Vane-Loaded Planar Helix Slow-Wave Structure for Application in Broadband Traveling-Wave Tubes

Dispersion control of a planar helix slow-wave structure (SWS) using vane loading for applications in traveling-wave tubes has been studied. The addition of metal vanes and coplanar ground planes to the planar helix structure has been investigated with the help of simulations aimed at achieving low or negative dispersion. It is shown that, similar to the case of circular helix, the addition of metallic vanes to the planar helix can produce a flatter dispersion curve or negative dispersion characteristics. Furthermore, it is shown that even stronger dispersion control can be achieved by the use of metal vanes together with extended coplanar ground planes on the dielectric substrates that support the planar helix. As a proof of concept, one of the designs of the planar helix SWS including metal vanes and operating at S-band frequencies has been fabricated and tested; the measured phase velocity results match the simulation results very well.