Microwave Engineering Cavity Klystron - Microwave Engineering

What is Microwave Engineering Cavity Klystron?

There is a need of some special tubes called as Microwave tubes for the generation and amplification of Microwaves. Of them all, Klystron is an vital one.

Electron beams and cavity resonators are the vital elements of Klystron. Electron beams are bent from a source and the cavity klystrons are employed to intensify the signals. A collector is present at the end to collect the electrons. The whole set up is as shown in the resulting figure.
cavity_klystrons

The electrons released by the cathode are enhanced towards the first resonator. The collector at the end is at the similar potential as the resonator. Therefore, typically the electrons have a continuous speed in the gap between the cavity resonators.

Originally, the first cavity resonator is provided with a weak high frequency signal, which has to be amplified. The signal will start an electromagnetic field inside the cavity. This signal is approved through a coaxial cable as shown in the resulting figure.

coaxial_cable

Due to this field, the electrons that pass over the cavity resonator are modified. On incoming at the second resonator, the electrons are made with another EMF at the same frequency. This field is robust enough to extract a large signal from the second cavity.

Cavity Resonator

First let us try to comprehend the constructional details and the working of a cavity resonator. The resulting figure indicates the cavity resonator.
cavity_resonator

A simple resonant circuit which contains of a capacitor and an inductive loop can be linked with this cavity resonator. A conductor has free electrons. If a charge is practical to the capacitor to get it charged to a voltage of this polarity, many electrons are detached from the upper plate and introduced into the lower plate.

The plate that has additional electron deposition will be the cathode and the plate which has minor number of electrons becomes the anode. The resulting figure shows the charge deposition on the capacitor.
capacitor_plates

The electric field lines are absorbed from the positive charge on the way to the negative. If the capacitor is charged with opposite polarity, then the way of the field is also reversed. The movement of electrons in the tube, establishes an irregular current. This irregular current gives rise to irregular magnetic field, which is out of phase with the electric field of the capacitor.

When the magnetic field is at its supreme strength, the electric field is zero and after a while, the electric field develops maximum while the magnetic field is at zero. This exchange of strength happens for a cycle.

Closed Resonator

The less significant the value of the capacitor and the inductivity of the loop, the complex will be the oscillation or the resonant frequency. As the inductance of the loop is very minor, high frequency can be got.

To yield higher frequency signal, the inductance can be auxiliary reduced by insertion more inductive loops in parallel as shown in the resulting figure. This results in the formation of a closed resonator having very high frequencies.
closed_resonator

In a secure resonator, the electric and magnetic fields are limited to the inner of the cavity. The first resonator of the cavity is eager by the external signal to be amplified. This signal need have a frequency at which the cavity can resonate. The current in this coaxial cable sets up a magnetic field, by which an electric field originates.

Working of Klystron

To recognize the modulation of the electron beam, entering the first cavity, let's reflect the electric field. The electric field on the resonator keeps on altering its direction of the prompted field. Depending on this, the electrons coming out of the electron gun get their pace controlled.

As the electrons are negatively charged, they are enhanced if moved conflicting to the direction of the electric field. Likewise, if the electrons move in the same direction of the electric field, they get slowed. This electric field keeps on altering; so the electrons are accelerated and decelerated liable upon the change of the field. The resulting figure specifies the electron flow when the field is in the opposite direction.
working_of_klystron

While moving, these electrons enter the field permitted space called as the drift space among the resonators with changing speeds, which generate electron bunches. These groups are shaped due to the difference in the speed of travel.

These bunches enter the second resonator, with an occurrence consistent to the frequency at which the first resonator oscillates. As all the cavity resonators are identical, the drive of electrons makes the second resonator to oscillate. The resulting figure shows the formation of electron bunches.
formation_of_electron_bunches

The prompted magnetic field in the second resonator prompts some current in the coaxial cable, starting the output signal. The kinetic energy of the electrons in the second cavity is nearly identical to the ones in the first cavity and so no energy is taken from the cavity.

The electrons while passing through the second cavity, few of them are quicker while bunches of electrons are decelerated. Therefore, all the kinetic energy is improved into electromagnetic energy to produce the output signal.

Intensification of such two-cavity Klystron is low and hence multi-cavity Klystrons are used.

The resulting figure portrays an instance of multi-cavity Klystron amplifier.
electrons_getting_strengthened

We get weak bunches in the second cavity if the signal applied in the first cavity. These will set up a field in the third cavity, which crops more focused bunches and so on. Henceforth, the amplification is larger.

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