A new concept in microwave gas switching elements

Abstract

A gas switching tube commonly known as a TR tube is an RF energy switch, the operation of which is a function of incident power level. Switch operation is achieved by gaseous ionization. The major problem in the design of gas switching devices has been that of achieving simultaneously a short recovery time and a low arc loss. This problem has been eliminated by the development of the device described in this paper. The design objective was to produce a self-contained TR window for operation at very high powers. The arc loss developed by conventional tube design at these high power levels would be sufficient to melt any known window material. The design of this device is such that the ionizable gas blanket takes the form of a thin-walled cylinder suspended in the iris in a dielectric cylinder. This configuration presents a smaller volume of gas with a reduced cross section and a much shorter diffusion length. These changes result in lower leakage power, faster recovery time, and reduced arc loss. As finally developed, the window does not involve glass-to-metal or ceramic-to-metal seals. The problem of metal sputtering or outgassing is therefore eliminated. By a unique spring pressure support, the problem of strain developed by differences of thermal coefficients of expansion is eliminated. The open-ended design of the cylinder provides excellent facilities for cooling the window. Prototype units have been successfully operated in "L" Band at power levels considerably in excess of 15 mw peak power and 30 kw average power. These units exhibited recovery times of 5 to 20 µsec with high-level attenuation of 26 to 35 db and arc loss below the level of present measuring techniques, i.e., < 0.02 db. A practical window for these high powers with a loaded Q of less than 1.5 has been fabricated.