The design and performance of a kilowatt traveling-wave amplifier for pulsed operation at 3000 mc/sec

A kilowatt traveling-wave amplifier is ordinarily operated in the large signal region where performance is influenced by many design considerations in addition to the small signal design parameters. Large signal analyses have not yet been able to accommodate the non-ideal attenuator and cannot consider the many extraneous effects observed in large signal operation. It is therefore necessary to modify the design as dictated by experimental results. A number of tubes of each design are ordinarily required to obtain conclusive results and insure against a "sport" or a "dud." Large signal performance is markedly affected by atteunator loss distribution and phase velocity under the attenuator. Observed performance sensitivity to helix velocity variation is not predicted by small signal theory. Low level backward-wave oscillations can markedly influence high level performance when harmonically related to the driving frequency. The design of the helix and attenuator support structure controls backward-wave oscillation and additionally influences other low level oscillations. The control of attenuator loss distribution, and the control of undesired output under no drive short circuited conditions appear to be basic problems in obtaining reproducible tube performance. Tubes made to the original design have been in operation in laboratory equipment since December, 1952. A redesign, recently made to ruggedize and to reduce size and magnet weight, has resulted in improved performance which is attributed to better control of attenuator characteristics and to the use of precision helices and helix supports.