Microfabricated Circuits for Sheet Electron Beam Amplifiers in the Upper Millimeter-Wave Spectrum

A meander-line circuit has been examined, and appears suitable, for use as an RF structure for a sheet beam-based traveling wave tube (TWT). The circuit may be fabricated using both, standard brazing and fabrication techniques typically used in TWT manufacture (for a macro-type device operating in current microwave bands), as well as MEMS techniques for a mm-wave band device. This circuit is characterized by a wide-band (to DC), efficient axial coupling impedances or by a uniquely-transverse mode which can be selected through topology and mode launching. Preliminary calculations indicate significant bandwidth is achievable, possibly octaves and almost certainly, whole waveguide bands. Basic electron beam interaction efficiency should be comparable to that of existing TWT devices and energy recovery methods such as those developed for space-based and MPM technologies may be applied to this device. Recently developed technology in the areas of manufacturing, materials and computational models have made this concept viable. Lithographic/microfabrication methods in circuit design make the MEMS circuits scalable (conceivably to THz applications). NC mills with automation and precision allow the low-cost fabrication of the racetrack shapes required for the beam focusing system. And computational modeling facilitates the more-complicated RF matching between waveguide and circuit and 3-D modeling of the electron beam formation and focusing.