This paper describes a novel large-displacement electrostatic “zipper” microactuator capable of achieving hundreds of microns of out-of-plane deflection, and application of fabricated microactuators to the control of millimeter-scale microfabricated capacitive pixels enabling “software-defined” microstrip antennas. The software-defined microstrip patch antenna concept relies on a reconfigurable array of individually addressed pixels. Current antenna designs demand pixel footprints below 1 mm2, with 300 μm vertical deflections, 1 ms response times, and low power consumption. To address this challenge we have developed a new technology based on electrostatic zipper actuation, in which a curved beam is switched between bistable states by application of a voltage across a dielectric film separating the beam from a flat electrode surface. This technology is novel in its use of SiO2 as both a high quality dielectric and the stressed layer of the bimorph providing curved actuation, enabling large out-of-plane deflection and large forces.