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Directional and switched-beam antennas in wireless sensor networks are becoming increasingly appealing due to the possibility to reduce transmission power and consequently extend sensor node lifetime. In this work a reconfigurable beam-steering antenna is proposed for Wireless Sensor Network applications in the ISM band (f= 2.4-2.4835 GHz). The proposed radiating structure consists of a vertical half-wave dipole antenna and eight microstrip antennas composed of a rectangular two-element patch antenna array. These microstrip antennas have a directional radiation pattern in the azimuth plane with a HPBW of nearly 60 degrees. A control circuit consisting of a transmission line, RF-switches and a 4: 16 multiplexer has been designed in order to dynamically switch among nine radiation patterns, eight directional and one omnidirectional. Simulations and experimental results, referred to a low-cost realization on a FR4 substrate with a thickness of 1.6 mm, demonstrate appreciable performance.