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

A vacuum tube for handling an r.f. signal having a predetermined frequency range comprising a cathode for emitting an electron beam, a heater for the cathode positioned in close proximity to the cathode, a grid comprised of non-electron emissive material for current modulating the beam, the grid being positioned from the cathode no farther than a distance in which electrons emitted from the cathode can travel in a quarter cycle of the r.f. signal, an anode for accelerating the beam, an electrode for collecting the beam, an output cavity, resonant to a frequency of the r.f. signal, positioned between the grid and electrode for collecting the beam, a non-regenerative coupler for the r.f. signal connected to the grid and cathode so electrons from the cathode upon passing through the grid and accelerated toward the anode are in bundles in an interaction region between the anode and the closely spaced grid and cathode, the coupler including:

• inner and outer coaxial metal tubes which collectively comprise a resonant line having a length of at least .lambda./2, where .lambda. is the wavelength of the r.f. signal, the outer and inner tubes being electrically connected to the grid and cathode, respectively, the grid and outer coaxial tube being DC isolated from the cathode and inner coaxial tube, thereby enabling different DC voltages to be applied to the grid and cathode, first, second and third leads for respectively biasing the grid and cathode and for supplying current to the heater, the first and second leads being respectively connected to the outer and inner metal tubes at positions approximately n.sub.1 .lambda./4 from the grid and cathode and the third lead extending through the inner tube at a position approximately n.sub.1 .lambda./4 from the grid and cathode, where n.sub.1 is an odd integer.

A vacuum tube for handling an r.f. signal having a predetermined frequency range comprising a cathode for emitting a linear electron beam, a grid comprised of non-electron emissive material for current modulating the beam, the grid being positioned from the cathode no farther than a distance in which electrons emitted from the cathode can travel in a quarter cycle of the r.f. signal, an anode for accelerating the beam, an electrode for collecting the beam, an output cavity, resonant to a frequency of the r.f. signal, positioned between the grid and electrode for collecting the beam, a coupler responsive to the r.f. signal connected to the grid and cathode so electrons from the cathode upon passing through the grid and accelerated toward the anode are in bundles in an interaction region between the anode and grid to cause r.f. fields that are responsive to the signal to be derived in the interaction region, and r.f. absorbing material coupled to the interaction region for absorbing the r.f. fields so there is non-regenerative coupling of the r.f. signal to the region and there is heavy loading of the interaction region and formation of a resonant impedance in the interaction region is prevented, the heavy loading by the r.f. absorbing material of the interaction region and absorption of the r.f. fields tended to be generated by the bundled electrons in the interaction region being sufficiently great that there is no need to connect a capacitor or other high frequency low impedance component or circuit in shunt with the interaction region to by-pass the r.f. fields that tend to be generated by the bundled electrons.

A vacuum tube for handling an r.f. signal having a predetermined frequency range comprising a cathode for emitting a linear electron beam, a grid comprised of non-electron emissive material for current modulating the beam, the grid being positioned from the cathode no farther than a distance in which electrons emitted from the cathode can travel in a quarter cycle of the r.f. signal, an anode for accelerating the beam, an electrode for collecting the beam positioned downstream of the anode, an output cavity, resonant to a frequency of the r.f. signal, positioned between the grid and electrode for collecting the beam, a non-regenerative resonant coupler for the r.f. signal connected to the grid and cathode so electrons from the cathode upon passing through the grid and accelerated toward the anode are in bundles in an interaction region between the anode and the closely spaced grid and cathode, the coupler including:

• inner and outer coaxial metal tubes which collectively comprise a resonant line, the outer and inner metal tubes being respectively electrically connected to the grid and cathode, the grid and outer coaxial tube being DC isolated from the cathode and inner coaxial tube enabling different DC voltages to be applied to the grid and cathode, a loop disposed in a space between the outer and inner tubes at an end of the outer and inner tubes remote from the grid and cathode, the resonant coupler having a length of about n.lambda./4 between the grid and loop, where .lambda. is the wavelength of a frequency of the r.f. signal in the predetermined frequency range, and n is an odd integer.

A vacuum tube for handling an r.f. signal having a predetermined frequency range comprising a cathode for emitting an electron beam, a grid comprised of non-electron emissive material for current modulating the beam, the grid being positioned from the cathode no farther than a distance in which electrons emitted from the cathode can travel in a quarter cycle of the r.f. signal, an anode for accelerating the beam, an electrode for collecting the beam, an output cavity, resonant to a frequency of the r.f. signal, positioned between the grid and electrode for collecting the beam, a non-regenerative coupler for the r.f. signal connected to the grid and cathode so electrons from the cathode upon passing through the grid and accelerated toward the anode are in bundles in an interaction region between the anode and the closely spaced grid and cathode, the coupler including:

• a low voltage coaxial line having inner and outer conductors connected to a source of the r.f. signal, the inner conductor being connected to a first metal face, the first metal face being spaced from a second opposed metal face by a solid dielectric, the outer conductor being connected to a third metal face, the third face being spaced from a fourth opposed metal face by the solid dielectric, the third and fourth faces respectively being on structures surrounding the first and second faces, each of the metal faces having a respective periphery, the dielectric extending beyond the respective periphery of the metal faces so a substantial DC voltage can be established between the corresponding faces;
• the first and third faces being connected to a DC ground terminal, the second and fourth faces being connected to high negative DC voltage terminals, the second and fourth faces being respectively at common ends of inner and outer coaxial metal tubes thereby defining a half-wavelength coaxial coupler, the other ends of the inner and outer tubes being respectively connected to the cathode and grid.