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Velocity-modulated Tubes

Acceleration of electrons by the static anode voltage
Influence of the RF voltage of the resonator
Formation of electron bunches

Figure 1: Formation of electron bunches by velocity modulation

Acceleration of electrons by the static anode voltage Influence of the RF voltage of the resonator Formation of electron bunches
Acceleration of electrons
by the static anode voltage
Influence of the RF voltage
of the resonator
Formation of electron bunches

Figure 1: Formation of electron bunches by velocity modulation

The microwave tube uses transit time in the conversion of dc power to radio-frequency power. The interchange of power is accomplished by using the principle of electron velocity modulation and low-loss resonant cavities in the microwave tube.

Velocity modulation is then defined as that variation in the velocity of a beam of electrons caused by the alternate speeding up and slowing down of the electrons in the beam. This variation is usually caused by a voltage signal applied between the grids through which the beam must pass.
Acceleration of electrons by the static anode voltage: By the anode voltage, the electrons are accelerated uniformly. These get at all times a constant speed of v=d/t. This is shown in the diagram as a uniform slope angle in the bottom region.
Influence of the RF voltage of the resonator: An input resonator is externally excited by a high-frequency oscillation. Through this oscillation, the electrons are either in addition to accelerated or decelerated (during the positive half-wave) or decelerated (negative half-wave). The faster electrons overtake the slower electrons in the drift space.
Formation of electron bunches: Due to the different velocity electron bunches are formed. The electrons were given a large energy due to the high anode voltage. An output resonator is excited by the electron bunches to a powerful oscillation in the frequency of the input oscillation.
The direction of the electron beam and the static electrical field goes to each other parallelly (linearly) into linear beam tubes. Against this the fields influencing the electron beam stand vertically by the electron beam at the cross field tubes.

Microwave Tubes
Density Controlled Tubes
Velocity Modulated Tubes
Crossed Field Tubes
Linear Beam Tubes
a magnetic
field is required
Amplitron
Magnetron
Stabilotron
Traveling Wave Tube
Carcinotron
EIK/EIO
Klystron
Planar Tube (Triode)
Microwave Tubes
Density Controlled Tubes
Velocity Modulated Tubes
Crossed Field Tubes
Linear Beam Tubes
a magnetic
field is required
Amplitron
Magnetron
Stabilotron
Travelling Wave Tube
Carcinotron
EIK/EIO
Klystron
Planar Tube (Triode)

The following table compares with characteristic quantities of the velocity-modulated tubes used in radar technology. Although the planar tube isn't a velocity-modulated tube, it was included into this table for comparison purposes.

  Klystron Traveling Wave Tube EIK/EIO Magnetron Carcinotron planar tube
frequency up to 35 GHz up to 95 GHz up to 230 GHz up to 95 GHz up to 5 GHz up to 1.5 GHz
bandwidth 2 - 4 % 10 - 20 % 0,5 - 1 % a few Megahertz 2 GHz 30 - 50%
power output up to 50 MW up to 1 MW up to 1 kW up to 10 MW 1 W up to 1 MW
amplification up to 60 dB up to 50 dB 40 - 50 dB - - up to 20 dB
function as small-band power amplifier wide-band, lownoise voltage amplifier small-band power amplifier and generator high power oscillator at one frequency frequency-controlled oscillator (VFO) amplifier, oscillator

Table 1: Comparing of velocity-modulated tubes