Multipactor-Susceptible RF Windows as Power-Tunable Microwave Limiters

Multipactor breakdown on a dielectric may provide automatic protective isolation of electronic circuits such as transmitter-receiver (TR) switches in radar. Prior Monte Carlo simulations suggest the application of a DC bias across a dielectric window in a vacuum-gas environment can lower the threshold for the onset of RF-initiated multipactor [1]. Variation of the DC bias may therefore provide a mechanism by which a microwave window might be tuned such that RF powers exceeding a threshold would result in window breakdown. Previous experimental work confirmed that a DC bias was effective at reducing the threshold for window breakdown to 200 W at 2.45 GHz using argon at 15 -- 25 torr as the background gas. Current research is focusing on operation in a multipactor-dominated pressure regime [2] using 50 \textless\ $p$ \textless\ 500 mTorr. Measurement of RF extinction times and the impact of different window materials on performance are of particular interest, especially materials with high secondary electron yields that are resistant to plasma-induced surface degradation. \\[4pt] [1] P. Zhang et al., Phys. Plasmas 18, 053508 (2011).\\[0pt] [2] J. P. Verboncoeur et al., \textit{Power Modulator Symposium Record}, pp. 13-16, 2006.