The frequency increase of the slow-wave electron devices is accompanied by inevitable increase of the electron current density and ohmic losses which strongly restricts the attainable power. In recent years, the use of the spatially-developed sheet electron beams is considered as the major way to develop the medium-power slow-wave devices at mm and sub-THz waves. Hollow electron beams is another configuration which could be used for this purpose. The designs of the oscillators and amplifiers in Ka-band and W-band with both sheet and hollow electron beams are considered and compared.
Space-Harmonic Effects in Helical Slow-Wave Structure --- an Equivalent Circuit Analysis