Sapphire based high-power microwave window

Dielectric windows often limit the power handling capability of vacuum electron devices. It is necessary to choose the right dielectric material for high power applications. Depending upon the power level, a range of materials has been used in various systems. The ideal material should have high mechanical strength, high thermal conductivity, high electrical breakdown voltage, low dielectric loss, favourable dielectric constant and easy joinability to metal parts. In order to make a judicious compromise between the material with highly desirable properties and easy availability, sapphire is chosen for the present work. UHV grade joining technique between sapphire and metal has been developed. The dimensions of the dielectric and other components in a pill-box type window design have been optimised using HFSS. The heat transfer and cooling parameters have been optimised using numerical techniques. The design details, fabrication processes and low-power characterisation will be discussed in the paper.