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3-D antennas for narrow band, wireless sensor node applications are described herein. The antennas were designed on the surface of a cube which makes available the cube interior for sensor electronics placement. The layout of each antenna consists of a dipole fabricated on two sides of the cube and connected to a balanced-to-unbalanced line transition on the third side. The base of the cube serves as a ground plane for the microstrip feed line. The first cube antenna was designed for an operating frequency of 2.4 GHz and its 10 dB return loss bandwidth is 2%. Ka of the proposed design is 0.55 and its measured gain is 1.69 dBi with 78% measured radiation efficiency. The second cube antenna is similar to the first one but it was loaded with high dielectric constant superstrates. Ka of the second proposed antenna is 0.45, its measured gain is 1.25 dBi with 73% measured radiation efficiency and the bandwidth is 1.5%. The designs compare well with high efficiency, electrically small antennas that have been described in the open literature. A Wheeler Cap was used to measure the efficiency and the 3-antenna method was used for measuring the gain.
Date of Publication: Feb. 2012