A double octave low-noise traveling-wave amplifier with permanent-magnet focusing and integral power supply

A low-noise traveling-wave tube has been developed which operates over the two-octave band from 2 to 8 Gc. Typical rf characteristics are 10 dbm saturation power output with 8 db noise figure and 27 db small-signal gain. Gain variation of ± 2 db across the full band is achieved by the use of a severed helix with the output section operating at 450 volts, approximately twice the voltage of the input section. This allows the output helix voltage to be optimized for gain flatness and/or power output, while the input helix is set to the voltage for minimum noise figure. Beam current at the 10-milliwatt level is 500 µa. With the beam current reduced to 125 µa, noise figure of less than 6 db can be obtained over the full two octaves. Rf coupling to the helix is by means of a novel cavity transducer which permits input and output VSWR of less than 1.8. The complete amplifier, with integral power supply, is housed in a 4.5-inch diameter by 12-inch long package weighing 17 pounds, and is designed to comply with MIL-E-5400 environmental specifications.