An experimental investigation of a tandem relativistic backward wave oscillator - travelling wave tube amplifier system for generating high-power microwaves

The experimental investigation described in this dissertation demonstrates the feasibility of generating long ({dollar}ge{dollar}50 nsec) pulses of high-power ({dollar}ge{dollar}100 MW), X-band frequency microwaves. In these experiments, a relativistic Backward Wave Oscillator (BWO) is used in tandem with a Traveling Wave Tube (TWT) amplifier to generate microwave radiation. The tandem BWO-TWT system is driven in the TM{dollar}sb{lcub}01{rcub}{dollar} mode by a single annular, relativistic electron beam, which is guided through the two rippled-wall slow wave structures by an applied axial magnetic field.; A special RF sever placed between the BWO and TWT slow wave structures prevents electromagnetic coupling between the oscillator and amplifier while allowing the electron beam to pass from one structure to the other. In this way, the BWO serves to modulate the beam that subsequently drives the TWT producing high-power, phase stable microwave radiation. To obtain microwave pulses with pulsewidths comparable to the electron beam duration, the BWO is operated below saturation levels in order to minimize the pulse-shortening effects that are characteristic of very high-power BWOs. A set of BWO characterization experiments are conducted to determine the optimum operating conditions for this oscillator/modulator.; When driven with a beam of {dollar}sim{dollar}100 nsec duration, the tandem BWO-TWT device is found capable of producing 50-60 nsec wide microwave pulses with peak output powers in excess of 100 MW. Overall beam-to-microwave efficiencies as high as 35% are observed. The operating frequency of the tandem device is tuned between 11-12 GHz by varying the effective energy of the beam.; The tandem BWO-TWT system described here can be scaled up in size to produce peak output power levels in the gigawatt range. This type of system is ideal for use in phased array antenna applications that require an easily controlled source of high power density microwave radiation.