Multipactor-susceptible RF windows as power-tunable microwave limiters

Summary form only given. 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. 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. Recent experimental work used a 200 W CW, 2.45 GHz magnetron to direct RF at a Lexan vacuum window with embedded copper wires providing the DC bias. Experimental results confirmed that a DC bias was effective at reducing the RF power threshold for multipactor in argon at 15-25 torr with good reproducibility. Further exploration using argon pressures up to 75 torr showed similar results, though with greater variability. Continuing efforts include tuning the breakdown threshold for different RF powers, measuring RF extinction times, and investigating the use of materials with high secondary electron yields to improve limiter performance.