High power broadband coupled-cavity traveling-wave tubes

This paper describes the extension of the cold circuit bandwidth to 60 per cent and the operating bandwidth for high power traveling-wave tubes to 45 per cent. A new liquid cooled coupled-cavity circuit fulfills the bandwidth requirements and has high average power capability. In the process of increasing the bandwidth, a number of new problems required solution. The major difficulties encountered in wide-band operation are the spurious interaction at higher order modes, band edge oscillations, interaction impedance variation across the pass band and general operational instability because of regeneration. All of the above mentioned problems are magnified at higher operation voltages because of the merging of the fundamental and a particular higher order mode.