ABSTRACT
This chapter is devoted to a somewhat briefer treatment of three classes of narrowband microwave sources that are unrelated in their underlying operating principles: virtual cathode oscillators, gyrotrons and electron cyclotron masers, and free-electron lasers. The reason for collecting these microwave sources in a single chapter is that at this time we regard these three classes of narrowband sources as somehow less significant in the field of high power microwaves (HPM) than the sources of Chapters 7 to 9. Let us consider each separately and state the reasons for our admittedly subjective judgment, which varies with the source, recognizing that the significance of any one of them could change with shifts in the technology or application needs.
