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A low-cost, wideband planar antenna for RFID tags mountable on metallic surfaces has been presented in this paper. A novel proximity-coupled feed structure, in which the direction of the microstrip feedline is orthogonal to that of the resonant length of the radiating patch, has been explored to perform simple and wideband impedance matching between an antenna and a tag chip without any additional matching networks. The prototype of the antenna was fabricated and measured, and 57 MHz bandwidth at 3 dB return loss has been achieved
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Son et al. (2006) studied this question.