Design of a Multi-kW Ka-Band Elliptical Beam Amplifier with PPM Focusing

To achieve higher output power while maintaining the compact size and weight of typical PPM-focused TWTs, we have explored options for incorporating a sheet or elliptical cross section electron beam in a coupled cavity or folded waveguide circuit. This approach allows significantly higher beam current to be propagated at a given voltage and magnetic field amplitude than is possible in a round beam. However, there are fundamental design constraints that limit the aspect ratio of the beam and the corresponding circuit designs that can be utilized. Here, some of these constraints will be discussed and designs presented for elliptical beam Ka-band TWTs that are capable of >2 kW output power with a 20 kV, 1A electron beam.