High efficiency, phase-locked operation of the harmonic-multiplying inverted gyrotwystron oscillator

The inverted gyrotwystron (phigtron) is a millimeter wave frequency-doublin g amplifier that has been demonstrated to produce over 300 kW peak power at twice the input frequency (centered at f(in) = 16.85 GHz and f(out) = 33.7 GHz) over a 0.5% bandwidth with a saturated gain of 30 dB and efficiency g reater than 35% [1]. The device has also been studied both theoretically an d experimentally in a different operating regime where frequency-doubled, p hase-locked oscillation is possible. A signal, injected via a fundamental g yro-traveling wave tube input section, modulated a 55 kV, 10 A electron bea m. After transit through a drift section, the prebunched electron beam prod uced phase-locked, second harmonic oscillations in a TE03 mode output cavit y. RF output centered at either of two frequencies, 34.42 and 34.62 GHz, wi th a maximum output power of 180 KW, an efficiency of 32% and a locked sign al gain of 35 dB was measured. A theoretical prediction of locking bandwidt h, a design overview, and the experimental results are presented followed b y a summary and discussion of the results.