Planar radiator with refined slot pattern for electrically small antennas

The authors present a novel radiator as a basic element of electrically small planar antennas for various short-range wireless applications. The proposed radiator takes advantage of its unique topology in order to improve a bandwidth of otherwise narrow-band conventional antennas. The radiator comprises a thin metal layer preferably formed on a surface of the dielectric substrate, and a slot pattern within that layer configured with four convoluted slot arms terminating a main slot at each end. One pair of terminating slot arms is convoluted clockwise while another pair is convoluted counterclockwise. The combination of clockwise and counterclockwise convoluted slot arms provides the termination with unique electromagnetic features. The slot arms are further formed as mirror-symmetrical couples with respect to the main slot line. The rigorous theoretical analysis is validated by precise prototyping and accurate experiments with UHF microstrip fed antennas. The bandwidth of the antenna with the proposed radiator becomes at least 30% wider without any affect on radiation pattern, gain, and polarisation purity. It is shown that improvement in the bandwidth has been achieved exclusively owing to the refined slot pattern.