6 Microwave Engineering
different principles. The limitations of conventional tubes at microwave fre-
quencies include lead inductance, stray capacitance and transit time effect,
which assumes signicance as the frequency is raised. The most commonly
used microwave tubes include klystron, reex klystron, magnetron, travel-
ling wave tube (TWT) and the backward wave oscillator (BWO). In view of
the above limitations, a triode may be used up to 1 GHz, whereas the fre-
quencies of operation for other tubes are of a much higher order; for example,
a klystron can be used in the range of 0.4–70 GHz, a TWT can operate over
1–35 GHz and an amplitron can operate over a range of 0.4–9 GHz. These
modied devices operate on the ballistic motion of ...