Microwave Tubes

A microwave tube amplifier uses an axial magnetic field and a radial electric field. This is the

• reflex klystron

• coaxial magnetron

• traveling wave magnetron

• CFA

One of the reasons why vacuum tubes eventually fail at microwave frequencies is that their

• noise figure increases

• transit time becomes too short

• shunt capacitive reactances become too large

• series inductive reactances become too small

One of the following is unlikely to be used as a pulsed device. What is it?

• multicavity klystron

• BWO

• CFA

• TWT

Indicate the false statement.

Transit time in microwave tubes will be reduced if

• the electrodes are brought closer together

• a higher anode current is used

• multiple or coaxial leads are used

• the anode voltage is made larger

The multicavity klystron

• is not a good low level amplifier because of noise

• has a high repeller voltage to ensure a rapid transit time

• is not suitable for pulsed operation

• needs a long transit time through the buncher cavity to ensure current modulation

Indicate the false statement.

Klystron amplifiers may use intermediate cavities to

• prevent the oscillations that occur in two-cavity klystrons

• increase the bandwidth of the device

• improve the power gain

• increase the efficiency of the klystron

The TWT is sometime preferred to the multicavity klystron amplifier, because it

• is more efficient

• has a greater bandwidth

• has a higher number of modes

• produces a higher output power

The cavity magnetron uses strapping to

• prevent mode jumping

• prevent cathode back heating

• ensure bunching

• improve the phase focusing effect

To avoid difficulties with strapping at high frequencies, the type of cavity structure used in the magnetron is the

• hole and slot

• slot

• vane

• rising sun

The primary purpose of the helix in a traveling wave tube is to

• prevent the electron beam from spreading in the long tube

• reduce the axial velocity of the RF field

• ensure broadband operation

• reduce the noise figure