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01/14/1986
Patent Awarded for Linearized Traveling Wave Amplifier with Hard Limiter Characteristics
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Patent number: 4,564,787

LEW number: 13,981-2

Date issued: January 14, 1986

Assignee: NASA

Inventor: Henry G. Kosmahl

Abstract: The object of the invention is to provide a traveling wave tube with increased linearity to avoid intermodulation of signals being amplified. In a traveling wave tube 10, as shown in FIG. 1, the slow wave structure is a helix (18) including a sever (21). A dynamic velocity taper is provided by gradually reducing the spacing (26) between the repeating elements of the slow wave structure which are the windings of helix (18). The reduction takes place between Zo indicated by line 23 and Z.sub.s which coincides with the output point of helix (18) as indicated by the line (22). The spacing (26) begins to decrease at Z.sub.o and is decreased by up to about 5% at Z.sub.s. The spacing (26) between the repeating elements of the slow wave structure is ideally at an exponential rate because the curve (27), as shown in FIG. 3, increases from Z.sub.o to Zs the point of maximum efficiency and power, at an exponential rate. FIG. 3 shows a coupled cavity traveling wave tube having cavities 32 through 37. The axial length of cavities (35) through (37) is gradually reduced between Z.sub.o to Z.sub.s. To this end, the spacing between apertured discs 38 is gradually reduced between Z.sub.o and Z.sub.s from 0.1% to 5% at an exponential rate. In FIG. 4, curve 28 represents output power (or efficiency) versus input power for a commercial tube. Curve 31 represents the same parameters for a tube embodying the invention and shows the great linearity achieved by the dynamic velocity taper.

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