A new micromachined wideband frequency reconfigurable microstrip patch antenna is demonstrated in this paper. The tunable antenna system is fabricated by a combination of surface and bulk micromachining processes. Thermal actuation is employed to precisely adjust the operating frequency with voltage ranges compatible with today's CMOS circuitries. A bulk micromachined silicon membrane containing thermal actuators serves as a platform for antenna patch. The patch is excited by a 50Ω feed line through proximity coupling. The out-of-plane motion of the thermal actuators normal to the antenna surface deflects the patch downward respect to the fixed ground plane. This deflection reduces the air gap height between the antenna patch and feed line and consequently, resonant frequency of the antenna. The effect of initial air gap height on achievable tuning range and bandwidth of the antenna is also investigated and the optimum range is presented. The up-state operating frequency of the antenna is 22.61GHz which continuously can be lowered to 22.17GHz. A tuning range of 440MHz was achieved by a CMOS compatible actuation voltage of 1.5V. The bandwidth of the antenna for up and down-state positions are 1.34 and 1.27GHz respectively. The RF performance of the antenna and its mechanical behavior is investigated by FEM analysis and satisfactory results are obtained within the tuning range.