Performance monitoring of high-power microwave radar klystron units with acoustic emission technology

Microwave tubes have advanced to a near-commodity status, with applications in consumer products like microwave ovens to industrial processes like drying of polymers, vulcanization, emulsification, thawing, tempering and even in preservation of fruits and vegetables. High-power microwave tubes are also used extensively for communication systems and radars in both the commercial sector and for military applications. Unlike their low-power counterparts, microwave tubes with output powers of greater than 50 W average power are costly and therefore not readily discarded or even economically replaced. At present, computer based data acquisition units using multiple electrical measurements from the operating microwave tubes are available. Although they have certain advantages, the data buffering and analysis become problematic when radar units are operated at high pulse repetition rates. The authors proposed and successfully used acoustic emission as a much simpler, nondestructive method to monitor the performance of high-power pulsed magnetron radar tubes in a laboratory environment. This paper reports on the extension of acoustic emission technology to US Navy radar installations operated with expensive high-power klystron radar tubes. The correlation between radio frequency outputs and acoustic emissions for high-power microwave klystron systems was investigated. Changes in pulse outputs from klystrons corresponded to changes in acoustic emissions captured by acoustic emission sensors. This correlation proved the applicability of acoustic emission technology for in-situ performance monitoring of high-power klystron systems.