Compact Switched-Beam Antennas Enabling Novel Power-Efficient Wireless Sensor Networks

Energy saving is one of the most important issues in wireless sensor network (WSN) context. The bottleneck of WSN nodes is the limited battery life and, in most cases, it is inconvenient or even impossible to replace the energetic module. Since the communication task is highly most power consuming, it is quite important to achieve an energy efficient communication in order to increase the lifetime of the devices through an intelligent use of the power transmission. In this paper, the integration of WSN nodes with switched-beam antennas is becoming more and more appealing due to the possibility to extend sensor node lifetime by optimizing the transmitted power. In this paper, a switched-beam antenna for WSNs nodes in the ISM band is proposed. The radiating structure consists of four identical antennas, composed of an array of two L-shaped quarter-wavelength slot antenna elements arranged in a compact and symmetrical planar structure. Thanks to a properly designed switching circuit which controls the feeding of the antenna elements, one among eight possible different radiation patterns in the azimuth plane (horizontal plane) can be selected on the basis of specific needs. Simulations and experimental results, referred to a prototype realized on an FR-4 substrate, demonstrate the appropriateness of the proposed switched-beam antenna system as hardware element enabling new power saving strategies in WSN contexts.