This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Micro-wave Tubes”.
1. The production of power at higher frequencies is much simpler than production of power at low frequencies.
Explanation: As frequency increases to the millimeter and sub millimeter ranges, it becomes increasingly more difficult to produce even moderate power with solid state devices, so microwave tubes become more useful at these higher frequencies.
2. Microwave tubes are power sources themselves at higher frequencies and can be used independently without any other devices.
Explanation: Microwave tubes are not actually sources by themselves, but are high power amplifiers. These tubes are in conjunction with low power sources and this combination is referred to as microwave power module.
3. Microwave tubes are grouped into two categories depending on the type of:
a) Electron beam field interaction
b) Amplification method
c) Power gain achieved
d) Construction methods
Explanation: Microwave tubes are grouped into two categories depending on the type of electron beam field interaction. They are linear or ‘O’ beam and crossed field or the m type tube. Microwave tubes can also be classified as oscillators and amplifiers.
4. The klystron tube used in a klystron amplifier is a _________ type beam amplifier.
a) Linear beam
b) Crossed field
c) Parallel field
d) None of the mentioned
Explanation: In klystron amplifier, the electron beam passes through two or more resonant cavities. The first cavity accepts an RF input and modulates the electron beam by bunching it into high density and low density regions.
5. In crossed field tubes, the electron beam traverses the length of the tube and is parallel to the electric field.
Explanation: In a crossed field or ‘m’ type tubes, the focusing field is perpendicular to the accelerating electric field. Since the focusing field and accelerating fields are perpendicular to each other, they are called crossed field tubes.
6. ________ is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity.
a) Backward wave oscillator
b) Reflex klystron
c) Travelling wave tube
Explanation: Reflex klystron is a single cavity klystron tube that operates as on oscillator by using a reflector electrode after the cavity to provide positive feedback via the electron beam. It can be tuned by mechanically adjusting the cavity size.
7. A major disadvantage of klystron amplifier is:
a) Low power gain
b) Low bandwidth
c) High source power
d) Design complexity
Explanation: Klystron amplifier offers a very narrow operating bandwidth. This is overcome in travelling wave tube (TWT). TWT is a linear beam amplifier that uses an electron gun and a focusing magnet to accelerate beam of electrons through an interaction region.
8. In a _________ oscillator, the RF wave travels along the helix from the collector towards the electron gun.
a) Interaction oscillator
b) Backward wave oscillator
d) None o the mentioned
Explanation: In a backward wave oscillator, the RF wave travels along the helix from the collector towards the electron gun. Thus the signal for oscillation is provided by the bunched electron beam itself and oscillation occurs.
9. Extended interaction oscillator is a ________ beam oscillator that is similar to klystron.
a) Linear beam
b) Crossed beam
c) Parallel beam
d) M beam
Explanation: Extended interaction oscillator is a linear beam oscillator that uses an interaction region consisting of several cavities coupled together, with positive feedback to support oscillation.
10. Magnetrons are microwave devices that offer very high efficiencies of about 80%.
Explanation: Magnetrons are capable of very high power outputs, on the order of several kilowatts, and with efficiencies of 80% or more. But disadvantage of magnetron is that they are very noisy and cannot maintain frequency or phase coherence when operated in pulse mode.
11. Klystron amplifiers have high noise output as compared to crossed field amplifiers.
Explanation: Crossed filed amplifiers have very good efficiencies – up to 80%, but the gain is limited to 10-15 db) In addition, the CFA has a noisier output than either a klystron amplifier or TWT. Its bandwidth can be up to 40%.
12. ____________ is a microwave device in which the frequency of operation is determined by the biasing field strength.
c) Helix BWO
d) None of the mentioned
Explanation: Gyratron is a microwave device in which the frequency of operation is determined by the biasing field strength and the electron velocity, as opposed to the dimensions of the tube itself. This makes the gyrator especially useful for microwave frequencies.
Sanfoundry Global Education & Learning Series – Microwave Engineering.
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