Some proposals for generating high-frequency electromagnetic waves using the Doppler effect

It is shown theoretically that power may be transferred from a fundamental-frequency oscillation to a harmonic-frequency oscillation in a simple form of waveguide or resonator through the medium of a beam of bunched electrons. Important features are that the beam energy may be sub-relativistic and both its cross-section and that of the resonator are of dimensions comparable with the wavelength of the fundamental frequency. A possible application is shown to be a frequency multiplier for generating millimetre wavelengths for experimental purposes. At longer wavelengths efficient combined amplifiers and frequency multipliers appear feasible and capable of large power outputs because of the large beam cross-section compared with conventional beam devices. The relationship of the device to the undulator of Coleman and Motz and to a device of Kleinwÿchter´s is discussed, and it is shown that it may be regarded as an extension of these ideas.