Development of a 13.5 db noise figure, 5-watt C-band traveling wave tube

A medium-power, PPM-focused, low-noise TWT has been developed for the 4 to 8 GHz bandwidth. Through special cathode shaping techniques and beam velocity profile in the gun region, a noise figure of 13.5 db maximum has been attained over the entire band. This achievement in itself is not particularly startling, but when coupled with the fact that the tube has a saturated power output of 5 watts minimum, the combination represents an elevation in the state of the art. The design employs a tungsten impregnated cathode operating at 2.1 amps/cm². The low noise figures have been obtained with both negative- and cathode-potential-grid guns employing beam divergence at the cathode surface. The helix design of the tube is loaded in a simple geometric fashion so as to give 3-1/2 db small signal gain flatness at the 45 db gain level over the octave. The tube is magnetically shielded and is fully environmentalized.