Millimetre-wave generator that uses a spiralling electron beam

A millimetre-wave generator that uses a helical electron beam spiralling around the axis of a nearly square wave-guide is described. The frequency of gyration round the axis is made equal to one-half of the signal frequency, thus halving the longitudinal magnetic field by comparison with those of cyclotron devices. Power outputs in excess of 2W at Q band wavelengths have been achieved with low-current, high-voltage beams, but the most important feature of the device is that the same electro-optical system can be used at considerably shorter wavelengths, for example λ = 2 mm. A brief historical introduction describes the development of this tube in relation to the better known cyclotron tubes.