A structure, using resonant coupling elements, suitable for a high-power travelling-wave tube

In the field of pulsed amplifiers for the megawatt output-power level, having high average power and 20% bandwidth at S-band frequencies, a promising structure seems to be a loop-coupled disc-loaded waveguide. The paper describes some of the properties of such structures. Of a number of possible pass-bands the two of principal interest are those of lowest frequency. If the loops are reversed, i.e. S-shaped, the lowest pass-band is a forward waveband and therefore useful for wide-band amplifier application, whilst the other is a backward-wave pass-band. In order to understand these pass-bands it is necessary to consider that the resonant waveguide sections are coupled together by other resonant elements¿the loops. A theory based on a simple model of this sort accords reasonably well with the observations. Structures having up to 48 loops have been measured and some characteristics are given. The conditions for maximum pass-band, concomitant with adequate Pierce impedance, have been studied. One potentially useful structure has 24 loops and a cold pass-band of 38% of the average frequency; about one-half of this should be available in amplifier operation.