DEVELOPMENT OF A VERY LOW NOISE TRAVELING-WAVE TUBE

A description is presented of the early stages in the development of a very low noise traveling-wave tube, designed for operation at S-band frequencies. The tube is to have a minimum gain of 25 db and a maximum tube noise figure of 2 db over the frequency range 2.7 to 3.5 kmc. Theoretical studies were made to determine methods of reducing noise in beam-type devices. Attempts were made to correlate some of the experimental low noise data with the proposed theories. Efforts were directed toward a general re-evaluation of the tube design, especially with regard to its noise performance. Preliminary tests showed that the prototype tube design, under normal operating conditions, is capable of achieving noise figures as low as 5 to 6 db. This tube, when operated under optimum beam-launching conditions and in a higher magnetic confining field, can have noise figures as low as 3 to 4 db. Cathode improvements are expected to reduce the noise figure of this basic design to approximately 2 to 3 db. Investigations showed that a reduction in the noise figure below the 2 to 3 db level requires a re design of the lownoise electron gun. The new electron gun desi conjunction with more efficient couplers and an improved focusing system, is expected to reduce the tube noise figure to the required 1 to 2 db level.