Waveguide Breakdown Effects at High Average Power and Long Pulse Length

An understanding of microwave breakdown in gases has existed for many years 1,2 and has been successfully applied to the design of many high-power microwave systems operating at low duty cycles with pulse lengths on the order of several microseconds. However, recent testing of S-band WR284 microwave hardware filled with sulfur hexafluoride (SF 6 ) and operated at 500- to 1500-kilowatt average power, and 10- to 150-megawatt peak power with 50- to 150-microsecond rectangular pulses showed performance far below expectation. A series of tests and supporting analytical work were undertaken to explain this behavior. These have shown that the empirically observed reduction in peak power handling capability at high levels of average power is caused by the presence of loose particulate matter, microscopic in size and lossy at microwave frequencies. The experimental and analytical proof of the mechanisms responsible for this effect is described. A procedure is 2065 2068 TI-IE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1972