Low-noise klystron amplifiers

Abstract

The principles of low-noise guns have been applied to klystron amplifiers with good corroboration of the theory. In the past, many people thought that klystrons had inherently high noise figures, while others advanced the theory that low-noise guns might be used with klystrons as well as with wave tubes. The development to be described here shows that the former impression is not true and verifies that low-noise klystron amplifiers are possible. The most obvious difference between the guns for low-noise klystron amplifiers and those typical of low-noise traveling-wave tubes is the higher beam current which is required for adequate klystron gain. A byproduct of this higher current is a wide dynamic range. In addition to the development of the electrical parameters, a major effort went into klystron construction techniques somewhat peculiar to low-noise klystron amplifiers. The data taken show that alignment of the low-noise gun electrodes with the drift tube, alignment of the beam with the magnetic field, elimination of the collector's secondary electrons from the beam, and cleanliness of the tube are of primary importance in constructing a low-noise klystron amplifier. Several two-cavity, low-noise klystron amplifiers were built for operation in both S-band and C-band. The typical low-level gain was 11.5 db, and the saturated power output was 180 mw. Several tubes exhibited noise figures below 9 db; the lowest value obtained was 6.7. db.