High power, high efficiency TWT´S

Traditionally, traveling-wave tubes have been thought of as low-efficiency broadband devices. For single frequency operation and bandwidths up to 50mc, klystrons are adequate. Greater bandwidths are conventionally obtained using broadband traveling-wave tubes even though only a fraction of the tube´s actual bandwidth may be used. The development of a high efficiency traveling-wave tube that fills the gap between the klystron and the broadband traveling-wave tube, having bandwidths suitable for use in modern high resolution radar systems, is the subject of this paper. Several tubes utilizing the coupled cavity slow-wave circuit have been built and tested. These tubes have been designed to operate over a 200 mc band at X-band. The coupled cavity circuit offers the advantages of extreme ruggedness, good thermal properties, and integral pole pieces, which result in minimum magnet size and weight. As a result of narrow-banding, the gain per unit length is increased. This high gain per unit length of the circuit results in low phase sensitivity per unit gain. Phase sensitivity in the order of 5° for a 1% change in beam voltage has been measured on a 29db gain tube. Several high power narrow-band tubes have been constructed and tested. These tubes have power outputs of 100 to 200 kilowatts peak. Data will be presented on a tube with 29db of small signal gain. This tube has over 100kw peak power output, with the large signal gain flat within a total deviation of ±0.25 db over a bandwith of 160mc; the total weight of this tube is 10 pounds including focusing magnets. The efficiency is 33%, and with collector depression, the efficiency is over 40%. Tubes can be built with up to 60db small signal gain. A 45db gain tube has been constructed and tested, yielding similar results.