Twt theory pg one 6-23-20

Effects of Input Conditions on TWTs
Ring Loop backward wave amplifiers have very 
narrow active bandwidths for which gain is possible 
but the active bandwidth is voltage tunable. There-
fore such TWTs were used originally as tunable filters 
with gain. These had applications in electronic 
countermeasure systems.
Input conditions that affect TWT operation include 
beam current, drive power, helix voltage, drive 
frequency, and heater voltage. For a given beam 
current, the power output of a TWT amplifier is a 
function of the RF drive power as shown in Figure 3. 
The gain is essentially constant at a given frequency 
for low RF drive levels, but decreases at higher levels. 
When the RF electric field becomes too strong, as a 
result of either amplification or input signal, the 
amount of energy which the beam can deliver to the 
wave reaches a maximum limit. This condition, 
known as the saturation point of the TWT, represents 
the maximum power which can be delivered for a 
given condition of beam current. If the input power is 
increased beyond the value which 
Figure 3

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Traveling Wave Tube
Theory of Operation pg. 3
6/20
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