Experimental investigation of twin traveling wave tube amplifiers driven by a single relativistic backward wave oscillator

The experimental research presented in this thesis establishes the feasibility of a novel microwave phased antenna array. The outputs of multiple high power Traveling Wave Tube (TWT) amplifiers driven by a single high power Backward Wave Oscillator (BWO) source feed the antenna. To test the concept we drove twin TWTs with a single BWO, simultaneously supplied by three independent relativistic electron beams. Experimental investigations of the system showed that the twin TWTs produced high power ({dollar}>{dollar}1 MW) signals which were phase-coherent, to within the {dollar}pm{dollar}10{dollar}spcirc{dollar} accuracy of the phase measurement, for the duration of the BWO's {dollar}sim{dollar}20 nsec long microwave pulse. Further, the TWTs maintain phase coherence over a wide frequency range of 900 MHz as the TWT's rf input was tuned by adjusting the oscillation frequency of BWO. Depending on the beam conditions and rf input frequency to the TWTs, gains of 0-25 dB were found with 3 dB bandwidths ranging from 400-800 MHz.; Fundamental research investigating the operation of the BWO and the TWT was also performed. A series of single BWO experiments investigated output microwave properties of frequency, pulse width, bandwidth, and power. By parameterizing these properties in terms of the driving electron beam's effective energy we found the operating point of a BWO could be predicted. We further found pulse width, bandwidth, and output microwave power had distinct trends which could be explained by investigating the saturation mechanism of the BWO. Studies showed that device saturation was a result of the trapping of beam electrons in the large, potential fields of the beam's slow space charge wave. An efficiency comparison between experiment and an analytical single wave model of the BWO's nonlinear behavior revealed a strong correlation. The influence of magnetic field strength on the output microwave properties of the BWO and TWT are also presented and show that the BWO has dramatic decrease in output power, but the TWT does not, for the investigated ranges of applied magnetic field. This was predicted by our assumption that power reduction is a result of the concurrent excitation the beam's slow space charge and slow cyclotron waves.