Production of high energy microwave beams is hampered by several problems, including low efficiency, surface breakdown inside the tube, air breakdown at the output window (which is typically CVD diamond), and pulse shortening, which limits power output in most designs as input power is increased. Pulse shortening and low duty factor are such serious problems that most current designs can only emit a few hundred joules of energy per pulse.
Another problem is that of focusing the microwave beam. If microwave weapons are to be more than expensive remote tank warmers, the microwave beam will have to be tightly focused. This means significantly shorter wavelengths than the 3-30 cm currently envisaged. Unfortunately, development of millimeter rf sources is still in its infancy. Millimeter waves are also generating interest because of the possibility of using the W-band atmospheric window at 96 GHz for high-resolution radar.
Other chapters cover traveling wave tube (TWT) amplifiers, the effects of plasma inside microwave tubes, cathode materials, gyrotrons, and gyrotron TWTs, in which an electromagnetic wave is amplified at the harmonic of the electron cyclotron frequency. The book does not cover subjects associated with traditional uses of microwaves. For example, the reader is assumed to be familiar with basic microwave concepts such as waveguide transmission modes. The authors are writing from the trenches and occasionally get bogged down in cataloging the various devices made by their colleagues, at the expense of elucidating the basic principles of the devices they are building. Their work seems to take a toll on morale. The general tone of many of the articles is one of grim frustration. Not one of the authors ever cracks a joke throughout the book.