An electrostatically focused backward-wave oscillator

A new design of interdigital delay line has been developed for use with electrostatically focused backward-wave tubes. The shape of the delay line fingers has been modified by expanding their center portions into circular apertures. The delay line is divided into two electrically isolated parts so that successive fingers may be connected to different d.c. potentials, thus forming a series of electric lens elements. A hollow cylindrical electron beam which is projected along the delay line axis is electrostatically focused by the electron lens system.