Device for attenuating very short parasitic waves in electronic tubes with coaxial, cylindrical electrodes

In a high frequency electronic tube having at least two coaxial cylindrical electrodes, a device for attenuating very short parasitic waves appearing at the ends of said coaxial electrodes, said parasitic waves generating between said electrodes high frequency electric fields normal to said electrodes, said electric fields being spatially periodic around the longitudinal axis of said electrodes and having changing sign around said axis, said attenuating device comprising a metal ring equipped with a plurality of elements capable of absorbing energy, said ring being disposed coaxially in relation to said two electrodes in a region of their ends thereof at which said parasitic waves develop, said ring being attached to the outermost of said two electrodes, and said plurality of elements capable of absorbing energy being constituted by elongated bands radially disposed around said conducting ring with the same spatial periodicity as that of the electric fields to be attenuated, said ring being furthermore disposed in such a way that said elements are placed at points around said electrodes where the sign of said parasitic electric fields is changing due to its spatial periodicity.