An ultra-low noise PPM focused TWT

This paper describes a PPM focused ultra-low noise S-band TWT. Noise figures as low as 4.8 db have been attained. The noise figure was less than 5.2 db across 15% of S-band. The packaged amplifier weighs 3.5 lbs, and is completely magnetically shielded. The magnetic field over the cathode is 500 gauss. The uniform gun magnet is made of Alnico VIII and has mu metal flux straighteners. A cyclotron ripple canceling phenomenon utilizing the periodic nature of the transistion region is believed to provide best focusing and allow the anodes to be used to optomize the noise parameters. When the tube is operated in a PPM stack the noise figure is lower than when it is operated in a solenoid for fields up to 600 gauss. The saturated power output of this tube is 20 milliwatts; small signal gain, 30 db. The dynamic range is 15 db better than existing S-band ultra-low noise tubes. It is built to conform to MIL-E-5400 Class II specifications.