A W-band third harmonic gyrotron with a photonic band gap cavity

The design and experimental results of a third harmonic gyrotron oscillator using a photonic band gap (PBG) cavity are presented. The cavity is a two-dimensional PBG structure formed by triangular arrays of copper rods. The lattice spacing is 2.96 mm and the radius of rods is 1.08 mm. The PBG cavity is designed to support a TE04-like mode resonant at 95 GHz. Experimental operation of a 40 kV, 4 A third harmonic gyrotron oscillator with the PBG cavity is conducted. The third harmonic oscillation with step tunable frequency from 89.3 GHz to 96.6 GHz is observed when the magnetic field varies from 1.15 T to 1.22 T.