Frequency study of microwave generation in an axially extracted virtual cathode oscillator

Summary form only given. In virtual cathode oscillators (vircators) the axial electric field, driven by either reflecting electrons between the real and virtual cathodes or oscillations of the virtual cathode, couples with axially symmetric transverse magnetic waveguide mode (TM/sub 0m/). To study this mechanism in detail the dependence of radiation frequency on cathode diameter, output waveguide diameter, and anode-cathode (A-K) gap spacing was studied experimentally in an axially-extracted vircator at Himeji Institute of Technology. The radiation frequency decreased with increasing A-K gap spacing for a constant cathode diameter. The maximum power emission was observed at the A-K gap spacing for which reflecting trapped electrons between the real and virtual cathodes determine the radiation frequency. The measurement of power density profile in the radial and azimuthal directions showed the radiation pattern of TM/sub 01/ mode, in agreement with the observed frequency which satisfies the dispersion relation of TM/sub 01/ mode in the circular output waveguide.