Low-profile Normal-Mode Helical Antenna for Use in Proximity to Metal
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Low-profile Normal-Mode Helical Antenna for Use in Proximity to MetalAbstract
To expand the applicability of UHF tags, a low-profile, small, normal-mode helical antenna (NMHA) that can be used on metallic plates was developed. This paper clarifies the design method for antenna structures for use in proximity to metal. The design data were obtained with the electromagnetic simulator FEKO. Fundamental electrical characteristics such as the antenna input impedances, self-resonance conditions, and radiation characteristics were clarified in proximity to metal. For antenna sizes of 0.03–0.05 wavelengths, antenna gains of about –0.5 dBd were achieved. The calculated results were verified using an actual antenna (size, 0.04 wavelengths). A tap feed structure was used for impedance matching. It was shown that very precise design results could be achieved. Moreover, the developed NMHA was designed to be a tag antenna. Here, the antenna impedance was matched to the IC chip impedance. The read range of the developed tag was measured to be about 15 m.
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References
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