Eigenmodes in open coaxial cylindrical resonators

The electrodynamical properties of open coaxial cylindrical resonators using a partially-conical inner rod are examined on the basis of a resonance criterion for the eigenmodes. Owing to the spectral rearrangement arising from the presence of a coaxial insert, it turns out possible to isolate the desired operating mode from its neighboring competitors. The modelling of an especially designed cavity demonstrates that the corresponding TE-mode spectrum is markedly diluted in the 5-10 GHz range. The coaxial structure with a conical inner rod, is shown to be highly selective, and can find useful applications in high-power gyrotrons and frequency-tunable resonators