This paper presents the design, fabrication, and measurement of a novel, tunable, dual frequency rectangular slot antenna using RF MEMS technology. The antenna tuning is achieved by electrostatically actuated RF MEMS variable capacitors on a stub. Two different capacitor structures are implemented on the antenna: cantilever type and fixed-fixed beam type. The latter one is not sensitive to the stress on the structural layer and its measurement results agree well with the simulation results. Each antenna is fabricated monolithically using an in-house surface micromachining RF MEMS process on a 500-mu m thick glass substrate and occupies an area of about 21 mm x 18 mm. The measurement results show that the antenna resonant frequency can be tuned in a 1 GHz range in the X-band. (C) 2009 Elsevier B.V. All rights reserved.