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A low-cost, wideband, flexible antenna for radio frequency identification tags mountable on curved metal surfaces is presented. The antenna consists of a label-type patch adhering to a flexible polyvinyl chloride substrate. A novel balanced feed method using two orthogonal slits on the patch is proposed to perform simple and wideband impedance matching between the antenna and a tag chip. A prototype antenna was fabricated and tested with a commercial tag chip. It has a 3 dB return loss bandwidth of 70 MHz and a uniform read range of over 9.7 m in the 902 - 928 MHz range when it is mounted on a cylindrical metal plate with a radius of curvature of 150 mm.