1.
The operating frequency of klystrons and magnetrons is set by the :
(a) cavity resonators
(b) DC supply voltage
(c) input signal frequency
(d) number of cavities
Answer : (a)
2. Decreasing the volume of a cavity causes its resonant frequency to :
(a) increase
(b) decrease
(c) remain the same
(d) drop to zero
Answer : (b)
3. Which of the following is not a microwave tube ?
(a) traveling-wave tube
(b) cathode-ray tube
(c) klystron
(d) magnetron
Answer : (b)
4. In a klystron amplifier, velocity modulation of the electron beam is
produced by the :
(a) collector
(b) catcher cavity
(c) buncher cavity
(d) cathode
Answer : (b)
5. A reflex klystron is used as a(n) :
(a) amplifier
(b) oscillator
(c) mixer
(d) frequency multiplier
Answer : (b)
6. The main advantage of a TWT over a klystron for microwave
amplification is :
(a) lower cost
(b) smaller size
(c) higher power
(d) wider bandwidth
Answer : (d)
7. In a TWT, the electron beam is density-modulated by a :
(a) permanent magnet
(b) modulation transformer
(c) helix
(d) cavity resonator
Answer : (c)
8. High-power TWTs are replacing what in microwave amplifiers ?
(a) MESFETs
(b) magnetrons
(c) klystrons
(d) IMPATT diodes
Answer : (c)
9. Attenuator is used in the traveling wave tube to :
(a) prevent oscillation
(b) increase gain
(c) prevent saturation
(d) all of these
Answer : (a)
10. At what position is the input signal inserted into a traveling-wave tube ?
(a) at the cathode end of the helix
(b) at the collector
(c) at the collector end of the helix
(d) at the control grid of the electron gun
Answer : (a)
11. A traveling wave tube consists of :
(a) electron gun, helix and repeller
(b) electron gun, helix and collector
(c) electron gun, repeller and collector
(d) buncher cavity and catcher cavity
Answer : (b)
12. Which of the following is considered as the major advantage of using a
helix traveling wave tube ?
(a) cheaper
(b) less noise
(c) high power
(d) wide bandwidth
Answer : (d)
1. The production of power at higher frequencies is much simpler than production of
power at low frequencies.
a) True
b) False
Answer: b
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.
a) True
b) False
Answer: b
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
d) None of the mentioned
Answer: a
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
Answer: a
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.
a) True
b) False
Answer: b
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
d) Magnetrons
Answer: b
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
Answer: b
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
c) Magnetrons
d) None o the mentioned
Answer: b
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
Answer: a
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%.
a) True
b) False
Answer: a
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.
a) True
b) False
Answer: b
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.
a) VTM
b) Gyratron
c) Helix BWO
d) None of the mentioned
Answer: b
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.
