Klystron, Magnetron and TWT

Klystron, Magnetron and TWT
Klystron
 A klystron is a vacuum tube that can be used either as a
generator or amplifier of power at low frequency.
 This was invented by Russell H. varian and Sigurd P. Varian at
Stanford University in 1939.
 The reflex klystron is a single cavity variable frequency time-
base generator of low power and efficiency
 The two-cavity klystron is a widely used microwave amplifier
operated by the principles of velocity and current modulation
 APPLICATION:
 It is widely used as in radar receiver
 Local oscillators in microwave receiver
 Portable microwave rings
 Pump oscillator in parametric amplifier
Two Cavity Klystron
• A two cavity Klystron is widely used operational
amplifier operated by by the principles of velocity
and current modulation.
• All electrons injected from the cathode arrive at the
first cavity with uniform velocity.
• Those electrons passing the first cavity gap at zeros
of the gap voltage (or signal voltage) pass through
with unchanged velocity;
• Those passing through the positive half cycles of the
gap voltage undergo an increase in velocity;
• Those passing through the negative swings of the
gap voltage undergo a decrease in velocity.
Klystron
• The electrons gradually bunch together as they
travel down the drift space.
• The variation in electron velocity in the drift
space is known as velocity modulation.
• The density of the electrons in the second
cavity gap varies cyclically with time.
• The electron beam contains an ac component
and is said to be current-modulated.
• The maximum bunching should occur
approximately midway between the second
cavity grids during its retarding phase;
Two-cavity klystron amplifier
Klystron
• Thus the kinetic energy is transferred from the
electrons to the field of the second cavity.
• The electrons then emerge from the second cavity
with reduced velocity and finally terminate at the
collector.
• The characteristics of a two-cavity klystron amplifier
are as follows:
 Efficiency: about 40%.
 Power output: average power (CW power) is up to 500
kW and pulsed power is up to 30 MW at 10 GHz.
 Power gain: about 30 dB.
MAGNETRON
• A magnetron consists of a cathode which is
used to emit electrons and a number of anode
cavities a permanent magnet is placed on the
backside of cathode.
• The space between anode cavity and cathode is
called interacting space.
• The electron which are emitted from cathode
moves in different path in the interacting space
depending upon the strength of electron and
magnetic field applied to the magnetron.
MAGNETRON
• Magnetron is of 3 types:
 Negative resistance type.
 Cyclotron frequency type.
 Cavity type
• APPLICATION:
 Used as oscillator.
 Used in radar communication.
 Used in missiles.
 Used in microwave oven (in the range of
frequency of 2.5Ghz)
TRAVELING-WAVE TUBES (TWTs}
• A helix traveling-wave tube consists of an
electron beam and a slow-wave structure.
• The electron beam is focused by a constant
magnetic field along the electron
beam and the slow-wave structure.
• This is termed an 0-type traveling-wave tube.
• The slow-wave structure is either the helical
type or folded-back line.
TRAVELING-WAVE TUBES
• The applied signal propagates around the turns of the
helix and produces an electric field at the center of the
helix, directed along the helix axis.
• The axial electric field progresses with a velocity that is
very close to the velocity of light multiplied by the ratio
of helix pitch to helix circumference.
• When the electrons enter the helix tube, an interaction
takes place between the moving axial electric field and
the moving electrons.
• On the average, the electrons transfer energy to the wave
on the helix.
• This interaction causes the signal wave on the helix to
become larger.
• The electrons entering the helix at zero field are not
affected by the signal wave; those electrons entering the
helix at the accelerating field are accelerated, and those
at the retarding field are decelerated.
• As the electrons travel further along the helix, they
bunch at the collector end.
• Each electron in the bunch encounters a stronger
retarding field.
• Then the microwave energy of the electrons is delivered
by the electron bunch to the wave on the helix.
• The amplification of the signal wave is accomplished.
 The characteristics of the traveling-wave tube
are:
 Frequency range: 3 GHz
 higher Bandwidth: about 0.8 GHz
Efficiency: 20 to 40%
Power output: up to 10 kW average
Power gain: up to 60 dB
Slow-Wave Structures
Difference Between Klystron and
Magnetron
REFLEX KLYSTRON MAGNETRON
 It is a linear tube in which  In magnetron the
the magnetic field is applied magnetic field and electric
to focus the electron and field are perpendicular to
electric field is applied to each other hence it is called
drift the electron. as cross field device.
 In klystron the bunching  In magnetron the
takes places only inside the interacting or bunching
cavity which is very small space is extended so the
,hence generate low power efficiency can be increase.
and low frequency.
Difference Between Two Cavity
Klystron and TWT
Two Cavity Klystron TWT
• Electron Beam is • Electron Beam and RF signal
moving from cathode to are travelling in same
anode but radio direction with nearly same
frequency signal is velocity
stationary. • Used helix slow wave
• Used as cavity structure.
resonator • This broad band
amplification
• This is narrow band
amplification

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