An impedance matching device comprises a dielectric material having a ground plane affixed to one surface, a microstripline conductor disposed on an opposite surface, and a movable dielectric plate. The movable dielectric plate has a higher dielectric constant than the dielectric material, a user-selectable shape, and a conductive coating on the top surface. The bottom surface of the movable dielectric plate engages a portion of the microstripline conductor, and is movable transversely to the microstripline conductor to increase or decrease the impedance of the microstripline conductor and linearly to change the phase of the microstripline conductor.