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The design, simulation, fabrication, measurement and performance of a V-band micro- strip delay line phase shifter using electrostatically actuated integrated micro-machined ground plane membranes are presented. The microstrip line is etched on an RFIC-friendly silicon substrate. The membrane is made of aluminium micro-ribbons and is fabricated on the ground plane side of the silicon substrate. The actuation of the ribbons away from the transmission line introduces an air gap between the radio-frequency (RF) substrate and the ground plane. By controlling the air gap thickness, a controllable phase shift in the transmission line is obtained. Each micro-ribbon measures 3.20 mm in length, 20 mum in width and 1 mum in thickness. A measured phase shift of 41deg at 50 GHz was achieved with an actuation voltage of 120 V. The fabrication process added a 20 mum initial air gap between the micro-ribbons and RF substrate, increasing the required actuation voltage for a given phase shift. The simulated phase shift results agree well with the measurements.