Ultra wide band low-noise traveling-wave amplifiers

Recent work has resulted in the development of low-noise traveling-wave amplifiers capable of operating over frequency bands considerably in excess of one octave. One such amplifier covering the double-octave frequency band 2 to 8 GHz was reported at this conference last year. More recently, this work has been extended to cover a lower band greater than two octaves, namely, 0.5 to 2.1 GHz. At the present this amplifier has gained between 25 and 33 db, noise figure less than 6.5 db, and saturation power greater than 3 milliwatts. The unit unit incorporates an integral power supply and weighs less than 17 pounds. Coupling to the helix over this frequency range represents one of the principal technical problems. This is solved at the input by using a direct pin connection between the center conductor of the input coaxial line and the helix, with a typical VSWR of less than 2:1 resulting. The output match uses a coupled helix. In order to maintain flat gain the helix is severed, the input portion operating typically at 50 volts and output section at 75 volts. The parameter γa reaches a maximum value of 6.9 in the input helix.