A 20 to 40-KMC backward-wave oscillator

A 20 to 40-kmc backward-wave oscillator is described which employs a single-tape helix with a mean diameter of 0.039 inch and a length of 1.75 inch supported internally by a triangular sapphire rod. Physically, the helix is mounted in a hole drilled in the ridge of the output ridge waveguide, and a closely spaced hollow beam is located on the outside of the helix. The output from the helix passes through a short section of coaxial line to the ridge waveguide and then along this guide and through the vacuum envelope to an external mating ridge waveguide. The two sections of guide meet the envelope at an angle of 13 degrees. Output is obtained from the oscillator from 18 to 40 kmc with a voltage range of 300 to 2600 volts. The RF output varies relatively smoothly and exceeds 2 milliwatts with 5-ma collector current over the entire band from 21 to 37.5 kmc. The total variation of power over this band is 6 db. It is expected that this tube will be useful for signal-generator-type applications.