Millimeter wave transmission line for slow phase velocity

A grounding plate and a transmission line are provided in a stack of dielectric material layers. First transmission line portions having a first width are alternately interlaced with second transmission line portions having a second width in the transmission line. The second width is greater than the first width so that inductance of the transmission line is increased relative to a transmission line having a fixed width. Metal fins may be provided between the grounding plate and the transmission line in the stack of the dielectric material layers. The metal fins may be grounded to the grounding plate to increase capacitance between the transmission line and the grounding plate. The increase in the inductance and the capacitance per unit length between the transmission line and the grounding plate is advantageously employed to provide a reduced phase velocity for electromagnetic signal transmitted through the transmission line. A design structure for the transmission line structure is provided.