Stopbands produced by asymmetrical support rod system in helix structures

Following is a brief description of stopbands produced at the βρ = π phase point due to the asymmetry of the support system in the helix circuits. A stopband produced in this region of the ω-β diagram of the circuit results in reduction of the starting current for oscillation. There is also strong evidence that the "glitches" in the large-signal frequency response of wide-band high-power TWTs are caused by harmonic interaction at the high circuit impedance in the regions of the stopbands. Analysis of a simple model of the circuit show how the width of the stopband changes with angular displacement of one of the support rods, and with changes in the effective dielectric loading of one of the rods - the two most common forms of asymmetry. It will also be shown how the character of the stopbands is affected by distributed loss in the circuit.