Design of a Sheet-Beam Electron-Optical System for a Microfabricated W-Band Traveling-Wave Tube Using a Cold Cathode

A design of a sheet-beam electron-optical system (EOS) for a microfabricated W-band traveling-wave tube (TWT) is presented. The proposed TWT is based on a rectangular field-emitter array (FEA) and a planar helix slow-wave structure with straight-edge connections (PH-SEC). The PH-SEC is designed to work with a 5-kV and 10-mA sheet electron beam. The particle-in-cell simulation results show that the TWT can give 3.7-W peak power at 110 GHz with a 3-dB bandwidth of 60%. The EOS consists of a novel beam-forming electrode, a novel anode, a magnetic circuit to provide solenoidal focusing magnetic field, and a depressed collector. Except for the magnetic circuit, all components are compatible with microfabrication. Moreover, the anode and the collector can be fabricated together with the PH-SEC using the same process steps. Using an FEA with the dimensions of 1000 x500 mu m(2), a beam of cross section 160 x 40 mu m(2) is generated and under ideal conditions 100% transmission is achieved through a 25-mm-long drift tunnel of cross section 240x100 mu m(2). The effects of misalignments of the FEA, anode, and the magnetic circuit are investigated, and the limits on misalignments are determined to achieve satisfactory beam transmission.