Use of multiple-helix circuits in 100-watt traveling-wave amplifiers

Abstract

Summary form only given. The problem of increasing the power level of a tw amplifier can be partially solved by using slow-wave circuits in parallel. It has been found that up to four helix circuits can be paralleled without adversely affecting the phase velocity characteristics, and that some increase in effective impedance may be realized. Paralleling is accomplished in a way which eliminates most of the unwanted propagation modes usually associated with coupled systems. 100-watt cw amplifiers for S and X band are described. These tubes use 4 helix slow-wave circuits, and are of metal ceramic construction. A 4-beam gun is used to provide a beam in each helix. In constructing the multiple-helix circuits, all helices are brazed together and are brazed in turn to sapphire rods to provide good cooling. Some loss in impedance is experienced due to dielectric loading. These tubes have saturation gains of the order of 20 per cent. The operating voltage is less than 3 kv, resulting in a relatively short tube. The X-band tube is short enough to permit permanent magnet focusing.