Study and Applications of Wideband Oscillations in High-Power Pulsed Traveling-Wave Tubes

Summary form only given. Recently it has been shown that wideband microwave pulses are more effective than those composed of single-frequency carriers at generating radio-frequency upset in electronic systems. Nonlinearity in semiconductor junctions down-convert the modulation frequencies off the carrier into baseband signals that may cause logic errors, oscillations and instability in the circuits. These effects are more readily produced by RF pulses which contain many fast transients. We present an alternative and simpler method for generating complex RF waveforms rather than using the conventional synthesizer-amplifier approach. Traveling-wave tubes (TWT) may be configured as oscillators if a portion of the output is fed back to the input. When the feedback is sufficient to drive the tube into saturation, gain and phase nonlinearity in the TWT, and feedback time delay, may create conditions where the oscillations have chaotic amplitudes. This behavior has been demonstrated theoretically and experimentally in continuous-wave (CW) TWT amplifiers where the system parameters are assumed to be steady state and the dynamics are statistically in equilibrium. The resulting amplitude modulation is usually fairly low and, therefore, not particularly interesting for RF effects work. In pulsed TWT´s, where the rise time of the beam is comparable to the time delay of the feedback loop, transient dynamics in the system generate chaotic waveforms that are highly modulated (very broadband). In some instances the output amplitude during the first few microseconds was observed to switch from nearly noise levels to fully saturated output and back off in just a few RF cycles. Results are presented from measurements on a 2 kW, Ku-band pulsed TWTA and an L-band TWT with pulse modulated feedback. The data show the dependence of the output amplitude and spectra on the feedback parameters. Wideband chaotic oscillations are demonstrated in both cases. The effects generated in advanced C- OS logic gates when their inputs are excited by these waveforms are also discussed