Voltage-tuned relativistic backward wave oscillator

A relativistic backward wave oscillator for the 10-GHz range with the oscillation frequency tuned within about 5% by changing the accelerating voltage from 600 to 350 kV has been developed. Discrete variations in the voltage and the corresponding frequency tuning from pulse to pulse is rapidly performed by changing the anode-cathode distance in the vacuum diode without breaking vacuum in the working volume. During this, the electron beam power remains almost constant, while the output microwave power varies within 0.4-0.8 GW. The introduction of a dielectric cylinder into the accelerating gap provides a smooth voltage drop from 600 to 350 kV with the corresponding frequency tuning during a 20-ns pulse.