A wideband planar helix slow-wave structure for millimeter-wave TWTs

A wideband design of a slow-wave structure (SWS) consisting of planar helix with straight edge connections is proposed here. Dispersion is reduced by placing the metal shield close to the SWS, by including ground planes, and by reducing the amount of dielectric material. The design leads to an octave bandwidth centered at 30 GHz for the ‘cold’ SWS. The design can be implemented using microfabrication techniques. For a design with 150 periods and a 3750 V, 10 mA electron beam, a small-signal gain of 36 dB and a saturated output power of 6.65 W is predicted at 30 GHz. The design approach appears promising for wideband millimeter-wave traveling tubes.