Analytical theory of novel configurations of THz and sub-THz sources driven by linear electron beam

Fundamentals of the theory of classical microwave sources driven by linear electron beams (klystrons, traveling-wave tubes, backward-wave oscillators) were developed long time ago. This theory was developed for devices with an axially symmetric interaction space. For operation in the THz and sub-THz frequency ranges, it is preferable to use planar microwave circuits because at short wavelengths fabrication of only such circuits is possible. This trend makes it necessary to generalize the fundamentals of the existing theory to the case of devices lacking the axial symmetry. Sheet-beam and some configurations of multiple-beam klystrons as well as orotrons and klinotrons can serve as examples of such devices. Present paper summarizes results obtained by the author in recent years. It includes: (a) formulation of the general theory, (b) analysis of mode selectivity in multiple-beam klystrons, (c) analysis of mode coupling effects in sheet-beam klystrons, (d) analysis of the monotron instability in sheet-beam klystrons, (e) analysis of effect of transverse nonuniformity of the RF field on efficiency of such devices, (f) linear and nonlinear theory of the orotron. It is believed that such a simple analytical theory can help designers to evaluate the optimal parameter space where it makes sense to perform a more accurate design of THz sources with the use of available 3D-codes.