Enhanced harmonic generation in magnetrons

Abstract

An X-band rising sun harmonic-generator magnetron has been developed. In order to obtain enhanced second harmonic output power, the magnetron was designed so that the resonant frequency of the second-order π mode was twice the frequency of the first-order π mode. Second harmonic efficiency, the ratio of second harmonic output power to input power, was strongly magnetic field dependent. Large values of second harmonic efficiency and output power occurred for operation in the "valley of efficiency" of the rising sun anode, i.e., for magnetic fields near B=13,000/λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> gauss where λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> is the wavelength of the first-order π mode. Maximum second harmonic efficiency and output power at λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> =1.69 cm were 13 per cent and 46 kw, respectively. For operation at these magnetic fields the ratio of generated second harmonic to fundamental power was of the order unity. This large power ratio can be understood in terms of a phase shift between the fundamental voltage and the current which drives it, together with a modified rotating wave hypothesis where a waving motion, caused by the Γ=0 Hartree component of the azimuthal electric field, is superimposed on the conventional rotation of the space-charge spokes.