High frequency vacuum tube with closely spaced cathode and non-emissive

Abstract

A vacuum tube for handling an r.f. signal having a predetermined frequency range comprises a linear electron beam emitting cathode, a heater and a non-electron emissive current modulating grid. The grid is positioned from the cathode by the distance an emitted electron from the cathode can travel in a quarter cycle of the r.f. signal. Outer and inner coaxial metal tubes forming a resonant line of a signal coupler are respectively connected to the grid and cathode so electrons passing through the grid are in bundles in an interaction region between an accelerating anode and the grid. Ferrite tiles absorb r.f. fields in the interaction region. In one embodiment a signal coupling loop is between metal tubes at an end of the tubes spaced 3.lambda./4 from the grid and cathode. In a second embodiment the coupler includes a low voltage coaxial line having an inner conductor connected to a first metal face, spaced from a second opposed metal face by a solid dielectric. The coaxial outer conductor is connected to a third metal face, spaced from a fourth opposed metal face by the solid dielectric. The third and fourth faces surround the first and second faces. The first and third faces are at DC ground potential while the second and fourth faces are at high negative DC voltages. The second and fourth faces are respectively at common ends of interior and exterior coaxial metal tubes forming a .lambda./2 coupler. Other ends of the tubes are connected to the cathode and grid. Bias leads for the grid and cathode are connected to the exterior and interior tubes at positions .lambda./4 from the grid and cathode, while a heater lead goes through the interior tube at a position .lambda./4 from the grid and cathode.