ELECTRON BEAM TUBES

摘要

A linear electron beam tube comprises an electron gun (10) having a cathode and (12) a grid (13), and an anode (27) arranged in a first portion (24) of a drift tube (22). The drift tube is within a vacuum envelope (20) and has first and second portions (24, 26) separated by a gap (28) at which point an electron beam, density modulated with an input RF signal is inductively coupled to an output cavity (30). The vacuum envelope is partially defined by a cylindrical ceramic wall (18) and a pair of ferromagnetic pole pieces (14, 16) at its ends that form a DC magnetic circuit. The pole pieces extend radially beyond the vacuum envelope. At least those parts of the surface of the pole pieces that are in the RF path are coated with a layer of relatively low RF loss material such as copper. A balance ring separates the ceramic from the pole pieces. Further reduction in RF losses and relief from thermal stresses is obtained by forming the balance ring from the same ceramic as the cylindrical wall and metallising at least that part of the outer surface of the balance ring that forms part of an RF current path