Design and Performance of Coupled-helix Transducers for Travelling-wave Tubes†

This paper doseribos tho design and performance of couplod-helix transducers used to couple r.f. energy into and out of travelling-wave tubes; These transducers can be classified into (a) synchronous couplers in which tho phase velocities of tho signal on tho helices are the same, and (b) non-synchronous couplers in which the phase velocities of the waves on the coaxial helices differ. When used as input and output couplers for travelling-wave tubes, such dovices can be made to provide a good match over a broad frequency band. Principles underlying the operation of these transducers are discussed, together with the design procedure. Actual performance of those input and output couplers for use in travelling-wavo tubes operating in the S- and C-band. is included. Insertion loss, directivity, coupling length for optimum power transfer, and attainable bandwidth of such transducers are discussed briefly.