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 × 500 μm
²
, a beam of cross section 160 × 40 μm
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is generated and under ideal conditions 100% transmission is achieved through a 25-mm-long drift tunnel of cross section 240 × 100 μm
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.