Lets see about different types of microwave tube amplifiers.............................
But before that letz see what are microwave tube amplifiers???
Microwave tubes may seem "old school" for college whippersnappers, but one tube can do the work of many, many solid state power amplifiers. The tube industry is alive and well, but there is not a great number of engineers in this field. If you are thinking about making a career out of tubes, this could work out, because the average age of a real tube engineer is somewhere around 90!!!
Microwave tubes have special additional components compared to amplifier tubes such as resonant cavities that usually can't be built from glass.The reason for this is that to create a resonant cavity we require vacuum inside the resonant cavity...and since glass can be complex shaped it cannot hold vacuum .
Why do we use microwave tubes and not the conventional low frequency tubes?
Conventional low frequency tubes like triodes fail to operate at microwave frequencies(MF) because the electron transit time from cathode to grid becomes do large that it cannot produce microwave oscillations.In order for an amplifier to work efficiently at the desired frequency the propagation times must be insignificant. And we see that conventional tubes have a significant propagation times and hence cannot be used at microwave frequencies.
The device parameters for this tubes starts taking a dominating part in circuit and hence successful oscillations aren't met.There are also other limitations attched to them:
CLASSIFICATION
Microwave tubes can be broadly classifies into two categories
But before that letz see what are microwave tube amplifiers???
Microwave tubes may seem "old school" for college whippersnappers, but one tube can do the work of many, many solid state power amplifiers. The tube industry is alive and well, but there is not a great number of engineers in this field. If you are thinking about making a career out of tubes, this could work out, because the average age of a real tube engineer is somewhere around 90!!!
Microwave tubes have special additional components compared to amplifier tubes such as resonant cavities that usually can't be built from glass.The reason for this is that to create a resonant cavity we require vacuum inside the resonant cavity...and since glass can be complex shaped it cannot hold vacuum .
Why do we use microwave tubes and not the conventional low frequency tubes?
Conventional low frequency tubes like triodes fail to operate at microwave frequencies(MF) because the electron transit time from cathode to grid becomes do large that it cannot produce microwave oscillations.In order for an amplifier to work efficiently at the desired frequency the propagation times must be insignificant. And we see that conventional tubes have a significant propagation times and hence cannot be used at microwave frequencies.
The device parameters for this tubes starts taking a dominating part in circuit and hence successful oscillations aren't met.There are also other limitations attched to them:
- Interelectrode capacitance
- Dielectric losses
- Lead inductance effect
- Effects due to radiation losses and radio frequency(RF) losses
- Skin effect(which is is the tendency of an alternating current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor)
- Gain-bandwidth limitations
CLASSIFICATION
Microwave tubes can be broadly classifies into two categories
In O-Type tube , a magnetic field whose axis coincides with the electron beam is used to hold the beam togetheras it travels the length of the tube
This is just a rough classification of the microwave tubes...................
Basically there are only main two types of microwave tubes
We will see the tubes in detail in the next post...............
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This is just a rough classification of the microwave tubes...................
Basically there are only main two types of microwave tubes
- Tubes with electromagnetic cavity(klystrons and magnetrons)
- Tubes with slow wave circuits(traveling wave tubes)
We will see the tubes in detail in the next post...............
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