This paper reports a MEMS-based electrostatically tunable microstrip patch antenna fabricated using printed circuit processing techniques. The microstrip patch is patterned on the top side of the flexible kapton polyimide film, which is suspended above the fixed ground plane using a spacer. The air gap between the microstrip patch and the ground plane is decreased by applying a DC bias voltage between the patch and the ground plane. A decrease in air gap increases the effective permittivity of the antenna resulting in a downward shift in the resonant frequency. The microstrip patch is excited by a slot in the ground plane, which is inductively coupled by a coplanar waveguide (CPW) feed line. A 6 mm x 6 mm microstrip patch antenna tunable from 18.34 GHz at 0 V to 17.95 GHz at 268 V (with a tuning range of 390 MHz) is discussed.