A Traveling-Wave Frequency Multiplier

A traveling-wave tube designed to operate as a frequency multiplier (twfm) is described, together with experimental results. The tube employs two helices in cascade, the output helix being a dispersive forward-wave helix operating at S band. A wide range of input frequencies can be used, and the dispersive character of the output helix permits the selection of a particular harmonic by voltage tuning of the helix. The experimental tube was designed to operate with an input frequency range of 0.5 to 1.0 kmc and an output range of 2 to 4 kmc, although it was found to have a useful input frequency range from 0.1 to 1.0 kmc. It was found that multiplication ratios up to 10 or 15 are feasible with substantial gain, and with output power corresponding to normal operation of the second helix as an amplifier. Using an input frequency as low as 0.1 kmc, well below the design value, harmonic output in the order of a few milliwatts has been obtained at harmonics as high as the fortieth. For beam powers of 2 to 4 watts and for input frequencies down to 0.25 kmc, the harmonic power varied from 20 to 100 mw, depending upon the output frequency and multiplication ratio. The gross features of the gain characteristics of the twfm using a cascade gain analysis are shown.