnswer:OptionAExplanation:All the three can be used for impedance matching in high frequency circuits.View AnswerWorkspaceReportDiscuss in Forum

8.The directive gain of a transmitting antenna is proportional to

A.its cross-sectional area

B.square of cross-sectional area

C.square root of cross-sectional area

D.cube root of cross-sectional area

Answer & ExplanationAnswer:OptionAExplanation:and is thus proportional to cross sectional area.View AnswerWorkspaceReportDiscuss in Forum

9.In a loss line RL< Z0, then

A.Reflection coefficient is zero

B.Reflection coefficient is

C.Reflection coefficient is negative

D.Reflection coefficient is positive

Answer & ExplanationAnswer:OptionCExplanation:Since RL< Z0,vis negative.View AnswerWorkspaceReportDiscuss in Forum

10.Assertion (A):A backward wave oscillator can be used as a sweep generator.Reason (R):The frequency of oscillation of a backward wave oscillator can be changed by varying the voltage which controls the beam velocity.





Answer & ExplanationAnswer:OptionAExplanation: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.

6.Consider the following statements1. Impedance of Gunn diode is about tens of ohms.2. Impedance of Impatt diode is a few ohms.3. Impedance of Impatt diode are of the same order.4. Impedance of Impatt diode is more than that of Gunn diode.Which of the above statement are correct?

A.all

B.1 and 2 only

C.1, 2 and 3

D.1, 2 and 4

Answer & ExplanationAnswer:OptionBExplanation:A Gunn diode uses GaAs which has a negative differential mobility,i.e., a decrease in carrier velocity with increase in electric field.This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.An Impatt diode hasn+-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.View AnswerWorkspaceReportDiscuss in Forum

7.In high frequency circuits impedance matching can be done by1. open circuited stubs2. short circuited stubs3. transformerWhich of the above correct?

A.1, 2 and 3

B.1 and 2 only

C.1 and 3 only

D.2 and 3 only

Answer & ExplanationAnswer:OptionAExplanation:All the three can be used for impedance matching in high frequency circuits.View AnswerWorkspaceReportDiscuss in Forum

8.The directive gain of a transmitting antenna is proportional to

A.its cross-sectional area

B.square of cross-sectional area

C.square root of cross-sectional area

D.cube root of cross-sectional area

Answer & ExplanationAnswer:OptionAExplanation:and is thus proportional to cross sectional area.View AnswerWorkspaceReportDiscuss in Forum

9.In a loss line RL< Z0, then

A.Reflection coefficient is zero

B.Reflection coefficient is

C.Reflection coefficient is negative

D.Reflection coefficient is positive

Answer & ExplanationAnswer:OptionCExplanation:Since RL< Z0,vis negative.View AnswerWorkspaceReportDiscuss in Forum

10.Assertion (A):A backward wave oscillator can be used as a sweep generator.Reason (R):The frequency of oscillation of a backward wave oscillator can be changed by varying the voltage which controls the beam velocity.





Answer & ExplanationAnswer:OptionAExplanation: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.

11.If a line having Z0= 300 0 W is open circuited at far end, VSWR is

A.0B.1

C.D.2

Answer & ExplanationAnswer:OptionCExplanation:If line is o.c. |v| = 1 and VSWR= .View AnswerWorkspaceReportDiscuss in Forum

12.Iffis the frequency of electromagnetic wave,fcis cutoff frequency, then in a rectangular waveguide

A.attenuation is low whenf>fc

B.attenuation is low whenf> Z0, then

A.Z0= ZL(VSWR)

B.ZL= Z0(VSWR)

C.ZL= Z0(VSWR - 1)

D.ZL= Z0VSWR

Answer & ExplanationAnswer:OptionBExplanation:If ZL>> Z0, |v|and VSWR. Therefore ZL= Z0(VSWR).View AnswerWorkspaceReportDiscuss in Forum

25.The inductance of a twin feeder used to connect antenna to TV receiver is about

A.0.2 H/m

B.0.6 H/m

C.1.6 H/m

D.10 H/m

Answer & ExplanationAnswer:OptionC

26.When resonant cavities are coupled together the result is

A.one resonant frequency

B.nresonant frequencies

C.resonant frequencies

D.either (b) or (c)

Answer & ExplanationAnswer:OptionBExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

27.For a rectangular waveguide having widthaand heightb, the cutoff wavelength for TM11mode is equal to

A.

B.

C.

D.


28.The path length between ports 1 and 2 for the two waves in a hybrid ring is

A.1

B.

C.

D.

Answer & ExplanationAnswer:OptionCExplanation:The quantities required to be measured in microwave circuits are frequency, power and impedance.Microwave frequency measurement is done by slotted line, resonant cavities and transfer oscillator.Microwave power measurement uses bolometers and microwave power meters.A self balancing bridge working on the principle of power substitution is commonly used.Microwave impedance measurement is done by measurement of reflection coefficient and VSWR.A slotted line and probe is a basic tool for these measurements.' Network analyser enables rapid impedance measurement over a broad frequency range.View AnswerWorkspaceReportDiscuss in Forum

29.The radiation resistance of a circular loop of one turn is 0.01 ohm. For 5 turn loop the radiation resistance is

A.0.002

B.0.01

C.0.05

D.0.25

Answer & ExplanationAnswer:OptionDExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

30.As wavelength decrease the size of high directivity antenna

A.decreases

B.increases

C.is not affected

D.either (b) or (c)

Answer & ExplanationAnswer:OptionAExplanation:No answer description available for this question.Let us discuss.

31.Which of the following modes of transmission will not be supported by a rectangular waveguide?

A.TE15B.TE12

C.TM11D.TM10

Answer & ExplanationAnswer:OptionDExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

32.In a circular waveguide with radiusr, the dominant mode is

A.TM01B.TE01

C.TM11D.TE11

Answer & ExplanationAnswer:OptionBExplanation:Some applications require dual polarization capability. Circular waveguide has this capability.These analysis uses cylindrical coordinates.In circular waveguide TE11mode has the lowest cut off frequency and is the dominant mode.If D is diameter of waveguidec= 1.706 D for TE11modec= 1.029 D for TE21modec= 0.82 D for TE01modec= 1.306 D for TM01mode.View AnswerWorkspaceReportDiscuss in Forum

33.If 'a' is the width of rectangular wave guide and '' is the wave length, then

A.

B.

C.

D.


34.A parametric amplifier uses

A.non linear resistance

B.non linear reactance

C.either (a) or (b)

D.neither (a) nor (b)

Answer & ExplanationAnswer:OptionBExplanation:In a parametric amplifier the non-linear element is varactor diode or inductor.View AnswerWorkspaceReportDiscuss in Forum

35.Assertion (A):Impatt diode can be used in both amplifiers and oscillators.Reason (R):Impatt diode has a low resistance.





Answer & ExplanationAnswer:OptionBExplanation:An Impatt diode hasn+-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.

36.Which one of the following can be used for amplification of microwave energy?

A.TWT

B.Magnetron

C.Reflex klystron

D.Gunn diode

Answer & ExplanationAnswer:OptionAExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

37.If ZTEis wave impedance for TE waves, Edis maximum dielectric strength of insulating material,aandbare the width and height of a rectangular wave guide, the maximum power handling capability Pmaxfor TE10mode is

A.

B.

C.

D.


38.At frequencies of 10 MHz and higher the impedance represented by ground is primarity

A.resistive

B.inductive

C.capacitive

D.partly resistive and partly capacitive

Answer & ExplanationAnswer:OptionCExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

39.A disadvantage of microstrip line as the connections of compared to strip line is that former

A.do not lend themselves to printed circuit

B.are more likely to radiate

C.are bulky

D.are more expensive and complex


40.As frequency increases, the transmission efficiency

A.decreases

B.increases

C.is not affected

D.either (a) or (c)

Answer & ExplanationAnswer:OptionB

41.A circular polarizer converts a linearly polarized wave into a circularly polarised wave.

A.TrueB.False


42.If D is diameter of circular waveguide the cutoff wave-length for TE11mode is equal to

A.1.706 D

B.2.11 D

C.0.82 D

D.0.41 D

Answer & ExplanationAnswer:OptionAExplanation:Some applications require dual polarization capability. Circular waveguide has this capability.These analysis uses cylindrical coordinates.In circular waveguide TE11mode has the lowest cut off frequency and is the dominant mode.If D is diameter of waveguidec= 1.706 D for TE11modec= 1.029 D for TE21modec= 0.82 D for TE01modec= 1.306 D for TM01mode.View AnswerWorkspaceReportDiscuss in Forum

43.The external magnetic field in a magnetron is such that lines are

A.parallel to the axis of cathode

B.perpendicular to the axis of cathode

C.inclined to the axis of cathode

D.either (b) or (c)

Answer & ExplanationAnswer:OptionAExplanation:The operation of magnetron is based on interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at 90 with respect to each other.In a magnetron three forces act on electron viz. force due to electric field (equal to -eE), force due to magnetic field [equal to -e(vx B)] and centrifugal force (equal tomv2/r).The path of the electron can be found by balancing these three forces. Magnetron can be of three types i.e., negative resistance device, cyclotron frequency device and travelling wave or cavity device.In negative resistance magnetron use is made of the negative resistance between two anode segments.It has low efficiency and is used at frequencies less than 0.5 GHz.In cyclotron magnetron a synchronism exists between ac component of electric field and periodic oscillation of electrons in a direction parallel to the field.It is used for frequencies higher than 100 MHz.A cavity magnetron has a number of cylindrical cavities in the interaction region.The cavity magnetron is the most common type of magnetron. Its features are :1. Frequency range - 500 MHz to 10 GHz2. Power output - 250 kW (pulses)3. Efficiency - about 50%It is used in radar systems, industrial heating systems and microwave ovens.View AnswerWorkspaceReportDiscuss in Forum

44.Varactor diodes use

A.silicon

B.GaAs

C.either (a) or (b)

D.neither (a) nor (b)

Answer & ExplanationAnswer:OptionCExplanation:No answer description available for this question.Let us discuss.View AnswerWorkspaceReportDiscuss in Forum

45.A circular waveguide carries TE11mode whole radial electric field is given byEr= E0j1(r) sin V/mwhereris radial distance in cm from the axisThe cut off wavelength is

A.10 cm

B.3cm

C.2cm

D.8 cm

Answer & ExplanationAnswer:OptionA

46.Assertion (A):Impatt diode is an avalanche diode.Reason (R):Avalanche breakdown phenomenon occurs when ap-njunction is reverse biased.





Answer & ExplanationAnswer:OptionBExplanation:An Impatt diode hasn+-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.View AnswerWorkspaceReportDiscuss in Forum

47.A radar has a maximum range of 120 km. The maximum allowable pulse repetition frequency for unambiguous reception is

A.1250B.330

C.2500D.8330


48.In a line with finite attenuation

A.power transmission is least efficient when there are no standing waves on the line

B.power transmission is most efficient when there are no standing waves on line

C.Load power depends on phase constant

D.standing waves will always exist on the line

Answer & ExplanationAnswer:OptionBExplanation:If standing waves are not there, whole of the power is absorbed by load.View AnswerWorkspaceReportDiscuss in Forum

49.In the given figure a short circuited transmission line resonator Ifn= 1, 2, 3...

A.For series reasonance l=nand for parallel resonance

B.For series resonanceand for parallel resonance l=n

C.l=nfor both series and parallel resonance

D.for both series and parallel resonance


50.The electric field in a TWT due to applied signal

A.is directed along the helix axis

B.is directed radially from helix axis

C.is inclined to the helix axis by about 60

D.is inclined to the helix axis by about 45

Answer & ExplanationAnswer:OptionAExplanation: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 GHz2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz3. Efficiency - about 5 to 20%4. Noise - about 5 dB for low power TWT 25 dB for high power TWTTWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc

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