High power X-band helix TWT for airborne radar applications

A PPM-focused, X-band, pulsed helix TWT for airborne radar applications has been designed. The main requirements for this tube are a minimum output power of 8 kW peak with 5% duty cycle over a 10% bandwidth with an efficiency of 30%. The requirements for high average power and efficiency dictate the selection of the design parameters. The electron beam is focused with samarium cobalt periodic permanent magnets and a shadowed control grid allows fast modulation. The rf interaction structure consists of a wound helix supported by three APBN rods inside the vacuum envelope. It comprises two amplifying sections separated by a sever section. The PPM magnetic structure is optimised in order to reduce dimensions and weight at the required focusing axial magnetic field level of about 2800 Gauss. A two stage depressed collector is used to obtain the required overall efficiency.