InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The reverse voltage applied to a varactor diode |
| Answer» The action of varactor diode is due to the capacitance of depletion layer. The thickness of depletion layer depends on the reverse bias which should not cause breakdown. | |
| 2. |
A cavity resonator is |
| Answer» Hollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field. These enclosures are called cavity resonators. | |
| 3. |
If antenna diameter is increased four times, the maximum range is increased by a factor of |
| Answer» Range of radar is proportional to antenna diameter. | |
| 4. |
Atomic and molecular resonance is observed in many substances |
| Answer» Atomic and molecular distances are very small. Therefore resonance can occur only at microwave frequencies. | |
| 5. |
In a circular waveguide TE mode has lowest cutoff frequency |
| Answer» 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. | |
| 6. |
The number of TV channels which can be accommodated in a spectrum of 300 MHz is about |
| Answer» A TV channel has a bandwidth about 5 MHz. Hence 300 MHz spectrum can accommodate about 50 channels. | |
| 7. |
The noise figure of multicavity klystron amplifier is very low |
| Answer» 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. | |
| 8. |
Roughly the time required for microwave cooking as compared to conventional cooking is |
| Answer» Time required for microwave cooking is much less than the time required for conventional cooking. | |
| 9. |
If the minimum range of a radar is to be doubled, the peak power has to be increased by a factor of |
| Answer» Range = (power)025. | |
| 10. |
Which mode has the lowest cut off frequency in circular wave guides? |
| Answer» 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. | |
| 11. |
A wave E cos (b - ω) is a backward wave. |
| Answer» It is a forward wave because as t increases, x increases. | |
| 12. |
In the given figure the E and H lines in a coaxial cable |
| Answer» H lines are concentric circles around conductor and E lines are radial. | |
| 13. |
A coaxial RF cable has a characteristic impedance of 50 Ω and C equal to 40 pF/m. The inductance is |
| Answer» . | |
| 14. |
In a microwave coaxial line, the maximum operating frequency is and breakdown strength of dielectric is E' Then maximum power handling capacity is proportional to |
| Answer» Power handling capacity μ (voltage)2 and is inversely proportional to f2 max. | |
| 15. |
A reflex klystron oscillator is a |
| Answer» 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. | |
| 16. |
Impedance inversion may be obtained with |
| Answer» Impedance inversion occurs when load impedance is not matched with characteristic impedance of line. | |
| 17. |
Power gain of a multicavity klystron amplifier is |
| Answer» 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. | |
| 18. |
In a multicavity klystron amplifier the signal to be amplified develops an ac voltage of signal frequency across the gap in buncher cavity |
| Answer» 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. | |
| 19. |
If VSWR is infinite, the transmission line is terminated in |
| Answer» and . Since VSWR = ∞, |rv| = 1. This can happen if ZL = 0 or ZL = ∞, i.e., line is o.c or s.c. | |
| 20. |
If a short line is terminated in characteristic impedance it behaves as an infinite line. |
| Answer» In a line terminated by Z0, there are no reflections. | |
| 21. |
Ga As exhibits negative differential mobility |
| Answer» 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. | |
| 22. |
Microwave links are typically 50 km apart |
| Answer» Earth's curvature limits the distance between microwave links. | |
| 23. |
For matching over a range of frequencies in a transmission line it is best to use |
| Answer» Double stub is useful for matching over a range of frequencies. | |
| 24. |
The expression H = C cos(B) cos(A) is for |
| Answer» In TM mode Hz = 0. | |
| 25. |
If a line having Z = 300 ∠ 0 W is short circuited at far end, VSWR is |
| Answer» If line is s.c |rv| = 1 and VSWR = ∞. | |
| 26. |
A klystron amplifier generally uses Pierce gun |
| Answer» 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. | |
| 27. |
A coaxial line has L = 500 H/m and C = 50 F/m. The characteristic impedance is |
| Answer» . | |
| 28. |
The main feature of a parametric amplifier is |
| Answer» Since reactance does not contribute thermal noise to the circuit, it is a low noise device. | |
| 29. |
A pulsed radar produces 1 μ sec pulses at a rate of 1000 per second. The duty cycle is |
| Answer» 1 x 10-6 x 1000 = 0.001. | |
| 30. |
When a line is loaded the characteristic impedance is equal to |
| Answer» or . | |
| 31. |
Which device has internal positive feedback? |
| Answer» 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. | |
| 32. |
The semiconductor diode which can be used in switching circuit in microwave range is |
| Answer» A PIN diode has an intrinsic (i) layer between p and n layers. When reverse bias is applied depletion layers are formed at p-i and i-n junctions. The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator. At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer. This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc. | |
| 33. |
In the given figure the reflected current wave after first reflection is |
| Answer» | |
| 34. |
A line has an attenuation of 0.054 Np/m. The attenuation in decibels is |
| Answer» 0.054 x 8.68 = 0.47 dB/m. | |
| 35. |
If a line is open circuited Z = Z tanh (g). |
| Answer» 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 micromave power meters. A self balancing bridge working on the principle of power substitution is commomly 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. | |
| 36. |
A reflex klystron oscillator uses |
| Answer» 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. | |
| 37. |
The directive gain of a transmitting antenna is |
| Answer» | |
| 38. |
A duplexer is used to |
| Answer» Same antenna is used for transmission and reception. | |
| 39. |
A branched duplexer requires |
| Answer» A branched duplexer funds use in narrow bandwidth applications. TR tube stands for transmit-receive tube and ATR tube stands for antitransmit receive tube. Both these tubes are used in branched duplexer. | |
| 40. |
In a backward wave oscillator the wave |
| Answer» 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. | |
| 41. |
If D is diameter of circular waveguide the cutoff wave-length for TE mode is equal to |
| Answer» 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. | |
| 42. |
The external magnetic field in a magnetron is such that lines are |
| Answer» 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 (v x B)] and centrifugal force (equal to mv2/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 GHz 2. Power output - 250 kW (pulses) 3. Efficiency - about 50% It is used in radar systems, industrial heating systems and microwave ovens. | |
| 43. |
In a line with finite attenuation |
| Answer» If standing waves are not there, whole of the power is absorbed by load. | |
| 44. |
In a TWT the amplitude of resultant wave travelling down the helix remains constant |
| Answer» The signal gets strengthened. | |
| 45. |
In the given figure forward current wave has a magnitude of |
| Answer» | |
| 46. |
In a vacuum tube, the transit time of electron between cathode and anode is important at |
| Answer» At high frequencies transit time is large as compared to the period of microwave signal. | |
| 47. |
The electric field in a TWT due to applied signal |
| Answer» 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. | |
| 48. |
A transmission line has = 300 Ω and = (300 - 300) ohm. The transmission coefficient is |
| Answer» Transmission coefficient = 1.265 ∠- 18.43°. | |
| 49. |
In a reflex klystron oscillator, repeller electrode is at |
| Answer» 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. | |
| 50. |
A quarter wave line short circuited at load end behaves as |
| Answer» A quarter wave line short-circuited at far end behaves as a parallel tuned circuit. | |