Frequency and Power Measurements on the Harmonic Recirculating Planar Magnetron

Abstract

The harmonic recirculating planar magnetron (HRPM) is a frequency-agile, multispectral HPM source. The HRPM implements an $L$ -band oscillator (LBO) and an $S$ -band oscillator (SBO) near 1 and 2 GHz, respectively. The novel coaxial-all-cavity-extraction (CACE) method was implemented to extract power from the SBO. The two oscillators demonstrated harmonic frequency locking, where the SBO frequency locked to the LBO second harmonic frequency. The two oscillators are concluded to operate as a damped, driven, harmonic oscillator system. In the locked state, the LBO acts as the driving oscillator, the SBO acts as the driven oscillator, and the coupling mechanism between the two oscillators is the harmonic content in the electron spokes as they propagate directly from the LBO to the adjacent SBO. The two primary variables studied in this system are the LBO harmonic frequency and the SBO quality factor, $Q$ . In isolated SBO experiments, the dominant operating state of the magnetron was the $5\pi $ /6 mode. However, when operated in tandem with the LBO, the SBO was forced to operate in the $\pi $ -mode. Output powers in HRPM experiments generated SBO powers of 9.5 ± 1.4 MW at high $Q$ , 19 ± 6 MW at moderate $Q$ , and 28 ± 9 MW at low $Q$ . Output powers in the isolated SBO configuration were not significantly different from the HRPM. By experimentally manipulating the hub drift direction and altering the evolution of harmonic content received by the SBO, the locked state was significantly diminished, suggesting that the beam spokes play a crucial role.