Abstract: A magnetron has an output comprising a coaxial line 15 which transmits energy from a wanted oscillator mode as a first coaxial waveguide mode and energy from an unwanted oscillator mode as a second cylindrical waveguide mode. Energy in the cylindrical waveguide mode is intercepted by slots 17, 18 in the coaxial line 15 and absorbed by material 10. This enables the modes to be separated. Preferably, the output is taken from the axis of the magnetron and the wanted oscillator mode is the &pgr; mode.

Abstract: A grid for use in a linear electron beam tube such as an IOT or TWT includes a grid section and a focus electrode between which is included an accommodation portion. The grid is mounted in the tube by a mounting flange around its outer periphery. During use, the grid section becomes hot and consequently expands but the mounting flange remains relatively cool being connected to a relatively massive structure. Thin flexible strips of the accommodation section permit movement between the mounting flange and the grid section due to differential thermal expansion, thus minimising distortion to the grid section which might otherwise occur if it were connected directly to the mounting flange and hence fixed in its outer diameter length. In other embodiments, the focus electrode is omitted.

Abstract: A magnetron has an output comprising a coaxial line 15 which transmits energy from a wanted oscillator mode as a first coaxial waveguide mode and energy from an unwanted oscillator mode as a second cylindrical waveguide mode. Energy in the cylindrical waveguide mode is intercepted by slots 17, 18 in the coaxial line 15 and absorbed by material 19. This enables the modes to be separated. Preferably, the output is taken from the axis of the magnetron and the wanted oscillator mode in the &pgr;-1 mode.

Abstract: An r.f. radiation absorbing material able to hold off a 30 to 40 kV voltage difference is described as formed by a silicon rubber loaded with ferrite particles. The material is used to reduce self-oscillation in amplifiers.

Abstract: This invention relates to a co-axial magnetron in which a separate resonator incorporating a multipactor discharge arrangement is used to tune the operating frequency of the magnetron. The separate resonator is symmetrically coupled via couplers into the main resonator cavity of the magnetron. More than one separate resonant can be provided, in which case they are symmetrically coupled into the main resonant cavity to achieve correct tuning.