3. Microwave Semiconductor Devices
• Backward Diode
▫ Used as oscillator and mixer.
▫ Made up of Gallium Arsenide semiconductor.
▫ Used for frequencies up to 200 GHz.
▫ Used for frequencies up to 200 GHz.
• Gunn Diode
▫ Used as oscillator and Amplifier.
▫ Made up of Gallium Arsenide or Indium
Phosphate mixed with Silicon.
▫ Used for frequencies ranging from 4 GHz to
100 GHz.
4. Microwave Semiconductor Devices
• Impatt Diode
▫ Abbreviation taken from word Impact
Avalanche Transit Time.
▫ Used for oscillation and amplification of
▫ Used for oscillation and amplification of
microwave length frequencies.
▫ Used for frequencies up to 200 GHz.
• Schottky Diode
▫ Used for rectification of microwave length
frequencies.
▫ Also used for switching and mixing purposes.
▫ Used for frequencies ranging from 3 MHz to 10
GHz.
5. Microwave Semiconductor Devices
• Tunnel Diode
▫ Used for Oscillation, amplification, mixing
and switching purposes..
▫ Used for frequencies up to 100 GHz.
▫ Used for frequencies up to 100 GHz.
• Varacter Diode
▫ Used in television and FM receiver and
transmitter circuits.
▫ Changes its capacitance with change of bias
applied.
▫ Used for frequencies up to 105 GHz.
6. Microwave Semiconductor Devices
• Transistors
▫ Convectional transistors cannot be used due to
low efficiency and high distortion.
▫ For microwave frequencies, Field Effect
▫ For microwave frequencies, Field Effect
Transistors(FET) made up of GaAs is used.
▫ Used for amplification of higher frequencies.
• Integrated Circuits(I.C.)
▫ At higher frequencies, inductance and
capacitance becomes very small. Hence size of
inductor and capacitor also becomes small.
▫ So hybrid ICs is used for microwave
frequencies.
7. Microwave Tube Devices
• Klystron
▫ High power microwave vacuum tubes.
▫ Velocity-modulated tubes that are used in
radars as amplifiers or oscillators..
radars as amplifiers or oscillators..
▫ Uses the kinetic energy of an electron beam for
the amplification of a high-frequency signal.
▫ Low-power klystrons are used as oscillators in
terrestrial microwave relay communications
links,
▫ While high-power klystrons are used as output
tubes in UHF television transmitters, satellite
communication, radar transmitters, and to
generate the drive power for modern particle
accelerators.
8. Microwave Tube Devices
• Two cavity Klystron
▫ A device for amplifying microwave frequency
signals that achieve high levels of power gain
by applying vacuum tube principles and the
by applying vacuum tube principles and the
concept of “electron bunching”.
▫ Used in satellite systems, television broadcast,
and radar, as well as particle accelerators and
medicine.
• Multi Cavity Klystron
▫ High frequencies can be amplified by multi
cavity klystron.
▫ Used as a medium-, high- and very high-power
amplifier in the UHF and microwave ranges.
9. Microwave Tube Devices
• Magnetron
▫ High-powered vacuum tube that works as a
self-excited microwave oscillator.
▫ Magnetic field is applied longitudinally by an
▫ Magnetic field is applied longitudinally by an
external magnet.
▫ Crossed electron and magnetic fields are used
to produce the high-power output required in
radar equipment.
▫ Capable of generating extremely high
frequencies and also short bursts of very high
power.
▫ An important source of power in radar systems
and in microwave ovens.
10. Microwave Tube Devices
• Travelling Wave Tube
▫ It is a specialized vacuum tube.
▫ Used for amplification at microwave
frequencies between 500 MHz and 300 GHz.
frequencies between 500 MHz and 300 GHz.
▫ Power generation capabilities range from watts
to megawatts.
▫ A major advantage of the TWT over some other
microwave tubes is its ability to amplify a wide
range of frequencies i.e. a large bandwidth.
▫ Two major categories are:
Helix TWT
Coupled cavity TWT
11. Microwave Tube Devices
• Crossed-Field Amplifier
▫ A specialized vacuum tube, used as a
microwave amplifier in very-high-power
transmitters.
transmitters.
▫ Electric and magnetic fields in a CFA are
perpendicular to each other ("crossed fields")..
▫ Peak output powers of many megawatts and
average power levels of tens of kilowatts can be
achieved, with efficiency ratings in excess of 70
percent.
▫ More efficient and capable of much higher
output power.
12. Microwave Tube Devices
• Backward Wave Oscillator
▫ A vacuum tube that is used to generate
microwaves up to the terahertz range.
▫ It belongs to the traveling wave tube family.
▫ It belongs to the traveling wave tube family.
▫ It is an oscillator with a wide electronic
tuning range.
▫ More efficient and capable of much higher
output power.
▫ It can be used as signal source in instruments
and transmitters and broad band noise
sources which used to confuse enemy radar.
