An ultra-low-noise wide-band traveling-wave tube

This paper describes the development of a 2-milliwatt, ultra-low-noise, wide-band traveling-wave tube intended for front-end receiver operation. Methods employed to achieve minimum tube noise figures as low as 2.5 db and broad-band noise figures of less than 3.5 db in the 2500-to-3700- megacycle frequency range are described. Such critical factors in low-noise performance as the cathode, beam-impedance transformation, and rf input sections are discussed, and the reduction of beam noise through proper shaping of the low-potential drift region adjacent to the cathode is considered in detail. The paper also discusses electron-gun design, favorable launching conditions for hollow electron beams, and the magnetic-field configuration required for optimum low-noise performance. In addition, a novel beam-focusing technique is described which permits a considerable reduction in the size, weight, and dc dissipation of the focusing solenoid with no adverse effect on the low-noise performance of the tube. The development of this low-noise traveling-wave tube is sponsored by the Advanced Research Project Agency, with the Rome Air Development Center, Griffis Air Force Base, N.Y., as the monitoring agency.