Planar-Integrated PPM Focusing System Design for W-Band Multibeam Folded Waveguide TWTs

This article investigates a planar distributed four-beam electron optics system for the folded waveguide traveling wave tube (TWT) operating in W-band. The planar integrated periodic permanent magnetic (PIPPM) focusing system is constructed to achieve a planar multibeam array with adjacent beam separation of 20 mm by 1-D compression, where the axial
${B}_{\text {z}}$
-field can reach 0.312 T. In this magnet system, the pole piece with an innovation step is considered to efficiently reduce interference of the transverse magnetic field while conditioning the transverse magnetic field
${B}_{\text {x}}/{B}_{\text {z}}$
to be 1%. The optimization of the magnet structure and a thorough analysis of the magnetic saturation of the pole piece are conducted to ensure the transmission stability of the four-beam array and reduce the overall volume. Opera-3-D simulation demonstrates that the four-beam array consistently achieves a long-distance transmission rate of over 99.3% with the PIPPM system. The developed electron optics system may be applied for the folded waveguide TWTs in W-band for phased array radar systems in the future.