AR 10013130, Operating And Service Manual

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040609
Application Note #35
Pulse Traveling Wave Tube Amplifiers
AR RF/Microwave Instrumentation's pulse traveling wave tube amplifiers (TWTAs) offer a cost-effective
source of high RF power for applications in which only a low to moderate RF duty cycle is required, i.e.,
where the RF power is on for only a small percentage of the time. A typical application is electromagnetic
compatibility (EMC) RF pulse susceptibility testing. This Application Note discusses the unique
specifications and characteristics applicable to pulse TWTAs.
Pulse-rated TWTAs use a traveling wave tube (TWT) incorporating a control grid that can be used to
turn on and off the TWT's beam current. The TWT acts as an RF amplifier only when the beam is
turned on. Turning the beam off when no RF output is needed results in a significant reduction in power
consumption, and hence reduces the amount of heat to be dissipated.
When compared to a continuous wave (CW)-rated amplifier with similar power specifications, a low to
moderate duty cycle PULSE TWTA typically: uses less AC input power, produces less heat, is smaller and
lighter, costs less, has lower noise power output during the pulse off time, and allows use of peripheral
components (connectors, cables or waveguide, directional couplers, loads, and so forth) with lower CW
power ratings. AR's pulse TWTAs are designed specifically for pulsed applications. They cannot be used
to produce CW output. AR's TP series of pulse TWTAs do incorporate many of the excellent features of
AR's T series of CW TWTAs such as: foldback protection, bright 4 line by 20 character alphanumeric
display and extensive remote status and control via a GPIB (IEEE-488) interface. For CW applications,
contact AR RF/Microwave Instrumentation for information on its extensive line of CW-rated amplifiers.
Unique Specification for Pulse TWTAs
Some unique specification characteristics (those not commonly specified for CW rated amplifiers) of AR
RF/Microwave Instrumentation's pulse TWTAs are listed below, along with a set of typical parameter
values. An explanation of their significance follows.
PULSE CAPABILITY
Pulse Width ....................................................................... 0.07-30 microseconds
Pulse Rate (PRF) ............................................................... 100 kHz maximum
Duty Cycle ........................................................................ 4% maximum
RF Rise and Fall ................................................................ 30ns maximum (10% to 90%)
Delay ................................................................................. 300ns maximum from pulse input to RF 90%
Pulse Width Distortion ..................................................... ±30ns max (50% point of output pulse width
.......................................................................................... compared to 50% points of input pulse width)
Pulse Off Isolation ............................................................. 80 dB minimum, 90 dB typical
NOISE POWER DENSITY .............................................. (Pulse on) xxxx
.......................................................................................... (Pulse off) Minus 140dBm/Hz (typical)
CONNECTORS
Pulse Input ........................................................................ Type BNC female on rear panel