K-band vacuum electron tubes for materials processing: present and future

From the point of view of standard microwave technology at the frequencies 0.915 GHz and 2.45 GHz, the need for using higher ISM frequencies like 5.85 and 24.15 GHz for materials processing applications has to be carefully verified with respect to special physical/engineering advantages or to limits the standard technology meets for the specific problem. Costs evaluation of industrial millimeter (mm)-wave systems have to be competitive, not only to conventional heating, but also to standard microwave solutions. The most important issue here is the availability of mm-wave generators appropriate in power, size and efficiency. The present paper reports on the state-of-the-art and future of modern 24.15 GHz sources like magnetron, extended interaction oscillator, klystron and gyrotron for industrial processing of materials.