A square helix slow-wave structure for millimeter-wave TWTs

A square helix slow wave structure is proposed for high gain millimeter wave TWTs. The electromagnetic characteristics of this structure are calculated by HFSS. It is shown that, compared with the equivalent circular helix with the same cross section perimeter, the square helix structure holds higher interaction impedance and lower normalized phase velocity, which indicates higher output power and lower operating voltage in application of millimeter-wave TWT.