Abstract: Backward-wave oscillations in a helix or helix-derived traveling-wave tube re prevented by dimensioning the conductive shell surrounding the helix so that the backward-wave space harmonic of the slow-wave interaction circuit has a cutoff frequency in the vicinity of the frequency of the potential backward-wave oscillations. Lossy material is disposed between the shell and helix so that there is strong coupling between the electromagnetic field and the lossy material near the cutoff frequency of the backward-wave space harmonic.

Abstract: Ring-and-bar slow wave electronic interaction circuits of the singly and/or doubly connected variety are supported from a surrounding conductive barrel structure via the intermediary of ceramic comb structures which extend along the slow wave circuit. The ceramic "teeth" of the comb structure are brazed at their ends to the connecting bars of the slow wave circuit to enhance thermal conduction from the circuit. The free space between the teeth avoids excessive dielectric loading of the circuit. The "spines" of the ceramic combs are brazed to the barrel to provide good thermally conductive paths from the combs to the barrel for cooling of the slow wave circuit. A microwave tube employing a doubly connected ring-and-bar circuit, supported as aforedescribed, provides a high power structure having a small signal gain bandwidth between 3.7 db points of 6 GHz at Ku band.

Abstract: A frequency-selective stabilization system for a gyrotron traveling wave tube amplifier using a dielectrically loaded lossy auxiliary waveguide coupled to the interaction waveguide of the gyrotron traveling wave tube. The auxiliary waveguide has its cutoff frequency in the range of that of the interaction waveguide where instability is likely to occur, but has a significantly different dielectric constant, which lets it absorb stray oscillations in the range of the interaction waveguide cutoff frequency without significant interaction loss in the range of the operating frequency.