Electronics and Communication Engineering - Microwave Communication
It uses a single cavity resonator for generating microwave oscillations.
Its parts are electron gun, resonator, repeller and output coupling.
It operates on the principle of positive feed back.
The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.
This positive feedback supports oscillations. Its feature are:
1. Frequency range - 2 to 100 GHz
2. Power output - 10 MW to about 2 W
3. Efficiency - 10 - 20 %
Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.
- TV tuning
- Active filter
- Microwave frequency multiplication
Varactor diode is used in all the three applications.
- Dissipative attenuator has a fixed value of attenuation.
- Reflective attenuator has a fixed value of attenuation.
- Both dissipative and reflective attenuators are available only with fixed attenuation.
- Both dissipative and reflective attenuators are available with either fixed or variable attenuation.
Both dissipative and reflective attenuators are available with either fixed or variable attenuation.
Impedance inversion occurs when load impedance is not matched with characteristic impedance of line.
A Klystron is a vacuum tube used for generation/amplification of microwaves.
An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.
This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.
As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.
Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.
The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.
The input is fed at buncher cavity and output is taken at catcher cavity.
In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.
The features of a multicavity klystron are :
1. Frequency range - 0.25 GHz to 100 GHz
2. Power output - 10 kW to several hundred kW
3. Power gain - 60 dB (nominal value)
4. Efficiency - about 40%.
A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.