A PM focused ultra-low-noise traveling-wave tube for S-band

This paper describes an ultra low-noise traveling-wave tube using permanent-magnet focusing and which operates over the full octave from 2 to 4 Gc. Terminal noise figure is less than 5.5 db over the band, with all voltages fixed. Developmental models have yielded spot noise figures as low as 3.5 db, and less than 4.5 db across the octave. Gain across the octave is 20 db or greater, the nominal value being 25 db. The tube has been built to withstand a vibration level of 12 g\´s and the package can be operated in any orientation. Low noise amplification is achieved through the use of a conventional multi-anode low-noise gun. The value of the magnetic field at the cathode is increased by flux concentrating rings. A wound-wire "field straightener" serves to short out transverse field components of the Alnico 5 permanent magnet.