Controlled Harmonic Frequency Locking in the Harmonic Recirculating Planar Magnetron

The Harmonic Recirculating Planar Magnetron (HRPM) is a novel, tunable, multi-spectral source of high power microwaves (HPM). Consisting of an L-Band Oscillator (LBO, near 1 GHz) and S-Band Oscillator (SBO, near 2 GHz), the HRPM can generate HPM at multiple frequencies simultaneously by leveraging harmonic frequency locking. In the locked state, the SBO frequency locks to the LBO second harmonic frequency. HRPM operation was characterized in simulation and experiment, with the LBO frequency and SBO quality factor (Q) as the independent variables. It is concluded that the oscillators act as a damped, driven, harmonic oscillator system, where the LBO is the driving oscillator, the SBO is the driven oscillator, and the harmonic content in the beam spokes is the coupling mechanism between them. In standard-HRPM experiments, the SBO generated 9.5 ± 1.4 MW (high Q), 19 ± 6 MW (moderate Q), and 28 ±9 MW (low Q) in the $\pi$-mode. In isolated-SBO experiments, the output power was not significantly different, but the primary operating state was the 5$\pi$/6 mode. Therefore, implementation of the LBO enabled mode control of the SBO.