Basic Properties of Gyrotrons Based on the Use of Planar Photonic-Structure Cavities

The implementation of subterahertz gyrotrons operating at high cyclotron harmonics inevitably involves the use of oversized operating cavities having dense mode spectra. This leads to a problem of the mode selectivity; namely, parasitic waves excited at lower cyclotron harmonics should be suppressed. In this article, we develop an approach based on the use of cavities with mode selection element and study a gyrotron cavity based on Bragg-type “photonic structures” formed by corrugated mirrors. Such a cavity should solve the problem of selectivity, as it supports high-Q quasi-critical modes only within a narrow frequency band of the Bragg resonance. The results of simulations and analytical estimations for Q-factors of these modes are presented in this article. Analytical estimations for starting currents of high-harmonic gyrotrons based on such “photonic-structure” cavities are expressed and discussed.