A phase shifter operable at microwave or millimeter-wave frequencies includes a dielectric substrate with a bottom surface having a conductive ground plane layer and a conductive patterned layer formed on a top surface to define a conductor pattern. A series of active tuning elements is mounted on the top surface and cascaded along a propagation direction in a spaced arrangement along a longitudinal extent. A housing structure includes a bottom housing structure with a planar conductive bottom surface for contacting the ground plane layer, and a top housing structure fabricated with a channel which extend along the longitudinal extent and provide clearance for the active tuning elements. A bias circuit is connected to the respective series of active tuning elements.