A novel Ku band microwave source based on a complex extended interaction structure

Summary form only given, as follows. We report an experimental investigation of a novel scheme for efficient interaction between a linear electron beam and the electromagnetic wave in a complex extended interaction cavity. The proposed structure consists of a high R/Q five-gap extended interaction cavity which incorporates a coaxial section of a quarter plasma wavelength, placed between the first and second gaps, for the dual function of frequency tuning and efficiency enhancement. In the coaxial section, beam and wave propagate in separate channels. Frequency tuning is achieved by a ceramic plunger inserted into the wave channel of the coaxial section, hence causing minimum disturbance to the gap fields. An inner channel running through the center conductor of the coaxial section provides a cutoff drift space for ballistic bunching of electrons, an effect that can significantly enhance the interaction efficiency. Oscillation power of 1.35 kW at 16.8 GHz was demonstrated with an interaction efficiency of 31.0%. The total efficiency was further increased to 46% by a two-stage depressed collector. In addition, a helix section is added between the cathode and the complex cavity. This provided phase locking of the oscillator with 50 db demonstrated gain as well as allowing the device to function as a normal and frequency doubling amplifier.