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.
| 51. |
To couple a coaxial line to a parallel wire line it is best to use |
| Answer» A balun gives 4 : 1 impedance transformation. | |
| 52. |
A balun should have |
| Answer» Turn ratio is so selected as to give low SWR at both ports. | |
| 53. |
In a circular waveguide with radius , the dominant mode is |
| 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. | |
| 54. |
A parametric amplifier uses |
| Answer» In a parametric amplifier the non-linear element is varactor diode or inductor. | |
| 55. |
In microwave system the function of mode filter is |
| Answer» Mode filter suppress modes with lower cutoff frequencies. | |
| 56. |
For the strip line in the given figure the capacitance per unit length = |
| Answer» frads/unit length. | |
| 57. |
The total field developed by an antenna array at a distant point is |
| Answer» Since field is a phasor quantity we have to take phasor sum. | |
| 58. |
High speed logic circuits use |
| Answer» High speed means time period is small. Therefore pulses should also have small width. | |
| 59. |
For a circular wave guide |
| Answer» When a circular waveguide is rotated by 90°, the configuration remain the same. | |
| 60. |
In the given figure the reflected voltage wave after first reflection is |
| Answer» . | |
| 61. |
The magnitudes of OC and SC input impedances of a transmission line an 100 Ω and 25 Ω. The characteristic impedance is |
| Answer» | |
| 62. |
A loss less line is terminated in a circular lines are E lines |
| Answer» #NAME? | |
| 63. |
The path length between ports 1 and 2 for the two waves in a hybrid ring is |
| 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 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. | |
| 64. |
In a klystron amplifier the force on all electrons |
| 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. | |
| 65. |
If load impedance Z >> Z, then |
| Answer» If ZL >> Z0, |rv| and VSWR . Therefore ZL = Z0(VSWR). | |
| 66. |
A magnetron requires an external magnetic field with flux lines parallel to axis of cathode |
| 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. | |
| 67. |
When a line short circuited at far end, the minimum voltage occurs at |
| Answer» When a line is short-circuited at far end, the voltage at far end is zero. | |
| 68. |
In a TWT the axial component of electric field advances along the tube |
| 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. | |
| 69. |
If other parameter are constant, transmission loss at 5 GHz as compared to that at 0.5 GHz is |
| Answer» As frequency increases, transmission loss increases slightly. | |
| 70. |
A (75 - 50) ohm load is connected to a coaxial of Z = 75 ohm at 10 GHz. The best method of matching is to connect |
| Answer» A short-circuited stub is a suitable method of matching. | |
| 71. |
The width of a radio beam from a 1 m diameter parabolic antenna at 1 GHz is about |
| Answer» Beam width between nulls of a parabolic antenna . Therefore 50° is the nearest value. | |
| 72. |
A 75 ohm line is first short terminated and minima locations are noted. Then the short is replaced by resistive load and minima location are again noted. If minima location are not altered and VSWR is 3, the value of resistive load is |
| Answer» rv and VSWR . | |
| 73. |
In a klystron amplifier the bunching effect |
| 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. | |
| 74. |
If a line having Z = 300 ∠ 0 W is open circuited at far end, VSWR is |
| Answer» If line is o.c. |rv| = 1 and VSWR = ∞. | |
| 75. |
If is the frequency of electromagnetic wave, is cutoff frequency, then in a rectangular waveguide |
| Answer» Wavelength should be less than cutoff wavelengths. Therefore frequency should be higher than cutoff frequency for minimum attenuation. | |
| 76. |
A magnetron has a cylindrical cathode surrounded by an anode structure having cavities opening into interaction space by means of slots |
| 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. | |
| 77. |
The correct sequence of parts in klystron amplifier are |
| Answer» Cathode is the first part and anode is the last. | |
| 78. |
In high frequency circuits impedance matching can be done by Which of the above correct? |
| Answer» All the three can be used for impedance matching in high frequency circuits. | |
| 79. |
The directive gain of a transmitting antenna is proportional to |
| Answer» and is thus proportional to cross sectional area. | |
| 80. |
In a loss line R < Z, then |
| Answer» Since RL < Z0, rv is negative. | |
| 81. |
The directivity in a receiving antenna Which of the above statements are correct? |
| Answer» All the three are correct. | |
| 82. |
The bunching action which occurs in multicavity klystron amplifier can be represented by Applegate diagram |
| 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. | |
| 83. |
The cut off wavelength in circular waveguide |
| 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. | |
| 84. |
In Reflex Klystron oscillator the focussing electrode is at a high potential |
| 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. | |
| 85. |
The component in the given figure is |
| Answer» Z01 provides series inductances and teflon filled low impedance line Z02 provides shunt capacitance. | |
| 86. |
In a directional coupler |
| Answer» Isolation equals coupling plus directivity. | |
| 87. |
As the frequency is increased, the charging MVAR in a cable |
| Answer» Charging current and MVAR are proportional to frequency. | |
| 88. |
Loss angle of a good quality cable is about |
| Answer» For ideal dielectric loss angle is zero. For good quality cables, loss angle is very small, about 1° only. | |
| 89. |
In a three cavity klystron amplifier, the oscillations are excited in |
| 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. | |
| 90. |
In the given figure reflection coefficient at load is |
| Answer» | |
| 91. |
The action of backward wave oscillator is similar to that of |
| 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. | |
| 92. |
In the given figure the reflection coefficient at source end is |
| Answer» . | |
| 93. |
In a backward wave oscillator the wave travelling along the line winds itself back and forth |
| 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. | |
| 94. |
A line is excited by a 100 V dc source. If reflection coefficients at both ends are 1 each then |
| Answer» Because rv = 1 at each end, the line voltage will not reach a steady value and oscillations will continue indefinitely. | |
| 95. |
Both Impatt and Trapatt devices use avalanche effect |
| Answer» 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. | |
| 96. |
Skin effect is more pronounced at high frequencies. |
| Answer» Skin effect increases as frequency increases. | |
| 97. |
In the given figure the time taken by the wave to make one round trip is |
| Answer» | |
| 98. |
The width of a radio beam from a 1 m diameter parabolic antenna at 10 GHz is about |
| Answer» . | |
| 99. |
The diagram to show distance time history of electrons in klystron amplifier is called |
| Answer» Applegate diagram is distance time plot. | |
| 100. |
Impedance level of Impatt diodes is generally lower than that of Gunn diodes |
| Answer» 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. | |