The Satellite Traveling-Wave Tube

The output power amplifier in the Telstar spacecraft microwave repeater operates near 4 gc; the amplifier is required to accept a fractional milliwatt signal distributed over approximately 100 megacycles bandwidth and amplify it some 4000 times to provide an output of several watts. In the satellite, this power amplifier is the major power utilizing device, and its efficiency is controlling in the design of the satellite and of the system. Of the possible microwave devices which might be considered, the traveling-wave tube is outstandingly well suited to the application. The broad bandwidth and high gain is such that only a single tube is necessary. The efficiency is as high as or higher than that of competitive devices, and a considerable history exists to suggest that very long life and high reliability can be achieved. This paper describes the development of the M4041 traveling-wave tube for this application. The design methods for traveling-wave tubes for radio relay applications are well known and can be found in such texts as Ref. 1; therefore, discussion will be limited to those aspects which are peculiar to this application. Since reliability is the most important aspect in the Telstar experiment, considerable attention will be paid to this aspect of the design. The development of the tube was carried on in five phases. Initially, there was a design phase in which close interaction with the systems area produced a final amplifier specification 1703